The Top 10 Internet Security Vulnerabilities – A Primer

ITTIP Seminar Copyright 2001 R.C.Marchany 1

The Top 10/20 Internet Security Vulnerabilities – A Primer

Randy Marchany

VA Tech Computing Center

Blacksburg, VA 24060

[email protected]


Introduction This presentation is designed to give you a

brief overview of the top 10 most critical Internet Security threats.

These aren’t the only threats….just the most common at the moment.

Hopefully, we’ll eliminate these threats and create a new list next year.

The Top 10 and Top 20 documents are in Appendix A of this presentation.


Introduction We’ll review the original Top 10 list first We’ll review the new items in the Top

20 We’ll also provide a list of common

ports to filter or monitor.


Why Are We Vulnerable? Computer systems and programs have

become more complex in the past 25 years. Quality control hasn’t been able to keep up

due to market pressures, programming skill deficiencies, etc.

Most of these programs/systems are based on code that was never intended to be “production” quality.They were “proof of concept” programs that became the basis of production systems.


So Many Systems, Not Enough Time….. 2.3 million hosts are connected to the Net

each month. There aren’t 2.3 million sysadmins. Something has to give….

Unfortunately, it’s the sysadmin. Not enough training, too many conflicting

demands on their time. The Prime Directive: Keep the system up! Patch the system? When I have time….


Hacking = Rocket Science? Not! Any good hacker can write the attack

tool. The real skill is making so easy to use that a CEO could launch the attack.

There are lots of hacker WWW sites where you can get these tools. These sites try to outdo each other by designing the best, baddest, user-friendly site.


Why Are the Attacks Successful? We didn’t close all the doors because

we’re too busy doing “real” stuff. If the hackers got caught, we didn’t punish

them. It would be too embarrassing to admit we got hit. Our Incident Response Plans were inadequate.


Why Are the Attacks Successful? The attack designers studied (cased)

the target code carefully. A lot of attacks are based on Buffer

Overflows. Example: a program expects 80 input

characters max. You give it 5000 characters. How does the code handle it?


Some Pointers About the Lists Each item in the list is divided into 4

parts A description of the vulnerability The systems affected by the vulnerability A CVE number identifying the vulnerability Some suggested corrections


Some Pointers about the Lists What’s a CVE number?

CVE = Common Vulnerabilities & Exposures reference number that is used to uniquely identify a vulnerability.

It’s like the Dewey Decimal #’s that are used in the library. You can go to any library and find the same book using the same Dewey catalog number

CVE’s does the same for vulnerabilities.


Some More Pointers about the Lists Ports to block/monitor at the firewall are

provided at the end of the Top 20 list. Remember this only works for EXTERNAL

attacks. Internal attacks need additional security measures.


Some More Pointers about the Lists Automated Scanning for the Top 20

SARA – freeware scanning tool designed specifically for this. See http://www.cisecurity.org

Commercial scanners are becoming available. Links to ICAT Vulnerability Index

Each entry is linked to the NIST ICAT indexing service. ICAT entries contain a short description of the vulnerability and other info.


Item #1: BIND All Internet systems have a hostname and an

IP address. Every home is known by its address and who lives

in it. “hey, is that Randy’s house?” “Yeah, it’s at 24 Main St.”

“Randy’s house” = hostname “24 Main St.” = IP address

BIND (Berkeley Internet Domain) maps hostnames to IP addresses. It’s the set of “phone books” of the Internet.


Item #1: BIND

Every network needs a couple of systems that run BIND. They’re called nameservers.

Old versions of BIND have security holes.The nameservers aren’t always up-to-date. They were when they were installed but that was years ago. It works so why fix it? Right? Wrong!


Item #1: BIND The Danger:

Hackers get full control of the nameserver and can use it for anything they want.

A Solution Make sure your version is higher than

BIND 8.2.2 patch level 5


Item #2: CGI Scripts CGI = Common Gateway Interface It’s the language that programmers use to

display and read your input to a WWW based form.

Not everyone knows how to use it so WWW server vendors supply examples.

The examples have security holes in them. Some CGI programmers haven’t checked their code.


The Second Item – CGI Scripts All Web servers could be affected by this

“feature”. The Danger

Your WWW pages could be changed a la DOJ, CIA, FBI, Valujet.

Your WWW server could be used to attack other sites

A Solution Remove unsafe CGI scripts from the WWW

server


Item #3: Remote Procedure Calls (RPC) RPC allows a computer to run a program on

another computer. It’s used by computers that share files

between them. Many client – server systems depend on the

use of RPC calls. Unix systems (Solaris, AIX, HP-UX, Linux,

Tru64, Irix) were primarily affected but any computer that uses the RPC subsystem is vulnerable


Item #3: Remote Procedure Calls (RPC) The Danger:

Older versions of RPC have security weaknesses that allow hackers to gain full control of your computer(s).

A Solution Disable the RPC services if you don’t use

them Install the latest vendor patches


Item #4: Microsoft Internet Information Server (IIS) Windows NT and Windows 2000 Web

servers use IIS to support web services. IIS has a component called Remote

Data Services (RDS) that could allow a hacker to run remote commands with administrator privileges.

Code Red, NIMDA


Item #4: Microsoft Internet Information Server (IIS) The Danger:

A hacker can run commands on another system without having to access it directly.

A Solution: Read the Microsoft technical bulletins that

describe how to fix the problem


Item #5: Sendmail Weakness Sendmail is one of the original Internet email

programs. It was a graduate programming project that

was never designed to work in a “production” environment.

It became the defacto standard. Pre-version 8.10 had security problems

Some vendors still ship Sendmail v5.65! Most vendors shipped their systems with these

older versions.


Item #5: Sendmail Weakness The 1988 Internet Worm exploited a problem

in sendmail.There are a lot of systems that still run that version of sendmail. Why? It works!

The Danger: Hackers can run commands on your systems

without ever logging into your system. Hackers can take over your machine.

A Solution: Update to the latest version of sendmail


Item #6: sadmind and mountd Sadmind is used by Solaris applications to

run distributed sysadmin operations. It executes the request on the server from a client program. Sounds like RPC? It is.

Mountd controls file sharing across the network using NFS. This is the program that “attaches” a remote disk to your computer.


Item #6: sadmind and mountd The Danger:

Hackers can cause these programs to give them access to root. They can take over your machine.

This was one of the primary ways hackers used to set up the systems used in the recent DDOS attacks against Yahoo, CNN and other sites.

A Solution: Install the latest vendor patches for sadmind and

mountd.


Item #7: Global File Sharing You can share files between computers

using tools like Network Neighborhood (Windows), AppleShare(Macintosh) or NFS(Unix).

By default, the access is read-write.


Item #7: Global File Sharing Anyone on the same network could

access your files. In the old days, the network was small but now the network is the Internet so anyone anywhere in the world could access your files if you let them.

The problem is that you don’t always know that you’re letting them.


Item #7: Global File Sharing This is a real danger to homes that have

direct connect modems. The Danger:

People can get access to your personal data, for example, your checking account data (if you use MSMoney), your email, etc.

A Solution: Make sure you know what you’re sharing. Make sure you know who’s sharing the data with

you.


Item #8: User Accounts with No Passwords Some systems come with demo or

guest accounts with no passwords or well known passwords.

The initial/default password for VMS system manager account, SYSTEM was MANAGER. The initial password for the Field Service account, FIELD, was SERVICE.


Item #8: User Accounts with No Passwords People forgot to change these

passwords. The first thing hackers do is check to

see if the defaults passwords were changed. Why waste a lot of effort if the door is unlocked?


Item #8: User Accounts with No Passwords The Danger:

Someone can get complete control of your system. Someone can get access to your system via a

general accounts and then run exploit tools on your systems to get full control of your system.

A Solution: Change your root, administrator passwords before

the systems goes into production. Run a password checking program to discover who

has weak passwords on your system. Do it before the hackers do!


Item #9: IMAP, POP Vulnerabilities IMAP and POP are two common email

protocols that provide additional features to email users.

They allow users to access their email accounts from anywhere on the Internet.


Item #9: IMAP, POP Vulnerabilities Firewalls usually allow email using

these services to pass through the firewall.

Quality control of the software is inconsistent most of the time.


Item#9: IMAP, POP Vulnerabilities The Danger:

Hackers can gain access to your internal network if they can subvert IMAP or POP mail server systems.

If successful, they gain complete control of your system.

A Solution: Make sure you’ve installed the latest patches. Run the services on your mail servers only.


Item #10: SNMP Vulnerabilities Simple Network Management Protocol

(SNMP) is used by network managers to monitor the status, performance and availability of the network.

The Net Mgrs can remotely manage their routers, printers, systems using SNMP.


Item #10: SNMP Vulnerabilities SNMP has very weak authentication.

Its default “password” is “private”. Everyone knows this.


Item #10: SNMP Vulnerabilities The Danger:

Hackers can gain control of network devices such as routers. They could shut them down.

They can map your network w/o your knowledge. A Solution:

Pick strong community strings (passwords) for your SNMP devices.

Make the MIBs read only.


Summary Most of the successful system and network

attacks exploit a small set of vulnerabilities. The Top 10 list briefly describes this set of

vulnerabilities and gives you references to learning more about them.

More importantly, it gives you some suggested fixes for the problem.

Our individual security depends on our mutual security.


The SANS/FBI Top 20 List

If we had fixed the top 10, there wouldn’t be a top 20.


Top 20 List Organization Vulnerabilities that affect all systems

Unix/Linux Windows Mac Mainframes

Windows Vulnerabilities Unix Vulnerabilities


Top 20 Summary General – Affects all Systems

G1: Default OS Installations G2: Accounts with Weak or No Passwords G3: Non-existent or Incomplete Backups G4: Large Number of Open Ports G5: Incorrect Ingress/Egress Packet Filtering G6: Non-existent or Incomplete Logging G7: Vulnerable CGI Programs


Top 20 Summary Windows

W1: Unicode Vulnerability W2: ISAPI Extension Buffer Overflows W3: IIS RDS Exploit W4: Unprotected NETBIOS Shares W5: Null Sessions W6: Weak Hashing in SAM (LM Hash)


Top 20 Summary Unix

U1: RPC buffer Overflows U2: Sendmail Vulnerabilities U3: BIND U4: R Commands U5: LPD Buffer Overflow U6: sadmind mountd Buffer Overflow U7: Default SNMP


G1: Default OS Installations OS and application installs are not

configured for security Vendor Philosophy

Better to enable all functions than require the user to turn them on individually.

Convenience vs. Security: Who wins?


G1: Default OS Installations System Impacted

All Unix, Linux, Windows, MacOS are vulnerable to some degree. Windows, SGI are more open than normal.


G1: Default OS Installations Are you vulnerable?

If you use default vendor installation programs then you are vulnerable.

Extra extra service/tool installed that is not needed is another window into your system.


G1: Default OS Installations How to protect?

Remove unnecessary software/services asap.

Install minimum then add. This can be automated using Minimum Installation guidelines.

Use the CIS Security Benchmark tools for your OS.


G3: Non-existent, Incomplete Backups Recovery from an incidents requires up-to-

date backup. Have you verified the backups actually work? Offsite? 9/11 proved this. How long does it take to RESTORE the data?

What is the data xfer rate of your tape drives? Systems Impacted

Any critical system


G3: Non-existent, Incomplete Backups Am I vulnerable?

Check backup procedures. Is the backup interval acceptable? Are the systems being backup up

according to procedure? Off site storage? Procedures? Restoration tested and verified?


G3: Non-existent, Incomplete Backups How to Protect

Daily backups Monthly backups should be verified.


G4: Large Number of Open Ports The more ports open, the more ways to

get into the system. Related to Default OS install

vulnerability. Systems Impacted

Any system that used a vendor default installation program.


G4: Large Number of Open Ports Am I vulnerable?

Use netstat command to list open ports. Run a port scanner (nmap, Nessus)

against your system. Match open ports to legitimate services

provided by the machine. If no match, then it’s an unnecessary service.


G4: Large Number of Open Ports How to protect myself

Unix: modify /etc/inetd.conf Windows NT/2000 : use fport from www.

foundstone.com to list the ports. Windows XP: netstat –o command


G5: Incorrect Ingress/Egress Router Filters Description

IP spoofing hides the attacker. Numerous attacks (Smurf, mail forgery)

use this technique. Systems Impacted

Unix, Windows, Mac, Routers


G5: Incorrect Ingress/Egress Router Filters Am I vulnerable?

Send a spoofed packet and see if it’s blocked and logged.


G5: Incorrect Ingress/Egress Router Filters How to Protect

Incoming packets must not have SRC of your internal network. It must have a DST of your internal network.

Outbound packets must have a SRC of your internal network. Outbound packets must not have a DST of your internal net.

No packet should have SRC/DST of a private address or address listed in RFC1918..

Block any source routed packet with IP options set


G6: Non-existent, Incomplete Logging Description

You can’t detect an attack if you don’t know what’s going on your network.

Logs are business records! Systems Impacted

All system and network devices


G6: Non-existent, Incomplete Logging Am I vulnerable?

Are there logs for the critical assets? How to Protect?

Set up local and central logging. Save on CD or other Read-Only device.


W1: Unicode – Web Server Traversal Description

Unicode provides a unique number for every character regardless of the the platform, program or language.

You can send IIS a carefully constructed URL with an invalid Unicode sequence that will let an attacker see any file anywhere on the system.

You can run programs as well.


W1: Unicode – Web Server Traversal Systems Impacted

Windows NT 4.0 with IIS 4.0 Windows 2000 server with IIS 5.0 with no

SP2 CVE-2000-0884


W1: Unicode – Web Server Traversal Am I vulnerable?

Unpatched version of IIS? Yes! Did you install MS00-057, MS00-078,

MS00-086, MS00-026, MS00-044, SP2? Yes, then ok.


W1: Unicode – Web Server Traversal Enter: http://victim/scripts/..%c0%af../

winnt/system32/cmd.exe?/c+dir+c:\ If you removed scripts dir, then it’ll fail.

Replace scripts with whatever you named your script directory.


W1: Unicode – Web Server Traversal How to Protect

Install latest Microsoft patches. See http://www.microsoft.com/technet/security/bulletin/MS00-78.asp

Install IIS lockdown tool if you want. Don’t use IIS for critical functions, IMHO.


W2: ISAPI Extension Buffer Overflows Description

Several ISAPI extensions are installed by default when you install IIS. This allows developers to extend IIS by using DLLs.

Several DLLs, idq.dll, have errors that allow buffer overflow attacks.

This lets an attacker take full control of your IIS server.


W2: ISAPI Extension Buffer Overflows Systems Impacted

Windows 2000 running Index Server 2.0, Indexing Service

Windows 2000 server, Adv. Server, Server Data Center Edition, Professional


W2: ISAPI Extension Buffer Overflows Am I vulnerable?

SP2 installed? No, then you are. Installed MS01-023, MS01-033, MS01-044,

MS01-033, MS01-044, NT4.0 Security Roll-up Package? Yes, then ok.

How to Fix Install latest patches from Microsoft. Unmap unnecessary ISAPI extensions


W5: Null Session Connections Description

Null Session (anonymous login) lets you get info over the net about shares, etc. When 1 machine needs something from another, it uses the local SYSTEM (LocalSystem, W2K) account to open a null session to the remote system. Hackers can use Null logins to gain access to SYSTEM.

This has no password.


W5: Null Session Connections

Systems Impacted Windows NT 4.0, Windows 2000

Am I vulnerable? Go to http://grc.com and click on the

ShieldsUP link to see your system’s SMB exposure.


W5: Null Session Connections

How to Protect Needed for Domain Controllers Block TCP/UDP 139, 445 on the network Never allow Internet users to access any

internal DC.


W6: Weak Hashing in SAM Description

LAN Manager passwords have very weak encryption.

LM passwords are truncated to 14 characters, padded with spaces to 14 characters, converted to all Upper case, split into 2 seven character pieces.

Crackers only have to do 2 upper case seven characters passwords.


W6: Weak Hashing in SAM Systems Impacted

Windows NT, Windows 2000 Am I vulnerable?

Running default installation of NT or W2K? Yes because LM is created by default.


W6: Weak Hashing in SAM How to Protect?

Disable LAN Manager Use NTLMv2 (version 2 LM) Read Technet article “ How to Disable LM

Authentication on Windows NT [Q147706]


U4: R Commands Description

If a user logins from a trusted system, then no password is needed to gain access to your system.

rlogin, rsh, rcp Used by Network Appliance vendors with

no concept of security. Systems Impacted

Any Unix/Linux system


U4: R Commands Am I vulnerable?

Look for .rhosts, /etc/hosts.equiv files. If there, then yes.

How to Protect Disable r-command in /etc/inetd.conf. Fire any one who wants to use it for they

have no concept of security.


U5: LPD Description

The in.lpd program provides local printer services for Unix users.

It listens on port 515 for incoming requests but has a buffer overflow vulnerability allowing root access.

Systems Impacted Solaris 2.6-8 Linux


U5:LPD Am I vulnerable?

Are you running unpatched version of lpd? Yes, then you are.

How to Protect Install latest Solaris or Linux patches. Disable print service in /etc/inetd.conf Block access to port 515 Install TCP Wrappers, Portsentry


Common Vulnerable Ports Common ports probed/attacked Block or log all access to these ports as

necessary. Login services

telnet: 23/tcp FTP: 21/tcp NetBIOS: 139/tcp Ssh: 22/tcp r-commands: 512-514/tcp

RPC/NFS Portmap/rpcbind: 111/tcp/udp NFS: 2049/tcp/udp lockd: 4045/tcp/udp


Common Vulnerable Ports NetBIOS: 135/tcp/udp, 137/udp, 138/udp,

139/tcp, 445/tcp/udp X-Windows: 6000-6255/tcp DNS: 53/udp, LDAP: 389/tcp/udp Mail

SMTP: 25/tcp POP: 109/tcp, 110/tcp IMAP: 143/tcp

WWW HTTP: 80/’tcp SSL:443/tcp


Common Vulnerable Ports Small Services

Ports < 20/tcp/udp, Time: 37/tcp/udp Miscellaneous

TFTP: 69/udp finger: 79/tcp NNTP: 119/tcp NTP: 123/tcp LPD: 515/tcp syslog: 514/udp SNMP: 161/tcp/udp, 162/tcp/udp BGP: 179/tcp

SOCKS: 1080/tcp ICMP:

Block incoming echo requests, outgoing echo reply, time exceeded, destination unreachable. This breaks ping.


Summary You won’t eliminate all of your exposure by

closing these 20 holes. Constant vigilance and awareness is the best defense.

The consequences of failure could drive your company out of business.

There’ll be another top 20 items to inspect in the future but at least we got rid of these items.

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The Top 10 Internet Security Vulnerabilities – A Primer

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