Virus smuggling risk for Outlook Express users

MS bug foils Mail filtering utilities

Security researchers have identified a way to smuggle virus laden emails past AV checkers and into the in-boxes of Outlook Express users.

A demo suggests it's possible to send attachments to Outlook Express users using non-standard attachment techniques, by encapsulating the data in Carriage Return (<CR>) specifiers in the subject line of an email.

Mail filtering utilities usually don't search the subject line for this type of data, so a maliciously constructed email might appear as an attachment to Outlook Express users. Users of other email clients, such as Eudora, wouldn't see the attachment, so the risk is restricted to Outlook Express 5.5. and 6.0 users on Windows PCs.

Security researcher Valentijn Sessink, who discovered the bug, has yet to hear back from Microsoft on the issue, but suspects Outlook users may also be affected, although he hasn't tested this. Outlook Express on Macintosh seems unaffected, tests suggest.

Jack Clark, product marketing manager of the McAfee division of Network Associates, agreed that the email scanning components of AV tools don't normally scan subject lines. News of the vulnerability may spur
change, he said.

However he said that PC users with AV software should still be protected from viruses even if they get into their Inboxes.

"If malicious code sent in this way is executed we'll still pick it up, it's just that it won't be picked up as early," he told us. ®

External links:
Outlook Express attachment carriage return/linefeed encapsulation filtering bypass vulnerability

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