Sendmail is a Mail Transport Agent (MTA) used to send mail between machines.
A flaw in the handling of multi-part MIME messages was discovered in Sendmail. A remote attacker could create a carefully crafted message that could crash the sendmail process during delivery (CVE-2006-1173). By default on Red Hat Enterprise Linux, Sendmail is configured to only accept connections from the local host. Therefore, only users who have configured Sendmail to listen to remote hosts would be remotely vulnerable to this issue.
Users of Sendmail are advised to upgrade to these erratum packages, which contain a backported patch from the Sendmail team to correct this issue.