CERT^® Incident Note IN-2001-08

"Code Red" Worm Exploiting Buffer Overflow In IIS Indexing Service DLL

The CERT/CC has received reports of new self-propagating malicious code exploiting the vulnerability described in CERT Advisory CA-2001-13 Buffer Overflow In IIS Indexing Service DLL. These reports indicate that the "Code Red" worm has already affected more than 13,000 hosts.

Description

In examples we have seen, the "Code Red" worm attack sequence proceeds as follows:

• The victim host is scanned for TCP port 80.
• The attacking host sends the exploit string to the victim.
• The worm, now executing on the victim host, checks for the existence of c:\notworm. If found, the worm ceases execution.
• If c:\notworm is not found, the worm begins spawning threads to scan random IP addresses for hosts listening on TCP port 80, exploiting any vulnerable hosts it finds.
• If the victim host's default language is English, then after 100 scanning threads have started and a certain period of time has elapsed following infection, all web pages served by the victim host are defaced with the message,

HELLO! Welcome to http://www.worm.com! Hacked By Chinese!

• If the victim host's default language is not English, the worm will continue scanning but no defacement will occur.

Impact

In addition to web site defacement, affected systems may experience performance degradation as a result of this worm.

Each instance of the "Code Red" worm uses the same random number generator seed to create the list of IP addresses it scans. Therefore, each victim host begins scanning the same IP addresses that previous instances have scanned, which could result in a denial of service against the IP addresses earliest in the list.

Furthermore, it is important to note that while the "Code Red" worm appears to merely deface web pages on affected systems and attack other systems, the IIS indexing vulnerability it exploits can be used to execute arbitrary code in the Local System security context, effectively giving an attacker complete control of the victim system. It is therefore imperative to apply the remedies described in the Solutions section of this document.

System Footprint

The "Code Red" worm can be identified on victim machines by the presence of the following string in IIS log files:

/default.ida?NNNNNNNNNNNNNNNNNNNNNNNNNNNNNNNNNNNNNNNNNNNNNNNNNNNNNNNNN
NNNNNNNNNNNNNNNNNNNNNNNNNNNNNNNNNNNNNNNNNNNNNNNNNNNNNNNNNNNNNNNNNNNNNN
NNNNNNNNNNNNNNNNNNNNNNNNNNNNNNNNNNNNNNNNNNNNNNNNNNNNNNNNNNNNNNNNNNNNNN
NNNNNNNNNNNNNNNNNNNNNNNNNNN%u9090%u6858%ucbd3%u7801%u9090%u6858%ucbd3%
u7801%u9090%u6858%ucbd3%u7801%u9090%u9090%u8190%u00c3%u0003%u8b00%u531
b%u53ff%u0078%u0000%u00=a 

Additionally, web pages on victim machines may be defaced with the following message:

HELLO! Welcome to http://www.worm.com! Hacked By Chinese!

Network Footprint

A host running an active instance of the "Code Red" worm will scan random IP addresses on port 80/TCP looking for other hosts to infect.

Solutions

The CERT/CC encourages all Internet sites to review CERT Advisory CA-2001-13 and ensure workarounds or patches have been applied on all affected hosts on your network.

If you believe a host under your control has been compromised, you may wish to refer to

Steps for Recovering from a UNIX or NT System Compromise

Reporting

The CERT/CC is interested in receiving reports of this activity. If machines under your administrative control are compromised, please send mail to cert@cert.org.

CERT/CC Contact Information

Email: cert@cert.org
Phone: +1 412-268-7090 (24-hour hotline)
Fax: +1 412-268-6989
Postal address:

CERT Coordination Center
Software Engineering Institute
Carnegie Mellon University
Pittsburgh PA 15213-3890
U.S.A.

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Copyright 2001 Carnegie Mellon University.

Revision History

July 19, 2001: Initial Release
January 17, 2002: Updated Reporting section