Sendmail is a widely used Mail Transport Agent (MTA) which is included in all Red Hat Enterprise Linux distributions.
During a code audit of Sendmail by ISS, a critical vulnerability was uncovered that affects unpatched versions of Sendmail prior to version 8.12.8. A remote attacker can send a carefully crafted email message which, when processed by sendmail, causes arbitrary code to be executed as root.
We are advised that a proof-of-concept exploit is known to exist, but is not believed to be in the wild.
Since this is a message-based vulnerability, MTAs other than Sendmail may pass on the carefully crafted message. This means that unpatched versions of Sendmail inside a network could still be at risk even if they do not accept external connections directly.
All users are advised to update to these erratum packages which contain a backported patch to correct this vulnerability.
Red Hat would like to thank Eric Allman for his assistance with this vulnerability.