ClamAV is a GPL virus scanner.
Zero Day Initiative (ZDI) reported a heap buffer overflow vulnerability. The vulnerability is due to an incorrect boundary check of the user-supplied data prior to copying it to an insufficiently sized memory buffer. The flaw occurs when the application attempts to handle compressed UPX files.
For example by sending a maliciously crafted UPX file into a mail server that is integrated with ClamAV, a remote attacker's supplied code could be executed with escalated privileges.
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"