Cisco Router Forensics

Thomas Akin, CISSPDirector, Southeast Cybercrime Institute

Kennesaw State UniversityBlackHat Briefings, USA, 2002

Hacking Cisco

Cisco Bugtraq Vulnerabilities

• 1998 - 3• 1999 - 5• 2000 - 23• 2001 - 46• 2002 (est) - 94

Hacking Routers

Example Exploits:• HTTP Authentication Vulnerability

– using a URL of http://router.address/level/$NUMBER/exec/.... where $NUMBER is an integer between 16 and 99, it is possible for a remote user to gain full administrative access.

• NTP Vulnerability– By sending a crafted NTP control packet, it is possible to trigger a buffer overflow in the

NTP daemon

• SNMP Parsing Vulnerability– Malformed SNMP messages received by affected systems can cause various parsing and

processing functions to fail, which results in a system crash and reload. In some cases, access-list statements on the SNMP service do not protect the device

Hacking Routers

When a router is hacked it allows an attacker to

• DoS or disable the router & network…

• Compromise other routers…

• Bypass firewalls, IDS systems, etc…

• Monitor and record all outgoing an incoming traffic…

• Redirect whatever traffic they desire…

Cisco Routers in a Nutshell

Flash• Persistent• Holds

– Startup configuration

– IOS files

RAM• Non-Persistent• Holds

– Running configuration

– Dynamic tables (i.e)• Arp

• Routing

• NAT

• ACL violations

• Protocol Statistics

• Etc…

Router Forensics v/s Traditional Forensics

Traditional Forensics• Immediately shutdown

the system (or pull the power cord)

• Make a forensic duplicate

• Perform analysis on the duplicate

• Live system data is rarely recovered.

Router Forensics• Live system data is the

most valuable.• Immediate shutdown

destroys all of this data.• Persistent (flash) data

will likely be unchanged and useless.

• Investigators must recover live data for analysis

Computer Forensics: The Unholy Grail

The goal is to “catch the criminal behind the keyboard.” Not to find fascinating computer evidence.

Computer evidence is never the smoking gun. Most often computer evidence either

• Provides leads to other evidence…

• Corroborates other evidence…

Chain of Custody

Detailed, Methodical, Unquestionable….• Where you received the evidence…

• When you received the evidence…

• Who you received the evidence from…

• What your seizure methods were…

• Why you seized the evidence…

• How you maintained your chain of custody…

Example CoC Form

Example CoC Form

Incident Response

• DO NOT REBOOT THE ROUTER.

• Change nothing, record everything.

• Before you say it is an accident, make sure it isn’t an incident…

• Before you say it is an incident, make sure it isn’t an accident…

Accessing the Router

DO• Access the router

through the console• Record your entire

console session• Run show commands• Record the actual time

and the router’s time• Record the volatile

information

DON’T• REBOOT THE

ROUTER• Access the router

through the network• Run configuration

commands• Rely only on persistent

information

Recording Your Session

• Always start recording your session before you even log onto the router

• Frequently show the current time with the show clock detail command

Volatile EvidenceDirect Access

• show clock detail• show version• show running-config• show startup-config• show reload• show ip route• show ip arp• show users• show logging

• show ip interface• show interfaces• show tcp brief all• show ip sockets• show ip nat translations

verbose• show ip cache flow• show ip cef• show snmp user• show snmp group• show clock detail

Volatile Evidence Indirect Access

Remote evidence may be all you can get if the passwords have been changed…

• Port scan each router IPnmap -v -sS -P0 -p 1- Router.domain.comnmap -v -sU -P0 -p 1- Router.domain.comnmap -v -sR -P0 -p 1- Router.domain.com

• SNMP scan each router IPsnmpwalk –v1 Router.domain.com publicsnmpwalk –v1 Router.domain.com private

Intrusion Analysis

• IOS Vulnerabilities

• Running v/s Startup configurations

• Logging

• Timestamps

Logging

• Console LoggingThese will be captured by recording your session.

• Buffer LoggingIf buffered logging is turned on, the show logging command will show you the contents of the router log buffer, what level logging is performed at, and what hosts logging is sent to.

• Terminal LoggingThis allows non console sessions to view log messages.

• Syslog LoggingLog messages are sent to a syslog server when logging is turned on and the logging servername command is set.

Logging

• SNMP loggingIf SNMP is running, SNMP traps may be sent to a logging server.

• AAA LoggingIf AAA is running the check the aaa accounting commands to see what logging is being sent to the Network Access Server.

• ACL Violation LoggingACL can be configured to log any packets that match their rules by ending the ACL with the log or log-input keywords. These log messages are sent the the routers log buffer and to the syslog server.

Real Time Forensics

After removing or collecting information from your compromised router you can use the router to help monitor the network and itself by turning on logging if it wasn’t previously.

Router#config terminal

Router(config)#service timestamps log datatime msec \ localtime show-timezone

Router(config)#no logging console

Router(config)#logging on

Router(config)#logging buffered 32000

Router(config)#logging buffered informational

Router(config)#logging facility local6

Router(config)#logging trap informational

Router(config)#logging Syslog-server.domain.com

Real Time Forensics

Using AAA provided even greater ability to log information. TACACS+ even allows you to log every command executed on the router to your Network Access Server

Router#config terminal

Router(config)#aaa accounting exec default start-stop \ group tacacs+

Router(config)#aaa accounting system default stop-only \ group tacacs+

Router(config)#aaa accounting connection default \ start-stop group tacacs+

Router(config)#aaa accounting network default \ start-stop group tacacs+

Real Time Forensics

You can also use ACL logging to count packets and log specific events. By configuring syslog logging and analyzing your syslog files in real time you can perform real time monitoring

• The ACLaccess-list 149 permit tcp host 130.18.59.1 any eq \ 161 log-inputwill not block any packets, but will log all incoming SNMP requests from 130.18.59.1 to any internal host.

• The ACLsaccess-list 148 deny tcp 130.18.59.0 0.0.0.255 any \ eq 53 log-inputaccess-list 148 deny udp 130.18.59.0 0.0.0.255 any \ eq 53 log-inputwill block and log any DNS packets from the subnet 130.18.59.0/24 to any internal host.

Summary

• Hacking Cisco Routers• Router Hardware & Software• Router Forensics v/s Traditional Forensics• Computer Evidence & Chain of Custody• Incident Response• Accessing the Router• Gathering volatile evidence—internal & external• Gathering logging evidence• Performing Real Time Network Forensics

Thank you!

Thomas Akin

takin@kennesaw.edu

http://cybercrime.kennesaw.edu

On you conference CD you will find:

• A copy of this presentation

• A router forensics checklist

• A sample Chain of Custody form

• A sample Evidence Receipt tag