Software Engineering Institute

The Portable Executable (PE) file format is a file format for executable files that is used in Microsoft Windows. PE files can be packed with executable packers, such as upack. The ClamAV anti-virus scanner can unpack and scan PE files that are packed with upack.

From ClamAV bug ID 878:
Secunia Research has discovered a vulnerability in ClamAV, which can be exploited by malicious people to compromise a vulnerable system.

The vulnerability is caused due to a boundary error within the "cli_scanpe()" function in libclamav/pe.c. This can be exploited to cause a heap-based buffer overflow via a specially crafted "Upack" executable.

Note that the ClamAV team has disabled the scanning of PE files that were packed with upack in older versions of ClamAV to prevent this vulnerability from being exploited.

A remote, unauthenticated attacker may be able to execute arbitrary code or cause ClamAV to crash.

Upgrade
Users are encouraged to upgrade to ClamAV .93, which was released to address this issue. Note that because of a workaround applied by the ClamAV team, ClamAV versions prior to .93 may not be able to scan PE files that were packed with the upack packer.

Do not run clamscan as root

To limit the impact of vulnerabilities in ClamAV, users and administrators should run clamscan with a limited user account.