According to rival Internet Security Systems' X-Force research group, which discovered the flaw, the bug is in the DEC2EXE module of the Symantec Antivirus Library, a part of the scanning engine that's able to peek into compressed executable files squeezed with the UPX (Ultimate Packer for eXecutables) format.
"This vulnerability can be triggered by an unauthenticated remote attacker, without user interaction, by sending an e-mail containing a crafted UPX file to the target Symantec AntiVirus Library on client, server, and gateway implementations," said X-Force in its advisory. A successful attack could give the attacker complete control of the supposedly-protected system.
Symantec ranked the danger as "High," while Danish security firm Secunia, which also posted a warning, rated it as "Highly Critical."
Symantec posted a security alert on its Web site that listed the 29 vulnerable Windows (and Macintosh) products, along with recommendations to update and/or upgrade the flawed software.
The Cupertino, Calif.-based security giant spun the news by claiming that even before ISS notified it of the vulnerability, it had already removed the DEC2EXE module from the scan engine upgrades in most of its products. It now plans to strip the offending module from all affected versions during upcoming maintenance releases.
Even though a rival dug up the bug, there didn't seem to be any ill feelings on Symantec's part. "Symantec appreciates the actions of the X-Force research team and X-Force's Alex Wheeler in particular for identifying this issue to Symantec and their cooperation and coordination while Symantec worked to resolve all issues," the company said in a statement.