ClamAV is a GPL virus scanner.
Hendrik Weimer discovered that ClamAV fails to properly handle deeply nested MIME multipart/mixed content.
By sending a specially crafted email with deeply nested MIME multipart/mixed content an attacker could cause ClamAV to crash.
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-0.88.7"