Software Engineering Institute

The Symantec AntiVirus Library is used in many Symantec and third-party virus scanning products, including Symantec Norton Antivirus and Symantec BrightMail AntiSpam.

The AntiVirus Library DEC2EXE component contains a flaw in virtual file offset checking that can result in a heap overflow condition and the ability for an attacker to execute arbitrary code contained within the UPX file being scanned. Before the UPX file is uncompressed, the Portable Executable (PE) header is reconstructed. If a negative file offset to a crafted PE header is specified, and this crafted header contains malicious information, subsequent bounds calculations involving data from the legitimate PE header will result in a heap overflow.

A remote unauthenticated attacker is able to execute arbitrary code with no restrictions on content. This may not require manual intervention if the malicious file is sent to and automatically scanned by a client or server (such as an electronic mail gateway) that uses the Symantec AntiVirus Library.

Apply an update
Updates for Symantec products are provided through the LiveUpdate functionality of the product or from the Symantec Product Support web page.

In the meantime, Symantec Security Response Bulletin SYM05-003 provides a number of workarounds to disable or remove the DEC2EXE module.