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Code Red Worm exploits buffer overflow
CERT Incident Note IN-2001-08: "Code Red" Worm Exploiting Buffer Overflow In IIS Indexing Service DLL

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

Release Date: July 19, 2001

Systems Affected


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.


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

Additional detailed analysis of this worm has been published by eEye Digital Security at http://www.eeye.com.


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:


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.


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


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.

Author(s): Allen Householder

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