ClamAV is a GPL virus scanner.
Damian Put has discovered a boundary error in the pefromupx() function used by the UPX extraction module, which unpacks PE Windows executable files. Both the "clamscan" command-line utility and the "clamd" daemon are affected.
By sending a malicious attachment to a mail server running ClamAV, a remote attacker can 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-0.88.4"