Sendmail is a Mail Transport Agent (MTA) used to send mail between machines.
A flaw was found in the way sendmail handled NUL characters in the CommonName field of X.509 certificates. An attacker able to get a carefully-crafted certificate signed by a trusted Certificate Authority could trick sendmail into accepting it by mistake, allowing the attacker to perform a man-in-the-middle attack or bypass intended client certificate authentication. (CVE-2009-4565)
The CVE-2009-4565 issue only affected configurations using TLS with certificate verification and CommonName checking enabled, which is not a typical configuration.
This update also fixes the following bugs:
Previously, sendmail did not correctly handle mail messages that had a long first header line. A line with more than 2048 characters was split, causing the part of the line exceeding the limit, as well as all of the following mail headers, to be incorrectly handled as the message body. (BZ#499450)
When an SMTP-sender is sending mail data to sendmail, it may spool that data to a file in the mail queue. It was found that, if the SMTP-sender stopped sending data and a timeout occurred, the file may have been left stalled in the mail queue, instead of being deleted. This update may not correct this issue for every situation and configuration. Refer to the Solution section for further information. (BZ#434645)
Previously, the sendmail macro MAXHOSTNAMELEN used 64 characters as the limit for the hostname length. However, in some cases, it was used against an FQDN length, which has a maximum length of 255 characters. With this update, the MAXHOSTNAMELEN limit has been changed to 255. (BZ#485380)
All sendmail users should upgrade to these updated packages, which contain backported patches to correct these issues. After installing this update, sendmail will be restarted automatically.