ClamAV is a GPL virus scanner.
Damian Put and an anonymous researcher reported a potential heap-based buffer overflow vulnerability in rebuildpe.c responsible for the rebuilding of an unpacked PE file, and a possible crash in chmunpack.c in the CHM unpacker.
By sending a malicious attachment to a mail server running ClamAV, or providing a malicious file to ClamAV through any other method, a remote attacker could cause a Denial of Service and potentially the execution of arbitrary code with the permissions of the user running ClamAV.
There is no known workaround at this time.
All ClamAV users should upgrade to the latest version:
# emerge --sync
# emerge --ask --oneshot --verbose ">=app-antivirus/clamav-0.88.5"