Security Firm Caulks Sendmail Exploit

Security experts have found a flaw in Sendmail’s server software that will allow an attacker to hijack a server and view sensitive information.

Sendmail Mail Transfer Agent (MTA) is an SMTP server used on mail gateways to route and shuttle e-mail. It is offered as an open source Linux product and in commercial Unix versions: the new flaw affects both.

Internet Security Systems said today the Sendmail exploit is a signal race vulnerability caused by the mishandling of asynchronous signals.

By forcing the SMTP server to timeout at a specific instant, an attacker can run malicious code and: expose, delete, or modify programs and data on the system; and disrupt e-mail delivery.

Because Sendmail starts a new process for each connected server, attackers can exploit it on any machine connected to Sendmail.

Sendmail said it is not aware of any public exploit code for this vulnerability. has since plugged the hole in the latest open source version, 8.13.6, which may be accessed here. is also offering patches for 8.13.5 and 8.1211. is offering fixes for Unix system that may be affected here.

Sendmail has had its share of exploits pop up in the past.

In 2003, the Sendmail Consortium updated its popular open-source MTA to plug a security problem in header parsing. That flaw was also discovered by ISS.

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