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Azure SecurityNotesLessons Learned from

Exploring Microsoft Azure and the Cloud Security Space

J.D. Meier, Principal PM, MicrosoftPaul Enfield


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Acknowledgments

Thanks to the following external contributors and reviewers:

Adam Grocholski; Andy Eunson; Bill Collette; Christopher Seary; Jason Taylor; John Daniels;

Juval Lowy; Kevin Lam; Long Le; Michael Smith; Michael Stiefel; Michele Leroux Bustamante;

Norman Headlam; Rockford Lhotka; Rudolph Araujo; Sarang Kulkarni; Steven Nagy; Terrance

Snyder; Will Clevenger

Thanks to the following Microsoft contributors and reviewers:

Akshay Aggarwal; Alik Levin; Andreas Fuchsberger; Babur Butter; Bharat Shyam; Dave Brankin;

Danny Cohen; Diego Dagum; Don Willits; Eugenio Pace; Gabriel Morgan; Jeff Mueller; John

Steer; Julian Gonzalez; Mark Curphey; Mohit Srivastava; Pat Filoteo; Rahul Verma; Raul Rojas;

Scott Densmore; Sesha Mani; Serena Yeoh; Sriram Krishnan; Stefan Schackow; Steve Marx;

Stuart Kwan; Terri Schmidt; Tobin Titus; Varun Sharma; Vidya Vrat Agarwal; Vikram Bhambri;

Yale Li


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Our Cloud Security Approach

Objectives Learn a security frame Learn an approach for applying the security frame to application scenarios Learn key components of the security approach for these notes

OverviewThese notes summarize how we took a look at securing Web applications, web services, and

data in the cloud. We basically started by mapping out common application scenarios. We

then figured out a way to group threats and attacks into a set of common categories. These

categories make it easy for us to analyze and inspect the various parts of an application andengineering decisions. Then we focused on finding common principles, patterns, and practices,

while working with customers, field, product teams, and industry experts.

Our Cloud Security Approach in a NutshellWe took a pragmatic approach to security, identifying key deltas, building on what we know,

and leveraging proven practices. Here are some of the cornerstone concepts we used to focus

and drive our security efforts:

Visual Application Scenarios and Solutions. We created simple visuals that show end-to-end scenarios. You can think of these as how you might put on a whiteboard if you were to

draw the end in mind for a particular application scenario. This is a simple way to share

authentication and authorization patterns for common application scenarios.

Secure the network, host, and application. Ask any security expert, where the problemsare, and theyll say its the stuff that falls between the cracks. Thinking about security

holistically across the network, host, and application is the key to both helping you focus

your efforts, as well as catching what falls between the cracks.

Principles, patterns, and practices. Design principles help you leverage proven practices.Rather than have a rule for everything, you have a smaller set of principles to guide you.

Patterns are simply problem and solution pairs in context. They help share strategies and

principles by building a shared vocabulary. For example, the Trusted Subsystem pattern

http://msdn.microsoft.com/en-us/library/ff649178.aspxencapsulates the idea of trusting

the application identity rather than every caller. Practices are simply actions, methods, ortechniques. For example, you can use patterns & practices Threat Modeling

http://msdn.microsoft.com/en-us/library/ff648006.aspxto shape the security design of

your application.

Threats and countermeasures. One way to make security actionable and prescriptive is tofocus on threats and countermeasures. This means identifying the bad things that can

happen, and what your defenses, security controls, or countermeasures are.
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Security Frame. There are many ways to chunk up and think about security. For example,you might use C.I.A., where C is confidentiality, I is integrity, and A represent availability.

Another approach is to focus on the three As: Authentication, Access control, and Auditing.

Weve found it especially useful to use the following categories to organize and share

application security principles, patterns, anti-patterns, and practices: Auditing and

Logging, Authentication, Authorization, Communication, ConfigurationManagement, Cryptography, Exception Management, Sensitive Data, Session

Management, and Validation.

People, process, and technology. Another way to look at security is through the people,process, and technology viewpoints. You can also use each of these views when you look

at security for your network, host, and application.

Application, Infrastructure, and Business. This is another helpful lens for looking atsecurity. You can look at the principles, patterns, and practices for the application, the

infrastructure, or the business. This leads to application security patterns, infrastructure

security patterns, and business security patterns and practices.

At the end of the day, whats important is using the lens that helps you the most, and avoid

using the wrong tool for the job, or using a one-size fits all solution. Instead, chunk up the

problem, while keeping a holistic view.

How We Got StartedTackling cloud security can be overwhelming without an approach. In these notes, we have an

approach that simplifies and improves security. It does so by chunking up security in a way that

helps us leverage proven practices, while sharing information around emerging practices.

One way to simplify thinking about security is to simplify the language. When we first started

talking with customers about the cloud and security, it was difficult to have meaningful

conversations, simply because we didnt have a shared vocabulary.

Using a threats and countermeasures approach to talk about security is a key step to simplifying

cloud security. Basically, we can look through our security lens (our security frame), and look

for threats, attacks, vulnerabilities, and countermeasures. We can use that same lens and look

for principles, patterns, and anti-patterns. This helps us turn security information into insight

and action.

Another important step is leveraging application types from the patterns & practices

Application Architecture Guide, second edition -http://msdn.microsoft.com/en-us/library/ff650706.aspx. Rather than focus on queues and worker roles, we can shift our

focus to application scenarios, and represent them visually. Our goal is to show how to secure

your Web application, Web services, and data in the cloud visually. With these scenarios we

can move to the whiteboard and draw end-to-end scenarios.
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By using a security frame, focusing on threats and countermeasures, and visual scenarios, we

have an effective backdrop for analyzing, evaluating, and talking about cloud security

challenges.

Threats and Countermeasures FocusOne way to make security actionable and prescriptive is to focus on threats, attacks,

vulnerabilities and countermeasures:

Threat - A potential occurrence malicious or otherwise that may harm an asset. Attack - An action taken to harm an asset. Vulnerability - A weakness that makes a threat possible. Countermeasure - A safeguard that addresses a threat and mitigates risk.This means identifying the bad things that can happen, and what your defenses, security

controls, or countermeasures are. By building a knowledgebase of threats, attacks,

vulnerabilities, and countermeasures, we can dramatically improve our ability to share securityknow-how.

Example Application Scenario and SolutionEach Visual Scenario and Solution consists of a Scenario, Solution, and Solution Summary Table.

The Scenario is a simple visual of the application from a deployment standpoint. The Solution is

a visual of how you might address authentication, authorization, and communication (the

security runtime patterns.) The Solution Summary Table is a quick description of how you

would address the authentication, authorization, and communication from a security

standpoint.

Scenario


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Solution

Solution Summary Table

Area Notes

Authentication Authenticate users with forms authentication Store users in Azure Tables Use TableStorageMembershipProvider for membership APIs Authenticate application against Azure Storage with access key Map ASP.NET users to single Azure Storage connection All access to the database occurs as the application identity

Authorization Use TableStorageRoleProvider for roles APIs Authorize users in application logic Store roles in Azure Tables

Communication Use HTTP port 80 for non-secure connections to ASP.NET application Perform forms authentication over port 443 (SSL)

Security FrameA Security Frame acts as a simple lens. It helps organize and share security knowledge in a set

of actionable buckets. Here is an explanation of the key buckets used in these notes:

Category Notes

Auditing and Logging How security-related events are recorded, monitored, and audited.

Authentication The process of proving identity, typically through credentials, such as a user

name and password

Authorization How your application provides access controls for roles, resources and

operations.

Communication How data is transmitted over the wire. Transport security versus message

encryption is covered here.

Configuration

Management

How your application handles configuration and administration of your

applications from a security perspective.

Cryptography How your application enforces confidentiality and integrity.

Exception

Management

How you handle applications errors and exceptions.

Sensitive Data How your application handles any data that must be protected either in


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memory, over the network, or in persistent stores

Session Management A session refers to a series of related interactions between a user and your

application.

Validation How your application filters, scrubs, or rejects input before additional

processing, or how it sanitizes output.

The key to the buckets is that they are actionable. Another key is that developers can relate to

them. This makes it easier to share security knowledge between security experts and

developers in a pragmatic way.

Carrying the Story ForwardImproving Web Application Security: Threats and Countermeasures

(http://msdn.microsoft.com/en-us/library/ff649874.aspx) illustrates the approach of securing a

solution by addressing key security hotspots defined by the security frame in Figure 1 below.

This visual model allows you to conceptualize specific areas and items in an architecture that

need to be addressed during the process of securing an application. The visual model

represents a fairly typical on-premise application architecture, and then pins hotspots against

it.

Figure 1. Securing the Network, Host and Application On-premise

Using this visual model concept and the revised security frame for cloud applications we can

use the same approach to evaluate cloud applications. In Figure 2 below, we modify the visual

Database

Web

Server

Application

Server

Database

Server

Firewall Apps

Firewall Apps

Host Host

Patches and UpdatesServicesProtocols

AccountsFiles and DirectoriesShares

Securing the Host

Host

RouterFirewallSwitch

Securing the

Network PortsRegistryAuditing and Logging

Threats and Countermeasures

Exception ManagementParameter ManipulationSensitive DataSession ManagementValidation

Auditing and LoggingAuthenticationAuthorizationConfiguration Mgt.Cryptography

Securing the Application
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model by hosting both the application and data layers in the managed infrastructure, which in

this case is the cloud. With a managed infrastructure we can remove checks from our list

because they are items handled by the managed infrastructure. For example, a Windows Azure

application will not have permissions to create user accounts, or elevate privileges. This

alleviates the need to manage accounts at the host level.

Firew

all Apps

Cloud Host

Threats and Countermeasures

Data

ApplicationLayer

Managed

Infrastructure

DatabaseLayer

Patches and UpdatesServicesProtocols

AccountsFiles and DirectoriesShares

PortsRegistryAuditing and Logging

Securing the Host

CryptographyException ManagementSensitive DataSession ManagementValidation

Auditing and LoggingAuthenticationAuthorizationCommunication

Configuration Management

Securing the Application

RouterFirewallSwitch

Securing the

Network

Figure 2. Securing the Network, Host and Application in the Cloud

The above diagram represents the canonical case architecture. To evaluate other architectures

such as ones involving federated identity or hybrid on-premise and cloud implementations, you

can use the same approach. Represent your architecture with a base diagram, and overlay the

frame on it. Once the frame is overlaid, you can evaluate each item for applicability and quickly

scope out categories not needing attention.


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Cloud Security Threats and Countermeasures

Objectives Learn a security frame that applies to the cloud. Learn top threats/attacks, vulnerabilities and countermeasures for each area within the

security frame.

Understand differences between threats, attacks, vulnerabilities and countermeasures.

OverviewIt is important to think like an attacker when designing and implementing an application.

Putting yourself in the attackers mindset will make you more effective at designing mitigations

for vulnerabilities and coding defensively. This section is a reference of the security frame, andits pieces pinned against the cloud as a platform. We also present threats, vulnerabilities and

countermeasures against the cloud organized by hot spot such that you can see how they relate

to each other in each category.

Threats, Attacks, Vulnerabilities, and CountermeasuresThis chapter analyzes security from the perspectives of threats, vulnerabilities, attacks, and

countermeasures against the cloud. These terms are defined as follows:

Asset. A resource of value such as the data in a database, data on the file system, or asystem resource.

Threat. A potential occurrence malicious or otherwise that can harm an asset. Vulnerability. A weakness that makes a threat possible. Attack. An action taken to exploit vulnerability and realize a threat. Countermeasure. A safeguard that addresses a threat and mitigates risk.Cloud Security FrameThe following key security concepts provide a frame for thinking about security when designing

and architecting Windows Azure applications. Understanding these concepts helps you put core

security features such as authentication, authorization, auditing, confidentiality, integrity, and

availability in action.

Hot Spot Description

Auditing and

Logging

Auditing and logging in Windows Azure refers to how security-related events

are recorded, monitored, audited, exposed, compiled & partitioned across

multiple cloud instances. Examples include: Who did what and when and on

which VM instance?

Authentication Authentication is the process of proving identity, typically through credentials,

such as a user name and password. In the cloud this also encompasses


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authentication against varying identity stores.

Authorization Authorization in Windows Azure is how your application provides access

controls for roles, resources and operations. Authorization strategies might

involve standard mechanisms, utilize claims and potentially support a federated

model.

Communication Communication encompasses how data is transmitted over the wire. Transportsecurity, message encryption, and point to point communication are covered

here.

Configuration

Management

Configuration management refers to how your application handles

configuration and administration of your applications from a security

perspective. Examples include: Who does your application run as? Which

databases does it connect to? How is your application administered? How are

these settings secured?

Cryptography Cryptography in Windows Azure refers to how your application enforces

confidentiality and integrity. Examples include: How are you keeping secrets

(confidentiality)? How are you tamper-proofing your data or libraries

(integrity)? How are you providing seeds for random values that must be

cryptographically strong? Certificates and cert management are in this domain

as well.

Input and Data

Validation

Validation refers to how your application filters, scrubs, or rejects input before

additional processing, or how it sanitizes output. It's about constraining input

through entry points and encoding output through exit points. Message

validation refers to how you verify the message payload against schema, as well

as message size, content and character sets. Examples include: How do you

know that the input your application receives is valid and safe? Do you trust

data from sources such as databases and file shares?

Exception

Management

Exception management refers to how you handle applications errors and

exceptions. Examples include: When your application fails, what does your

application do? Does it support graceful failover to other application instancesin the cloud? How much information do you reveal? Do you return friendly

error information to end users? Do you pass valuable exception information

back to the caller?

Sensitive Data Sensitive data refers to how your application handles any data that must be

protected either in memory, over the network, or in persistent stores. Examples

include: How does your application handle sensitive data? How is sensitive data

shared between application instances?

Threats and Attacks

Category Items

Auditing and

Logging

Disclosure of confidential information. An attacker gathers sensitiveinformation from log files.

Denial of service (DoS). An attacker overwhelms logs with excessive entriesor very large log entries.


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Repudiation. An attacker denies performing an operation, exploits anapplication without trace, or covers his or her tracks.

Authentication Network eavesdropping. An attacker steals identity and/or credentials offthe network by reading network traffic not intended for them.

Brute force attacks. An attacker guesses identity and/or credentials throughthe use of brute force.

Dictionary attacks. An attacker guesses identity and/or credentials throughthe use of common terms in a dictionary designed for that purpose.

Cookie replay attacks. An attacker gains access to an authenticated sessionthrough the reuse of a stolen cookie containing session information.

Credential theft. An attacker gains access to credentials through data theft;for instance, phishing or social engineering.

Authorization Elevation of privilege. An attacker enters a system as a lower-level user, butis able to obtain higher-level access.

Disclosure of confidential data. An attacker accesses confidentialinformation because of authorization failure on a resource or operation.

Data tampering. An attacker modifies sensitive data because ofauthorization failure on a resource or operation.

Luring attacks. An attacker lures a higher-privileged user into taking anaction on their behalf. This is not an authorization failure but rather a failure

of the system to properly inform the user.

Token stealing. An attacker steals the credentials or token of another user inorder to gain authorization to resources or operations they would not

otherwise be able to access.

Communication Failure to encrypt messages. An attacker is able to read message content offthe network because it is not encrypted.

Theft of encryption keys. An attacker is able to decrypt sensitive databecause he or she has the keys.

Man-in-the-middle attack. An attacker can read and then modify messagesbetween the client and the service.

Session replay. An attacker steals messages off the network and replaysthem in order to steal a user's session.

Data tampering. An attacker modifies the data in a message in order toattack the client or the service

Configuration

Management

Unauthorized access to configuration stores. An attacker gains access toconfiguration files and is able to modify binding settings, etc.

Retrieval of clear text configuration secrets. An attacker gains access toconfiguration files and is able to retrieve sensitive information such as

database connection strings.

Cryptography Encryption cracking. Breaking an encryption algorithm and gaining access tothe encrypted data.

Loss of decryption keys. Obtaining decryption keys and using them to accessprotected data.

Exception

Management

Information disclosure. Sensitive system or application details are revealedthrough exception information.

Denial of service. An attacker uses error conditions to stop your service orplace it in an unrecoverable error state.


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Elevation of privilege. Your service encounters an error and fails to aninsecure state; for instance, failing to revert impersonation.

Input and Data

Validation

Canonicalization attacks. Canonicalization attacks can occur anytimevalidation is performed on a different form of the input than that which is

used for later processing. For instance, a validation check may be performed

on an encoded string, which is later decoded and used as a file path or URL. Cross-site scripting. Cross-site scripting can occur if you fail to encode user

input before echoing back to a client that will render it as HTML.

SQL injection. Failure to validate input can result in SQL injection if the inputis used to construct a SQL statement, or if it will modify the construction of a

SQL statement in some way.

Cross-Site Request Forgery: CSRF attacks involve forged transactionssubmitted to a site on behalf of another party.

XPath injection. XPath injection can result if the input sent to the Webservice is used to influence or construct an XPath statement. The input can

also introduce unintended results if the XPath statement is used by the Web

service as part of some larger operation, such as applying an XQuery or an

XSLT transformation to an XML document.

XML bomb. XML bomb attacks occur when specific, small XML messages areparsed by a service resulting in data that feeds on itself and grows

exponentially. An attacker sends an XML bomb with the intent of

overwhelming a Web services XML parser and resulting in a denial of service

attack.

Sensitive Data Memory dumping. An attacker is able to read sensitive data out of memoryor from local files.

Network eavesdropping. An attacker sniffs unencrypted sensitive data offthe network.

Configuration file sniffing. An attacker steals sensitive information, such asconnection strings, out of configuration files.

Vulnerabilities

Category Items

Auditing and

Logging

Failing to audit failed logons. Failing to secure log files. Storing sensitive information in log files. Failing to audit across application tiers. Failure to throttle log files.

Authentication Using weak passwords. Storing clear text credentials in configuration files. Passing clear text credentials over the network. Permitting prolonged session lifetime. Mixing personalization with authentication. Using weak authentication mechanisms (e.g., using basic authentication over


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an untrusted network).

Authorization Relying on a single gatekeeper (e.g., relying on client-side validation only). Failing to lock down system resources against application identities. Failing to limit database access to specified stored procedures. Using inadequate separation of privileges. Connection pooling. Permitting overprivileged accounts.

Configuration

Management

Using insecure custom administration interfaces. Failing to secure configuration files on the server. Storing sensitive information in the clear text. Having too many administrators. Using overprivileged process accounts and service accounts.

Communication Not encrypting messages. Using custom cryptography. Distributing keys insecurely. Managing or storing keys insecurely. Failure to use a mechanism to detect message replays. Not using either message or transport security.

Cryptography Using custom cryptography Failing to secure encryption keys Using the wrong algorithm or a key size that is too small Using the same key for a prolonged period of time Distributing keys in an insecure manner

Exception

Management

Failure to use structured exception handling (try/catch). Revealing too much information to the client. Failure to specify fault contracts with the client. Failure to use a global exception handler.

Input and DataValidation

Using non-validated input used to generate SQL queries. Relying only on client-side validation. Using input file names, URLs, or usernames for security decisions. Using application-only filters for malicious input. Looking for known bad patterns of input. Trusting data read from databases, file shares, and other network resources. Failing to validate input from all sources including cookies, headers,

parameters, databases, and network resources.

Sensitive Data Storing secrets when you do not need to. Storing secrets in code. Storing secrets in clear text in files, registry, or configuration. Passing sensitive data in clear text over networks.

Countermeasures

Category Items


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Auditing and

Logging

Identify malicious behavior. Know your baseline (know what good traffic looks like). Use application instrumentation to expose behavior that can be monitored. Throttle logging. Strip sensitive data before logging.

Authentication Use strong password policies. Do not store credentials in an insecure manner. Use authentication mechanisms that do not require clear text credentials to

be passed over the network.

Encrypt communication channels to secure authentication tokens. Use Secure HTTP (HTTPS) only with forms authentication cookies. Separate anonymous from authenticated pages. Using cryptographic random number generators to generate session IDs.

Authorization Use least-privileged accounts. Tie authentication to authorization on the same tier. Consider granularity of access. Enforce separation of privileges. Use multiple gatekeepers. Secure system resources against system identities.

Configuration

Management

Using insecure custom administration interfaces. Failing to secure configuration files on the server. Storing sensitive information in the clear text. Having too many administrators. Using overprivileged process accounts and service accounts.

Communication Use message security or transport security to encrypt your messages. Use proven platform-provided cryptography. Periodically change your keys. Use any platform-provided replay detection features. Consider creating custom code if the platform does not provide a detection

mechanism.

Turn on message or transport security.Cryptography Do not develop and use proprietary algorithms (XOR is not encryption. Use

established cryptography such as RSA)

Avoid key management. Use the RNGCryptoServiceProvider method to generate random numbers Periodically change your keys

Exception

Management

Use structured exception handling (by using try/catch blocks). Catch and wrap exceptions only if the operation adds value/information. Do not reveal sensitive system or application information. Implement a global exception handler. Do not log private data such as passwords.

Sensitive Data Do not store secrets in software. Encrypt sensitive data over the network. Secure the channel. Encrypt sensitive data in configuration files.

Validation Do not trust client input.


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Validate input: length, range, format, and type. Validate XML streams. Constrain, reject, and sanitize input. Encode output. Restrict the size, length, and depth of parsed XML messages.

Threats and Attacks Explained

1. Brute force attacks. Attacks that use the raw computer processing power to try differentpermutations of any variable that could expose a security hole. For example, if an attacker

knew that access required an 8-character username and a 10-character password, the

attacker could iterate through every possible (256 multiplied by itself 18 times) combination

in order to attempt to gain access to a system. No intelligence is used to filter or shape for

likely combinations.2. Buffer overflows. The maximum size of a given variable (string or otherwise) is exceeded,

forcing unintended program processing. In this case, the attacker uses this behavior to

cause insertion and execution of code in such a way that the attacker gains control of the

program in which the buffer overflow occurs. Depending on the programs privileges, the

seriousness of the security breach will vary.

3. Canonicalization attacks. There are multiple ways to access the same object and anattacker uses a method to bypass any security measures instituted on the primary intended

methods of access. Often, the unintended methods of access can be less secure deprecated

methods kept for backward compatibility.

4. Cookie manipulation. Through various methods, an attacker will alter the cookies stored inthe browser. Attackers will then use the cookie to fraudulently authenticate themselves to a

service or Web site.

5. Cookie replay attacks. Reusing a previously valid cookie to deceive the server into believingthat a previously authenticated session is still in progress and valid.

6. Credential theft. Stealing the verification part of an authentication pair (identity +credentials = authentication). Passwords are a common credential.

7. Cross-Site Request Forgery (CSRF). Interacting with a web site on behalf of another user toperform malicious actions. A site that assumes all requests it receives are intentional is

vulnerable to a forged request.

8. Cross-site scripting (XSS). An attacker is able to inject executable code (script) into a streamof data that will be rendered in a browser. The code will be executed in the context of theusers current session and will gain privileges to the site and information that it would not

otherwise have.

9. Connection pooling. The practice of creating and then reusing a connection resource as aperformance optimization. In a security context, this can result in either the client or server

using a connection previously used by a highly privileged user being used for a lower-

privileged user or purpose. This can potentially expose vulnerability if the connection is not

reauthorized when used by a new identity.


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10.Data tampering. An attacker violates the integrity of data by modifying it in local memory,in a data-store, or on the network. Modification of this data could provide the attacker with

access to a service through a number of the different methods listed in this document.

11.Denial of service. Denial of service (DoS) is the process of making a system or applicationunavailable. For example, a DoS attack might be accomplished by bombarding a server with

requests to consume all available system resources, or by passing the server malformedinput data that can crash an application process.

12.Dictionary attack. Use of a list of likely access methods (usernames, passwords, codingmethods) to try and gain access to a system. This approach is more focused and intelligent

than the brute force attack method, so as to increase the likelihood of success in a shorter

amount of time.

13.Disclosure of sensitive/confidential data. Sensitive data is exposed in some unintendedway to users who do not have the proper privileges to see it. This can often be done

through parameterized error messages, where an attacker will force an error and the

program will pass sensitive information up through the layers of the program without

filtering it. This can be personally identifiable information (i.e., personal data) or system

data.

14.Elevation of privilege. A user with limited privileges assumes the identity of a privilegeduser to gain privileged access to an application. For example, an attacker with limited

privileges might elevate his or her privilege level to compromise and take control of a highly

privileged and trusted process or account. More information about this attack in the

context of Windows Azure can be found in the Security Best Practices for Developing

Windows Azure Applications at

http://www.microsoft.com/downloads/details.aspx?displaylang=en&FamilyID=0ff0c25f-

dc54-4f56-aae7-481e67504df6

15.Encryption. The process of taking sensitive data and changing it in such a way that it isunrecognizable to anyone but those who know how to decode it. Different encryptionmethods have different strengths based on how easy it is for an attacker to obtain the

original information through whatever methods are available.

16.Information disclosure. Unwanted exposure of private data. For example, a user views thecontents of a table or file that he or she is not authorized to open, or monitors data passed

in plaintext over a network. Some examples of information disclosure vulnerabilities include

the use of hidden form fields, comments embedded in Web pages that contain database

connection strings and connection details, and weak exception handling that can lead to

internal system-level details being revealed to the client. Any of this information can be very

useful to the attacker.

17.Luring attacks. An attacker lures a higher-privileged user into taking an action on his or herbehalf. This is not an authorization failure but rather a failure of the system to properly

inform the user.

18.Man-in-the-middle attacks. A person intercepts both the client and server communicationsand then acts as an intermediary between the two without each ever knowing. This gives

the middle man the ability to read and potentially modify messages from either party in

order to implement another type of attack listed here.
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19.Network eavesdropping. Listening to network packets and reassembling the messagesbeing sent back and forth between one or more parties on the network. While not an attack

itself, network eavesdropping can easily intercept information for use in specific attacks

listed in this document.

20.Open Redirects. Attacker provides a URL to a malicious site when allowed to input a URLused in a redirect. This allows the attacker to direct users to sites that perform phishingattacks or other malicious actions.

21.Password cracking. If the attacker cannot establish an anonymous connection with theserver, he or she will try to establish an authenticated connection. For this, the attacker

must know a valid username and password combination. If you use default account names,

you are giving the attacker a head start. Then the attacker only has to crack the accounts

password. The use of blank or weak passwords makes the attackers job even easier.

22.Repudiation. The ability of users (legitimate or otherwise) to deny that they performedspecific actions or transactions. Without adequate auditing, repudiation attacks are difficult

to prove.

23.Session hijacking. Also known as man-in-the-middle attacks, session hijacking deceives aserver or a client into accepting the upstream host as the actual legitimate host. Instead,

the upstream host is an attackers host that is manipulating the network so the attackers

host appears to be the desired destination.

24.Session replay. An attacker steals messages off of the network and replays them in order tosteal a users session.

25.Session fixation. An attacker sets (fixates) another persons session identifier artificially. Theattacker must know that a particular Web service accepts any session ID that is set

externally; for example, the attacker sets up a URL such as

http://unsecurewebservice.com/?sessionID=1234567. The attacker then sends this URL to a

valid user, who clicks on it. At this point, a valid session with the ID 1234567 is created on

the server. Because the attacker determines this ID, he or she can now hijack the session,which has been authenticated using the valid users credentials.

26.Spoofing. An attempt to gain access to a system by using a false identity. This can beaccomplished by using stolen user credentials or a false IP address. After the attacker

successfully gains access as a legitimate user or host, elevation of privileges or abuse using

authorization can begin.

27.SQL injection. Failure to validate input in cases where the input is used to construct a SQLstatement or will modify the construction of a SQL statement in some way. If the attacker

can influence the creation of a SQL statement, he or she can gain access to the database

with privileges otherwise unavailable and use this in order to steal or modify information or

destroy data.28.Throttling. The process of limiting resource usage to keep a particular process from bogging

down and/or crashing a system. Relevant as a countermeasure in DoS attacks, where an

attacker attempts to crash the system by overloading it with input.


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Countermeasures Explained

1. Assume all input is malicious. Assuming all input is malicious means designing yourapplication to validate all input. User input should never be accepted without being filtered

and/or sanitized.

2. Audit and log activity through all of the application tiers. Log business critical and securitysensitive events. This will help you track security issues down and make sense of security

problems. Skilled attackers attempt to cover their tracks, so youll want to protect your

logs.

3. Avoid storing secrets. Design around storing secrets. If necessary, sometimes they can beavoided by storing them after using a one-way hash algorithm.

4. Avoid storing sensitive data in the Web space. Anything exposed to the public Internet isconsidered web space. Sensitive data stored in a location that might be compromised by

any member of the public places it at much higher risk.

5. Back up and regularly analyze log files. Some attacks can occur over time. Regular analysisof logs will allow you to recognize with sufficient time to address them. Performing regularbackups lowers the risk of an attacker covering his tracks by deleting logging of his activities.

6. Be able to disable accounts. The ability to reactively defend an attack by shutting out a usershould be supported through the ability to disable an account.

7. Be careful with canonicalization issues. Predictable naming of file resources is convenientfor programming, but is also very convenient for malicious parties to attack. Application

logic should not be exposed to users in this manner. Instead, you use file names derived

from the original names or fed through a one-way hashing algorithm.

8. Catch exceptions. Unhandled exceptions are at risk of passing too much information to theclient. Handle exceptions when possible.

9.

Centralize your input and data validation. Input and data validation should be performedusing a common set of code such as a validation library.

10.Consider a centralized exception management framework. Exception handling frameworksare available publically and provide an established and tested means for handling

exceptions.

11.Consider authorization granularity. Every object needs to have an authorization controlthat authorizes access based on the identity of the authenticated party requesting access.

Fine grained authorization will control access to each resource, while coarse grained

authorization will control access to groups of resources or functional areas of the

application.

12.Consider identity flow. Auditing should be traceable back to the authenticated party. Takenote of identity transitions imposed by design decisions like impersonation.

13.Constrain input. Limit user input to expected ranges and formats.14.Constrain, reject, and sanitize your input. Constrain, reject and sanitize should be primary

techniques in handling input data.

15.Cycle your keys periodically. Expiring encryption keys lowers the risk of stolen keys.


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16.Disable anonymous access and authenticate every principle. When possible, require allinteractions to occur as an authenticated party as opposed to an anonymous one. This will

help facilitate more effective auditing.

17.Do not develop your own cryptography. Custom cryptography is not difficult for experts tocrack. Established cryptography is preferred because it is known to be safe.

18.Do not leak information to the client. Exception data can potentially contain sensitive dataor information exposing program logic. Provide clients only with the error data they need

for the UI.

19.Do not log private data such as passwords. Log files are an attack vector for maliciousparties. Limit the risk of their being compromised by not logging sensitive data in the log.

20.Do not pass sensitive data using the HTTP-GET protocol. Data passed using HTTP GET isappended to the querystring. When users share links by copying and pasting them from the

browser address bar, sensitive data may also be inadvertently passed. Pass sensitive data in

the body of a POST to avoid this.

21.Do not rely on client-side validation. Any code delivered to a client is at risk of beingcompromised. Because of this, it should always be assumed that input validation on the

client might have been bypassed.

22.Do not send passwords over the wire in plaintext. Authentication informationcommunicated over the wire should always be encrypted. This may mean encrypting the

values, or encrypting the entire channel with SSL.

23.Do not store credentials in plaintext. Credentials are sometimes stored in applicationconfiguration files, repositories, or sent over email. Always encrypt credentials before

storing them.

24.Do not store database connections, passwords, or keys in plaintext. Configuration secretsshould always be stored in encrypted form, external to the code.

25.Do not store passwords in user stores. In the event that the user store is compromised, anattack should never be able to access passwords. A derivative of a password should bestored instead. A common approach to this is to encrypt a version of the password using a

one-way hash with a SALT. Upon authentication, the encrypted password can be re-

generated with the SALT and the result can be compared to the original encrypted

password.

26.Do not store secrets in code. Secrets such as configuration settings are convenient to storein code, but are more likely to be stolen. Instead, store them in a secure location such as a

secret store.

27.Do not store sensitive data in persistent cookies. Persistent cookies are stored client-sideand provide attackers with ample opportunity to steal sensitive data, be it through

encryption cracking or any other means.28.Do not trust fields that the client can manipulate (query strings, form fields, cookies, or

HTTP headers). All information sent from a client should always be assumed to be

malicious. All information from a client should always be validated and sanitized before it is

used.

29.Do not trust HTTP header information. Http header manipulation is a threat that can bemitigated by building application logic that assumes HTTP headers are compromised and

validates the HTTP headers before using them.


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30.Encrypt communication channels to protect authentication tokens. Authentication tokensare often the target of eavesdropping, theft or replay type attacks. To reduce the risk in

these types of attacks, it is useful to encrypt the channel the tokens are communicated

over. Typically this means protecting a login page with SSL encryption.

31.Encrypt sensitive cookie state. Sensitive data contained within cookies should always beencrypted.

32.Encrypt the contents of the authentication cookies. In the case where cookies arecompromised, they should not contain clear-text session data. Encrypt sensitive data within

the session cookie.

33.Encrypt the data or secure the communication channel. Sensitive data should only bepassed in encrypted form. This can be accomplished by encrypting the individual items that

are sent over the wire, or encrypting the entire channel as with SSL.

34.Enforce separation of privileges. Avoid building generic roles with privileges to perform awide range of actions. Roles should be designed for specific tasks and provided the

minimum privileges required for those tasks.

35.Enforce unique transactions. Identify each transaction from a client uniquely to helpprevent replay and forgery attacks.

36.Identify malicious behavior. Monitoring site interactions that fall outside of normal usagepatterns, you can quickly identify malicious behavior. This is closely related to Know what

good traffic looks like.

37.Keep unencrypted data close to the algorithm. Use decrypted data as soon as it isdecrypted, and then dispose of it promptly. Unencrypted data should not be held in

memory in code.

38.Know what good traffic looks like. Active auditing and logging of a site will allow you knowrecognize what regular traffic and usage patterns are. This is a required step in order to be

able to identify malicious behavior.

39.Limit session lifetime. Longer session lifetimes provide greater opportunity for Cross-SiteScripting or Cross-Site Request Forgery attacks to add activity onto an old session.

40.Log detailed error messages. Highly detailed error message logging can provide clues toattempted attacks.

41.Log key events. Profile your application and note key or sensitive operations and/or events,and log these events during application operation.

42.Maintain separate administration privileges. Consider granularity of authorization in theadministrative interfaces as well. Avoid combining administrator roles with distinctly

different roles such as development, test or deployment.

43.Make sure that users do not bypass your checks. Bypassing checks can be accomplished bycanonicalization attacks, or bypassing client-side validation. Application design should avoidexposing application logic, and segregating application logic into flow that can be

interrupted. For example, an ASPX page that performs only validations and then redirects.

Instead, validation routines should be tightly bound to the data they are validating.

44.Pass Forms authentication cookies only over HTTPS connections. Cookies are at risk oftheft and replay type attacks. Encrypting them with SSL helps reduce the risk of these types

of attacks.


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45.Protect authentication cookies. Cookies can be manipulated with Cross-Site Scriptingattacks, encrypt sensitive data in cookies, and use browser features such as the HttpOnly

cookie attribute.

46.Provide strong access controls on sensitive data stores. Access to secret stores should butauthorized. Protect the secret store as you would other secure resources by requiring

authentication and authorization as appropriate.47.Reject known bad input. Rejecting known bad input involves screening input for values that

are known to be problematic or malicious. NOTE: Rejecting should never be the primary

means of screening bad input, it should always be used in conjunction with input

sanitization.

48.Require strong passwords. Enforce password complexity requirement by requiring longpasswords with a combination of upper case, lower case, numeric and special (for example

punctuation) characters. This helps mitigate the threat posed by dictionary attacks. If

possible, also enforce automatic password expiry.

49.Restrict user access to system-level resources. Users should not be touching systemresources directly. This should be accomplished through an intermediary such as the

application. System resources should be restricted to application access.

50.Retrieve sensitive data on demand. Sensitive data stored in application memory providesattackers another location they can attempt to access the data. Often this data is used in

unencrypted form also. To minimize risk of sensitive data theft, sensitive data should be

used immediately and then cleared from memory.

51.Sanitize input. Sanitizing input is the opposite of rejecting bad input. Sanitizing input is theprocess of filtering input data to only accept values that are known to be safe. Alternatively,

input can be rendered innocuous by converting it to safe output through output encoding

methods.

52.Secure access to log files. Log files should only be accessible to administrators, auditors, oradministrative interfaces. An attacker with access to the logs might be able to gleansensitive data or program logic from logs.

53.Secure the communication channel for remote administration. Eavesdropping and replayattacks can target administration interfaces as well. If using a web based administration

interface, use SSL.

54.Secure your configuration store. The configuration store should require authenticatedaccess and should store sensitive settings or information in an encrypted format.

55.Secure your encryption keys. Encryption keys should be treated as secrets or sensitive data.They should be secured in a secret store or key repository.

56.Separate public and restricted areas. Applications that contain public front-ends as well ascontent that requires authentication to access should be partitioned in the same manner.Public facing pages should be hosted in a separate file structure, directory or domain from

private content.

57.Store keys in a restricted location. Protect keys with authorization policies.58.Support password expiration periods. User passwords and account credentials are

commonly compromised. Expiration policies help mitigate attacks from stolen accounts, or

disgruntled employees who have been terminated.


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59.Use account lockout policies for end-user accounts. Account login attempts should have acap on failed attempts. After the cap is exceeded the account should prevent further login

attempts. Lockout helps prevent dictionary and brute force attacks.

60.Use application instrumentation to expose behavior that can be monitored: Applicationtransactions that are more likely to be targeted by malicious interactions should be logged

or monitored. Examples of this might be adding logging code to an exception handler, orlogging individual API calls. By providing a means to watch these transactions you have a

higher likelihood of being able to identify malicious behavior quickly.

61.Use authentication mechanisms that do not require clear text credentials to be passedover the network: A variety of authentication approaches exist for use with web based

applications some involve the use of tokens while others will pass user credentials (user

name/id and password) over the wire. When possible, it is safer to use an authentication

mechanism that does not pass the credentials. If credentials must be passed, it is preferable

to encrypt them, and/or send them over an encrypted channel such as SSL.

62.Use least privileged accounts. The privileges granted to the authenticated party should bethe minimum required to perform all required tasks. Be careful of using existing roles that

have permissions beyond what is required.

63.Use least privileged process and service accounts. Allocate accounts specifically for processand service accounts. Lock down the privileges of these accounts separately from other

accounts.

64.Use multiple gatekeepers. Passing the authentication system should not provide a goldenticket to any/all functionality. System and/or application resources should have restricted

levels of access depending on the authenticated party. Some design patterns might also

enforce multiple authentications, sometimes distributed through application tiers.

65.Use SSL to protect session authentication cookies. Session authentication cookies containdata that can be used in a number of different attacks such as replay, Cross-Site Scripting or

Cross-Site Request Forgery. Protecting these cookies helps mitigate these risks.66.Use strong authentication and authorization on administration interfaces. Always require

authenticated access to administrative interfaces. When applicable, also enforce separation

of privileges within the administrative interfaces.

67.Use structured exception handling. A structured approach to exception handling lowers therisk of unexpected exceptions from going unhandled.

68.Use the correct algorithm and correct key length. Different encryption algorithms arepreferred for varying data types and scenarios.

69.Use tried and tested platform features. Many cryptographic features are available throughthe .NET Framework. These are proven features and should be used in favor of custom

methods.70.Validate all values sent from the client. Similar to not relying on client-side validation, any

input from a client should always be assumed to have been tampered with. This input

should always be validated before it is used. This encompasses user input, cookie values,

HTTP headers, and anything else that is sent over the wires from the client.

71.Validate data for type, length, format, and range. Data validation should encompass theseprimary tenets. Validate for data type, string lengths, string or numeric formats, and

numeric ranges.


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SDL Considerations

For more information on preferred encryption algorithms and key lengths, see the SecurityDevelopment Lifecycle athttp://www.microsoft.com/security/sdl/.
http://www.microsoft.com/security/sdl/http://www.microsoft.com/security/sdl/http://www.microsoft.com/security/sdl/http://www.microsoft.com/security/sdl/


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Design Guidelines for Improving Cloud Application Security

OverviewWhile many of the same security patterns and practices you apply to applications you run on-

premise, also apply to the cloud, you do need to think about how the context changes some

things. For example, running in the cloud means running your applications and data in an

environment where you trade control for economic or technical benefits.

Applications running in the cloud by their nature are Internet facing. Deployment patterns

change including where you run your code, and how it makes calls to other services or

applications. Running in the cloud means thinking in terms of virtualized resources. It also

means restricted access to some underlying system resources. Additionally, it means thinking

about the interfaces you expose, how you protect them, and the communication protocols you

use.

Running in the cloud also means rethinking security context, as well as identity management

and access controls, and considering approaches that allow you to integrate, leverage, and

interoperate with your existing resources or other services or systems in the cloud, or even with

on-premise systems and services.

For a synopsis view of changes to development introduced with Windows Azure, see the

Whats New with Windows Azure Cheat Sheet in the Appendix.

Windows Azure and Windows Identity Framework Impact

The following are points that will help you think about how Windows Azure and how WindowsIdentity Framework may impact your security design:

Claims -- You can use claims for identity management and for access control. Claims alignwell with cloud applications because they allow you to factor out identity management logic

from your application and integrate with identity providers such as an on-premise Active

Directory via Active Directory Federation Services.

VM model and trust -- The Windows Azure security model is centered around strict controlover VMs imposed by two Windows Azure specific trust policies which are defined as full

and partial trust. These policies limit access to system resources to prohibit common attacks

like elevation of privilege. A working knowledge of what level of permissions are available is

required to know which pieces of an existing application can be migrated and which must

be adjusted to work under more restrictive permissions.

For more information on full trust in Azure, seehttp://msdn.microsoft.com/en-

us/library/dd573363.aspxFor more information on partial trust in Azure, see

http://msdn.microsoft.com/en-us/library/dd573355.aspx
http://msdn.microsoft.com/en-us/library/dd573363.aspxhttp://msdn.microsoft.com/en-us/library/dd573363.aspxhttp://msdn.microsoft.com/en-us/library/dd573363.aspxhttp://msdn.microsoft.com/en-us/library/dd573363.aspxhttp://msdn.microsoft.com/en-us/library/dd573355.aspxhttp://msdn.microsoft.com/en-us/library/dd573355.aspxhttp://msdn.microsoft.com/en-us/library/dd573355.aspxhttp://msdn.microsoft.com/en-us/library/dd573363.aspxhttp://msdn.microsoft.com/en-us/library/dd573363.aspx


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Azure Storage and SQL Azure -- Some of the things to think about in Windows Azureregarding data include deciding where to host your data, what will be used to host the data,

and what the means of access to that data will be. You can use on-premise data and expose

it as a service to your Windows Azure application. Data hosting in the cloud can be done

primarily through Windows Azure Storage or SQL Azure. Data exposed to other applications

or services should be exposed as a service (Data as a Service), but data consumed only byyour application has the option of being accessed without a service interface.

Deployment -- Deploying the Windows Azure can potentially mean deploying acrossmultiple data centers that are physically separate. This will influence application design

patterns, deployment, as well as communication between application pieces. Be aware of

your application boundaries, and use resources within the same data center when possible,

and communication options such as internal endpoints when applicable.

Architecture and Design Issues for Cloud Applications

When you design for the cloud, keep the following guidelines in mind:

Factor authentication and authorization logic from application logic. Use claims based authentication to integrate with existing user stores. Know the Windows Azure trust policy restrictions. Consider your storage options: Windows Azure Storage, SQL Azure, Azure Drives. Know the communication changes.

Factor authentication and authorization logic from application logic

Implementing authentication and authorization logic based on claims allows you to decoupleyour application logic from your identity logic. This provides for more secure applications by

standardizing around a common implementation of authentication logic around the WS-*

protocols. Having the identity logic separate makes the application more maintainable too, by

allowing updates or changes to authentication logic that does not impact the application.

Building around the WS-* protocols also provides for better interoperability.

Use claims based authentication to integrate with existing user stores

Established approaches to authentication and authorization are still valid in the cloud, but

claims and Single Sign-On (SSO) approaches provide strong integration with Active Directorybased authentication and federated identity. It is still possible to implement authentication

using ASP.NET forms authentication but this will involve creating a new user store. To leverage

an existing user store, or integrate with foreign user stores or an on-premise Active Directory,

you will want to use the Windows Identity Federation to use the WS-* protocols for a claims

based authentication solution.


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Know the Windows Azure trust policy restrictions

Code operating in a Windows Azure VM will operate with a more restrictive set of permissions.

The default is full trust which still contains a more restrictive set of permissions than an on-

premise solution. Some of the most prominent restrictions include the limited access to the

registry, and some basic file access restrictions as well. Avoid API's that require system level

permissions, or access to Operating System resources. Use internet friendly protocols for

service calls, and internal endpoints or queues for IPC.

Consider your storage options: Windows Azure Storage, SQL Azure, Azure

Drives

Windows Azure Storage and SQL Azure are the 2 primary storage options for Windows Azure

applications. Azure drives offer another option for persisting information, by writing to the

VM's virtual drive, and persisting the drive state to Azure Drives. SQL Azure offers relational

data storage and a host for existing TSQL logic. Windows Azure storage offers a lower cost per

megabyte stored.

Know the communications changes

Working inside of the Windows Azure data centers influences application design, from the

communication standpoint, in a number of ways. VM's are exposed to the public internet as a

sub-domain off of the cloudapp.net domain. This means a singular IP address will represent a

web role, but the Windows Azure load balancer will resolve the traffic to a VM represented by a

virtual IP address. Applications should not be designed with VM instances that depend on

specific IP addresses.

Be aware of network communication inside and outside of the Windows Azure data centers.

You can gain better performance by taking advantage of the higher bandwidth communications

within a data center, as opposed to reaching outside of the data center for services. This

becomes important because the latency introduced at this level can be exploited by attackers in

Denial of Service attacks.

Know that internal endpoints for Windows Azure roles exist that allow roles to perform IPC

within the data center using TCP based protocols. Both web and worker roles can expose

endpoints for tightly bound IPC, whereas Windows Azure Storage queues can be used for

loosely bound IPC. The following diagram represents a typical application of queues to perform

IPC.


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Web RoleLo

adB

alancer

VMs VMs

Worker Role

HTTP /

HTTPs

Storage

Message

Message

Message

Queue

IIS Write Read

Figure 1. Windows Azure Storage queues for IPC Typical model

Potential Application Security Vulnerabilities Summary

Hot Spot Description

Auditing and Logging Attacks made without a trace, unauthorized access to logs or audits, covering

tracks by removing audit or log events.

Authentication Identity spoofing, password cracking, elevation of privileges, and unauthorized

access.

Authorization Access to confidential or restricted data, tampering, and execution of

unauthorized operations.

Communication Eavesdropping, sniffing, replay attacks.

Configuration

Management

Unauthorized access to administration interfaces, ability to update

configuration data, and unauthorized access to user accounts and account

profiles.

Cryptography Access to confidential data or account credentials, or both.

Input and Data

Validation

Attacks performed by embedding malicious strings in query strings, form fields,

cookies, and HTTP headers. These include command execution, cross-site

scripting (XSS), SQL injection, and buffer overflow attacks.

Exception

Management

Denial of service and disclosure of sensitive system level details.

Sensitive Data.

Sensitive Data Confidential information disclosure and data tampering.

Deployment Considerations


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Data Centers and Distribution

Windows Azure data centers exist in pairs for each continental area supported. The Windows

Azure Portal allows you to specify which data center to deploy your application to. This

becomes particularly important for applications that are not deployed as a single package. For

example, if you deploy a web service to one data center, and then deploy an application that

uses that service in a different data center, you will experience more latency than if both are

deployed to the same data center. Also note that network traffic within a single data center will

be at a much higher level of performance than traffic that must reach the public Internet.

Consider the geographic location for your users when deciding which data center(s) to deploy

to. Determine which data center has the best network response times for your users and

deploy your application to this data center. For example, if your users mostly live in Ohio, the

Northern US data center located in Chicago will most likely offer the best response times for

these users. Confirm that network performance is superior from this data center, and deploy to

it.

Deployment packages are typically built from Visual Studio projects. A Visual Studio project can

contain any number of roles. Roles deployed as part of a single deployment package will be

deployed as a group and distributed in the data center in fairly close proximity to provide

optimal performance. The following diagram represents what a deployment in a single data

center might encompass.


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Windows Azure

Web RoleWeb Role Web RoleWeb RoleWeb Role

Presentation Layer

ASP.NET UI

Web Role

Services Layer

Service

Interfaces

80 80

Worker RoleWorker RoleWorker Role

Business Layer

Data Layer

BrowserMobile Rich Client

Silverlight

Front-end

Silverlight

Front-end

Silverlight

Front-end

SQL Azureor

Azure Storage

SQL Azureor

Azure Storage

SQL Azureor

Azure Storage

Figure 2. Single data center deployment application architecture

Locations for SQL Azure and Windows Azure Storage can be specified when establishing theservices. It is beneficial to specify the same data center for your application as you use for your

data.

Keep these things in mind when securing your Windows Azure application, and remember that

it is significantly easier to eavesdrop on traffic on the public Internet than it would be to

compromise security within an Azure data center and sniff traffic inside the data center.

Internal versus External Traffic

Windows Azure meters data transfer for billing. Metering is performed on traffic entering and

leaving the data center, but not inside the data center. Systems comprising of parts that must

communicate between VMs, should be deployed to the same data center to optimize

expenditures.

Be aware of Windows Azure affinity groups. Affinity groups tell Windows Azure to deploy

applications in similar areas within the data center. Doing this will minimize the number of

network hops within a data center and improve network performance for your application.


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Separation of Responsibilities and Deployment Environments

Separation of responsibilities should be considered for any Windows Azure deployment. This

means you should have clear policies defined for the roles of administrator, release manager,

developer, tester and any other appropriate role.

The Windows Azure Portal is accessible via 2 methods. A user interface that requires a Live ID to

access, and deployment APIs that require a deployment certificate. Multiple deployment

certificates can be added to a Windows Azure account. These certificates can be added to

Visual Studio and allow multiple distinct parties to deploy from Visual Studio to Windows Azure.

Because the Windows Azure Portal access is controlled by Live ID and deployment certificates,

policies should be established and include proper management and distribution of both the Live

ID and the deployment certificates. Developers should not be in charge of deployment, nor

management of the Windows Azure service. Test environments should be deployed separately

from production and staging environments.

Note that separation of deployment rights between staging and production environments will

prohibit the use of the Virtual IP (VIP) swapping feature in the Windows Azure Portal. This

feature allows you to instantly make your staging environment live. The VIP swapping feature

requires that both the deployment and staging deployments be under the same Windows

Azure Account.

Auditing and LoggingAuditing and logging involves the handling of security related events. Processes for storing the

events, monitoring them, and auditing the logs are covered here. Windows Azure introducessome additional considerations in this area due to changes in the logging systems and methods

for persisting the logs to permanent storage. Windows Azure applications will also need to build

methods for monitoring application health and providing notifications.

The following practices improve your application's auditing and logging:

Protect your logs. Consider identity flow. Audit and log access across the application. Sanitize data before logging. Back up and analyze logs regularly.

Protect your logs.

Auditing and logging in Windows Azure must be performed to a location that can be secured

and persisted. Event logging can be performed to Windows Azure's Monitoring Data Service.

Logs should then be persisted into a secure storage location such as Windows Azure Storage.

When persisting logs to storage, be sure to implement strong authentication and authorization


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against that storage location. Also be aware that access to Windows Azure storage will be via

the RESTful interfaces and should therefore be secured over SSL.

For more information about auditing and logging, see the Security Best Practices for Developing

Windows Azure Applications at

http://www.microsoft.com/downloads/details.aspx?displaylang=en&FamilyID=0ff0c25f-dc54-4f56-aae7-481e67504df6.

Consider identity flow.

In Windows Azure, application architectures will commonly flow identities through a common

channel. Examples of this would be users authenticating against a web site, and data access to

Windows Azure Storage occurring over a common connection, or a common connection string

for SQL Azure. Be aware of this identity flow, and be sure to have a way of mapping data access

back to the authenticated user. This might be accomplished by passing a user identifier with the

data access and storing this with the transaction. Be sure to protect the identifier with a one-way hash if it is not passed over an encrypted channel.

Audit and log across the application.

Audits and logged events should occur at all levels of the application. When implementing

logging, be aware of the implications of excessive logging. Excessive logging can lead to

degradation of performance and might be exploited to cause a failure in the service in a Denial

of Service attack. In cases where extensive logging may be required for debugging purposes,

consider implementing logging levels that can be configured through an administrative

interface. This allows you to obtain detailed logs when required, but not degrade performance

when debugging isnt being performed.

Be sure to log at all locations in code where authentication or authorization takes place.

Additionally, be sensitive to transitions in identity such as using a common identity to connect

to a web service such as with a WCF binding using a server certificate for service authentication.

Review your application logic flow for key events, and be sure to log these events. Be sure to

log both success and failure events.

Include enough information in your logs to reconstruct the user interaction across all levels of

the site. With a site that is potentially logging events from several different requests at thesame time, it is important to be able to associate log events together. A common means of

accomplishing this is to assign a log identifier to be included with all logged events for a

particular transaction. Doing this allows you to filter the log based on an id to reconstruct the

event flow. Do not use a session id or other sensitive information for this identifier.


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Sanitize data before logging.

Logged information should not contain any sensitive information or information that allows an

attacker to determine the logic of the application. Assume that an attacker can gain access to

the logs, and ensure that information that reaches the logs does not contain anything the

attacker can use. Logged information should be passed through a sanitization process before

being sent to the log. This process should strip out sensitive information such as credentials,

authentication tokens, file names, and application function names (such as in a call stack).

Back up and analyze log files.

Evaluate your strategy for maintaining historical log information. Windows Azure Storage can

provide up to 100TB of storage for logging data and is implicitly backed up in accordance with

the Windows Azure SLA. If you establish an archival process, be sure that the archives also have

a backup process in place.

Perform regular analysis on your log files to recognize normal usage patterns. This allows you to

quickly recognize irregular patterns which might be attacks.

AuthenticationAuthentication involves verifying the identity of parties accessing your application or services.

In Windows Azure, standard username and password credential based systems are possible, as

well as claims based identity frameworks that are well suited for cloud implementations.

The following practices improve your application's authentication:

Do not send passwords over the wire in plaintext. Do not store passwords in user stores. Separate public and restricted areas. Use established password policies.

Do not send passwords over the wire in plaintext.

Authenticating against a user id and password combination does not require these credentials

to be passed over the wire in order to authenticate. Use established practices to convert the

credentials into a secure form before transmitting them over the wire. By leveraging a claims

based authentication system based on WS* and Windows Identity Federation, you gain this

benefit. A claims based authentication system will authenticate by passing tokens over the wireinstead of credentials.

If you use an alternate authentication system, you should also avoid transferring credentials

over the wire. A typical approach is to perform a one-way hash on the password, and generate

the same hash on the server-side and comparing the results.


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Be aware of using email to distribute passwords or as part of your password reset procedures.

Instead of passing the user credentials in email, consider an alternate approach allowing users

to use alternate means to identify themselves (such as secrets) in the UI and reset the

password.

Do not store passwords in user stores.

This policy strongly relates to not sending passwords over the wire. Passwords should not be

stored in the user store or database. Instead, one-way hash the password using a SALT (a

cryptographically strong random number) and store the SALT and the hashed value in the user

store. These 2 items allow you to repeat the procedure when a user authenticates and compare

the hashed results.

Use established password management policies.

Password policies are established to lessen the vulnerability to dictionary or brute-force attacksagainst authentication. These policies include:

Require strong passwords. Strong password policies should encompass minimum passwordlength, and use of alpha-numeric and special characters.

Enforce requirements when using a passphrase. Passphrases should also have minimumrequirements for number of characters, and potentially special characters too.

Enforce password expiration periods. Use account lockout policies for end-user accounts. Support administrative disabling of accounts. Maintain a password history, but do not store the actual password as described above.

AuthorizationAuthorization covers the control over accessing resources within your application. In Windows

Azure these resources also include controlling access to Windows Azure Storage, SQL Azure and

WCF services. Traditional Role Based Authorization Control (RBAC) and claims based systems

are covered here.

The following practices improve your application's authorization:

Use multiple gatekeepers.

Consider authorization granularity. Restrict user access to system-level resources. Use RESTful interfaces carefully Separate public and restricted areas.


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Use multiple gatekeepers.

You should have one entry point that is secured. Within that channel, you might setup multiple

gatekeepers, so that in the event there is a compromise, you can slow an attacker down, by

creating more hurdles to jump through - or multiple choke-points for your application.

However, you have to balance the complexity of multiple gatekeepers with keeping your design

simple and easy to manage.

Consider authorization granularity.

When using a Role Based Authorization Control (RBAC) approach, ensure that the roles you

define are distinct enough to allow explicit access control without affecting other roles. For

example, if you wish to grant access of administration interfaces to administrators, other roles

such as database administrators should not also receive access. Careful analysis of your

application's users is necessary to determine the roles necessary and avoid enforce proper

separation of privileges between roles.

Restrict user access to system-level resources.

Windows Azure web roles and worker roles operate with the policy restrictions defined by

Windows Azure Partial Trust and full trust levels. Due to the restrictions defined by these

policies, access to system-level resources is prohibited and therefore implicitly supported by

the Windows Azure environment.

For more information on trust policy restrictions can be found at

http://msdn.microsoft.com/en-us/library/dd573355.aspx.

Use RESTful interfaces carefully

RESTful interfaces are designed to convey information about their logical function and the data

or information they return in the URL. The nature of this design makes it easy to inadvertently

expose application logic or structure to attackers. When implementing RESTful interfaces, be

sure to implement authorization against the interfaces with AppFabric Access Control whenever

possible. If authorization is not possible, it is recommended to only expose data for reading

with RESTful interfaces. Operations against the data should be accessed through an authorized

interface.

When designing RESTful interfaces, follow established practices that dictate exposing data can

be performed with HTTP GET requests, whereas modification of data via Create, Update or

Delete operations should be done using an HTTP POST.
http://msdn.microsoft.com/en-us/library/dd573355.aspxhttp://msdn.microsoft.com/en-us/library/dd573355.aspxhttp://msdn.microsoft.com/en-us/library/dd573355.aspx


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Separate public and restricted areas.

For web applications it is important to separate public and restricted areas of the application.

Use this approach over securing files by name in the web.config tag. By

securing pages by directory, there are no additional steps necessary to secure the page after

placing it in the secure directory. This lowers the chance that an error could be made due to

failure to make settings in a configuration file like the web.config.

CommunicationCommunication encompasses how data is transmitted over the wire. This includes encrypting

the entire channel for applications with SSL, but also security web services with transport or

message based security. Certificate and key management for SSL are also topics covered here.

The following practices improve your application's communication security:

Windows Azure Storage should not use container names based on user input. Protect sensitive data over the wire. Periodically change your keys. Optimize communication security over performance. Check for accidental information disclosure.

Windows Azure Storage should not use container names based on user

input.

Windows Azure Storage is accessed using RESTful interfaces. This can place data at risk of

injection attacks if the attacker is able to affect the URI being called during data operations.

Because of this, it is recommended avoid using user input for Windows Azure Storage names

when possible. In the event that user input is needed, be sure to sanitize the user input byencoding it before using it.

For more information on this, see Security Best Practices for Developing Windows Azure

Applications at

http://www.microsoft.com/downloads/details.aspx?displaylang=en&FamilyID=0ff0c25f-dc54-

4f56-aae7-481e67504df6.

Protect sensitive data over the wire.

Sensitive information such as authentication information, personal information, or other HighBusiness Impact (HBI) data should never be transferred over the wire in clear-text. Web

applications should encrypt the channel with SSL, or encrypt data items before sending them

over the wire. WCF services should protect sensitive data with either message security or

transport security.


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Periodically change your keys.

In Windows Azure, SSL encryption relies on X509 certificates uploaded to the Windows Azure

portal administration interface. These certificates are used to encrypt the SSL channel and may

also be used as keys for other encryption such as RSA. To help

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