Bofra worm sets trap for unwary

Zero day exploit used to produce zombies

A new family of worms which uses an unpatched vulnerability in Internet Explorer is spreading widely across the net.

Bofra-A poses as photos from an adult webcam in an attempt to fool users into clicking on a link. Clicking on the link causes the targeted PC to run malicious script hosted on a previously infected computer. This exploits the discovered IFRAME vulnerability in IE in an attempt to infect the target computer, as explained here.

Once a new system is infected, the worm sets up an embedded web server listening on a port between 1600/TCP and 1700/TCP. Infected PCs establish an IRC session on port 6667/TCP with a variety of public IRC servers, allowing hackers to control compromised machines. The worm also harvests to further its propagation. Unlike standard bulk-mailing worms, Bofra does not send copies of itself within infected email but a HTTP link that points to the host that sent the infected email.

Bofra-B uses the same techniques in an email which poses as an order confirmation from PayPal. Some anti-virus firms initially thought Bofra was a variant of the infamous MyDoom series. Further analysis suggests this classification is somewhat misleading. According to anti-virus firm F-Secure, there's only a 49 per cent correlation between the two groups of malware. Rival Sophos agrees.

"Detailed analysis of the Bofra worms reveals that the similarities they have with the MyDoom family of worms are outweighed by the differences," said Graham Cluley, senior technology consultant for Sophos. "For one thing, the Bofra worms spread between users in an entirely different way from the MyDoom worm which relied upon email attachments."

The vulnerability exploited by the worm affects all Windows versions of Internet Explorer, except those on Windows XP SP2 systems. More information on the exploit in available from US CERT here. As it promised last week, Microsoft yesterday issued a patch for its Microsoft Internet Security and Acceleration Server 2000 (ISA Server) and Microsoft Proxy Server 2.0 software, designed to fix an "important" security vulnerability. However the IFRAME vulnerability in IE exploited by Bofra remains outstanding. Anti-virus firm categorise the Bofra family of worms (AKA MyDoom-AG, MyDoom-AH or MyDoom-AI) as a medium to high risk. ®

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