A new version of the Code Red worm is spreading on the Internet, more than 18 months after the original worm infected Web servers worldwide, according to alerts posted Wednesday by a number of antivirus software vendors.

The new version, labeled CodeRed.F, is almost identical to another Code Red variant, CodeRed.C, also known as Code Red II, according to information posted by F-Secure Corp. of Helsinki, Finland.

Code Red II first appeared about a month after the first worm, in August of 2001, and took advantage of the same Microsoft Corp. Internet Information Server (IIS) security flaw that the first Code Red worm exploited, but took the added step of installing a back door ("Trojan") program on the machines it infected, giving remote attackers total control of that system, F-Secure said.

Code Red worms use the IIS vulnerability to cause a buffer overflow on vulnerable Web servers. Once infected by Code Red, machines search for other vulnerable Web servers to infect.

The worm is programmed to spread for the first 19 days of each month, after which infected machines launch a day-long denial of service attack against the White House domain, www1.whitehouse.gov, then shut off, according to F-Secure.

Changes in just two bytes of code distinguish CodeRed.F from the Code Red II variant. Those changes disable a feature of Code Red II that caused it to become dormant at the end of 2002, according to an alert posted by Computer Associates International Inc.

As a result, the CodeRed.F will be able to continue spreading almost indefinitely, with serious repercussions for network administrators, Computer Associates said.

As of Wednesday, however, most antivirus vendors rated CodeRed.F a low risk, noting that it treads the well-worn trail of previous Code Red variants, exploiting an IIS vulnerability that many system administrators have long since patched.

In addition, because of its similarity to Code Red II, many antivirus software packages will detect the new variant without requiring a new virus definition, according to Computer Associates and Symantec Corp.

The systems most likely to be affected by the new worm are home systems that are not protected by antivirus or firewall software and "forgotten Web servers," many of which are already infected by earlier versions of Code Red, according to F-Secure.

Administrators who are running vulnerable versions of IIS were strongly encouraged to secure those systems using patches available from Microsoft's Web site. (See http://www.microsoft.com/technet/security/bulletin/MS01-033.asp or http://www.microsoft.com/technet/security/bulletin/MS01-044.asp.)

ITworld.com

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