Clam AntiVirus is an open source (GPL) anti-virus toolkit for UNIX, designed especially for e-mail scanning on mail gateways.
Nikolaos Rangos discovered a vulnerability in ClamAV which exists because the recipient address extracted from email messages is not properly sanitized before being used in a call to "popen()" when executing sendmail (CVE-2007-4560). Also, NULL-pointer dereference errors exist within the "cli_scanrtf()" function in libclamav/rtf.c and Stefanos Stamatis discovered a NULL-pointer dereference vulnerability within the "cli_html_normalise()" function in libclamav/htmlnorm.c (CVE-2007-4510).
The unsanitized recipient address can be exploited to execute arbitrary code with the privileges of the clamav-milter process by sending an email with a specially crafted recipient address to the affected system. Also, the NULL-pointer dereference errors can be exploited to crash ClamAV. Successful exploitation of the latter vulnerability requires that clamav-milter is started with the "black hole" mode activated, which is not enabled by default.
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-0.91.2"