A serious flaw in Sendmail creates a way for attackers to take over email servers, security tools firm ISS warned yesterday.

Sendmail has a buffer overflow vulnerability, enabling attacks (using maliciously-constructed emails) of servers. Sendmail technology is the transport mechanism for most of the Net's email traffic.

ISS warns: "Vulnerable Sendmail servers will not be protected by legacy security devices such as firewalls and/or packet filters. This vulnerability is especially dangerous because the exploit can be delivered within an email message and the attacker doesn't need any specific knowledge of the target to launch a successful attack."

Sendmail versions from 5.79 to 8.12.7 are vulnerable.

According to security clearing house CERT, an exploit based on the vulnerability is yet to used by black hats. But that's no reason for complaceny - the flaw is serious and Sendmail is too tempting a target.

Sendmail Corporation advises sites upgrade to 8.12.8 if possible. Many vendors include vulnerable Sendmail servers as part of their software distributions, hence the need to patch Unix and Linux systems as well as dedicated mail servers. CERT's advisory provides links to available patches, which are mostly already available. ®

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