Netsky.P Spreads Through Ancient Security Hole

A new variant of the worm utilizes an Internet Explorer bug patched almost three years ago.

McAfees Avert labs is reporting that a new variant of the Netsky worm, Netsky.P, is spreading quickly. Both McAfee and Trend Micro Inc. rate Netsky.P as a "medium" threat and Symantec Corp. has rated it a "2" (for "Low," on a scale of 1 to 5). This is the first new variant of Netsky seen in about a week, a long hiatus for recent times.

This new variant is very much like other Netsky versions with two differences, according to Vincent Gullotto, vice president of the McAfee Avert Virus and Vulnerability Emergency Response Team. The initial seeding of the worm, referring to the initial group of users to whom the virus author distributed it, appears to have been in Australia. Its not clear whether or how this would facilitate spreading of the worm, but it is unusual.

The other interesting and unusual characteristic of this worm is that is utilizes a very old vulnerability in Internet Explorer, the Incorrect MIME Header (MS01-020) bug. This bug, patched almost three years ago, allowed a hostile HTML e-mail to execute arbitrary code if viewed in the preview pane of a mail client.

Once very much in vogue among virus writers, it has fallen into disuse in recent times. Its not possible to know if Netsky.P is spreading because of the MS01-020, but Gullotto said it is probably a "contributing factor."

Like other Netsky variants, this one spreads mainly through a built-in SMTP engine to e-mail addresses harvested out of the users files. It varies the subject line and body of the message, and the from: address will also be randomly selected from addresses harvested from the user. The attachment uses a variety of executable and .ZIP file names.

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