The Top 10/20 Internet
Security Vulnerabilities – A
Primer
Randy Marchany
VA Tech Computing Center
Blacksburg, VA 24060
marchany@vt.edu
ITTIP Seminar
Copyright 2001 R.C.Marchany
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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.
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Copyright 2001 R.C.Marchany
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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.
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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.
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So Many Systems, Not
Enough Time…..

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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….
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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, userfriendly site.
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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.
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Why Are the Attacks
Successful?

The attack designers studied (cased)
the target code carefully.

A lot of attacks are based on Buffer
Overflows.

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Example: a program expects 80 input
characters max. You give it 5000 characters.
How does the code handle it?
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Some Pointers About the Lists

Each item in the list is divided into 4
parts
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A description of the vulnerability
The systems affected by the vulnerability
A CVE number identifying the vulnerability
Some suggested corrections
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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.
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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.
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Some More Pointers about the
Lists

Automated Scanning for the Top 20


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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.
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Item #1: BIND

All Internet systems have a hostname and an
IP address.

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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.
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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!
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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
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Item #2: CGI Scripts

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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.
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The Second Item – CGI
Scripts

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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
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Item #3: Remote Procedure
Calls (RPC)

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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
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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
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Item #4: Microsoft Internet
Information Server (IIS)
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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
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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
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Item #5: Sendmail Weakness

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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.
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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
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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.
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Item #6: sadmind and mountd

The Danger:


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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.
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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.
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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.
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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.
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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.
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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?
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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!
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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.
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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.
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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.
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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.
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Item #10: SNMP
Vulnerabilities


SNMP has very weak authentication.
Its default “password” is “private”.
Everyone knows this.
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Item #10: SNMP
Vulnerabilities
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The Danger:

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
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.
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Summary

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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.
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The SANS/FBI Top 20 List
If we had fixed the top 10, there
wouldn’t be a top 20. 
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Top 20 List Organization

Vulnerabilities that affect all systems
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Unix/Linux
Windows
Mac
Mainframes
Windows Vulnerabilities
Unix Vulnerabilities
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Top 20 Summary
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General – Affects all Systems
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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
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Top 20 Summary
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Windows
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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)
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Top 20 Summary

Unix
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U1: RPC buffer Overflows
U2: Sendmail Vulnerabilities
U3: BIND
U4: R Commands
U5: LPD Buffer Overflow
U6: sadmind mountd Buffer Overflow
U7: Default SNMP
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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? 
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G1: Default OS Installations

System Impacted

All Unix, Linux, Windows, MacOS are
vulnerable to some degree. Windows, SGI
are more open than normal.
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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.
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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.
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G3: Non-existent, Incomplete
Backups

Recovery from an incidents requires up-todate 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
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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?
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G3: Non-existent, Incomplete
Backups

How to Protect


Daily backups
Monthly backups should be verified.
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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.
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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.
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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
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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
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G5: Incorrect Ingress/Egress
Router Filters

Am I vulnerable?

Send a spoofed packet and see if it’s
blocked and logged.
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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
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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
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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.
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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.
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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
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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.
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W1: Unicode – Web Server
Traversal

Enter:
http://victim/scripts/..%c0%af../winnt/sys
tem32/cmd.exe?/c+dir+c:\

If you removed scripts dir, then it’ll fail.
Replace scripts with whatever you named
your script directory.
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W1: Unicode – Web Server
Traversal

How to Protect



Install latest Microsoft patches. See
http://www.microsoft.com/technet/security/b
ulletin/MS00-78.asp
Install IIS lockdown tool if you want.
Don’t use IIS for critical functions, IMHO.
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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.
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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
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W2: ISAPI Extension Buffer
Overflows

Am I vulnerable?



SP2 installed? No, then you are.
Installed MS01-023, MS01-033, MS01044, 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
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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.
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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.
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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.
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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.
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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.
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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]
ITTIP Seminar
Copyright 2001 R.C.Marchany
72
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
ITTIP Seminar
Copyright 2001 R.C.Marchany
73
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.
ITTIP Seminar
Copyright 2001 R.C.Marchany
74
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
ITTIP Seminar
Copyright 2001 R.C.Marchany
75
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
ITTIP Seminar
Copyright 2001 R.C.Marchany
76
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
ITTIP Seminar
Copyright 2001 R.C.Marchany
77
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
ITTIP Seminar
Copyright 2001 R.C.Marchany
78
Common Vulnerable Ports

Small Services


Miscellaneous




Ports < 20/tcp/udp, Time: 37/tcp/udp
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.
ITTIP Seminar
Copyright 2001 R.C.Marchany
79
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.
ITTIP Seminar
Copyright 2001 R.C.Marchany
80