A vulnerability has been discovered in the Domain Name System (DNS) Server Service in Microsoft Windows 2000 and 2003 operating systems. The Microsoft DNS service Remote Procedure Call (RPC) implementation contains a stack buffer overflow. This vulnerability may allow a remote attacker to execute arbitrary code with SYSTEM privileges.
This vulnerability has already been exploited in several attacks. Cisco® has obtained exploit files, and has confirmed that the Cisco Security Agent is effective in stopping these exploits, using the default security policy configuration. Current supported versions of Cisco Security Agent 4.5.x, 5.0.x, 5.1.x, and 5.2.x are all effective in stopping the exploits seen to date.
Details of the Vulnerability
Details of the vulnerability are documented by Microsoft1 and by the Computer Emergency Response Team (CERT)2:
A stack-based buffer overflow vulnerability in the RPC interface in the Domain Name System (DNS) Server Service in Microsoft Windows 2000 and 2003 operating systems allows remote attackers to execute arbitrary code, by sending a specially crafted RPC packet to the RPC management interface of an affected system.
RPC is a protocol that a program can use to request a service from a program located on another computer in a network. RPC helps with interoperability because the program using RPC does not have to understand the network protocols that are supporting communication. In RPC, the requesting program is the client and the service-providing program is the server.
How Cisco Security Agent Stops the Exploit
Cisco Security Agent default policies contain multiple rules that stop the exploit from doing any damage. No changes to the Cisco Security Agent binaries or default configuration are required to get this protection.
The following actions have been observed being blocked by Cisco Security Agent running the default security policies:
• The receipt of a TCP connection from a remote IP address
• Execution of a system function from a buffer, through a buffer overflow
• The attacked service attempted to execute a command shell (CMD.EXE)
This testing is shown in Figure 1.
Figure 1. Cisco Security Agent Default Configuration Stops the MS DNS 0-Day Exploit (Tested on Cisco Security Agent 5.2)
Note: The exploit was tested at Cisco, with the agent in Test mode, which will cause the agent to alert (but not block) malicious behavior. This was done to observe all possible ways that the Cisco Security Agent default policies would stop the exploit. When the agent is in Protect mode (the typical operational configuration), the first rule would kill the exploit: no subsequent events would be seen, since the exploit would be terminated before it could perform any malicious actions.
Testing was performed against the Cisco Security Agent default policies. No binary or policy update was needed for Cisco Security Agents to be effective. In short, this was a true test of "day-zero" protection. This is similar to what Cisco has seen with earlier exploits and worms-the default Cisco Security Agent configuration stopped the exploit, with no binary or policy updates required. The following is a partial list of prior worms and exploits that Cisco Security Agent has stopped via the default security policy settings:
Exploits
Worms
Exploits
Worms
ANI 0Day
OS vulnerability
MS06-035
OS vulnerability
Bagle
E-mail worm
MS06-040
OS vulnerability
BigYellow
Network worm
MS06-070
OS vulnerability
Blackworm
Network worm
MS07-014
Application vulnerabilities
Blaster
Network worm
Excel hlink dll
Application vulnerability
Bugbear
E-mail worm
MS RDS ActiveX
OS vulnerability
Code Red
Network worm
MS XML Core Svs
OS vulnerability
Debploit
Network worm
Nimda
Network worm
Fizzer
E-mail worm
Pentagone/Gonner
E-mail worm
Gator/Gain
Spyware
Sasser
Network worm
Hotbar
Spyware
Sircam
E-mail worm
HTTP Dir Traversal
Web server vulnerability
Sobig
E-mail worm
IE Text Range
Application vulnerability
Storm Trojan
E-mail worm
IE VML BO
Application vulnerability
WMF 0day
OS vulnerability
SQL Slammer
Network worm
Word BO
Application vulnerability
SQL Snake
Network worm
W32.Rinbot.H
Network worm
JPEG/GDI+
Malware downloader
Zotob
Network worm
MyDoom
E-mail worm
This exploit is only the latest example of new and mutating attacks that can seriously affect an organization's computing and network environments. The key to stopping these new attacks is two-fold: the ability to stop the attack without requiring any changes to the default configuration, and multiple rules in the default policies that provide defense in depth.
