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[ISN] Sendmail flaw puts systems at risk, again


By Joris Evers
IDG News Service

Systems running sendmail are at risk of hacker attacks because of a
flaw in the way the commonly used e-mail server software handles long
e-mail addresses, experts warned Saturday. This is the second serious
bug announced this month, which is causing some sendmail users to look
for alternatives.

Sendmail does not adequately check the length of e-mail addresses. An
e-mail message with a specially crafted address can trigger a stack
overflow, potentially allowing an attacker to gain control of a
vulnerable sendmail server, the CERT Coordination Center warned in an
advisory Saturday.

Sendmail servers that aren't directly connected to the Internet are
also at risk, since the vulnerability is triggered by the contents of
a malicious e-mail message that can be handed on from server to
server, CERT said.

Many vendors distribute vulnerable versions of sendmail and users
should check with their vendors for a security patch, CERT said.  
Sendmail is the most commonly used mail transfer agent (MTA) and
handles the majority of all Internet e-mail traffic.

Sendmail and the Sendmail Consortium urge users of their versions to
upgrade to sendmail 8.12.9 or apply a patch, they said in a joint
advisory Saturday. The Sendmail Consortium develops an open source
version of sendmail that is distributed with free and commercial
operating systems. Sendmail sells a commercial product based on the
open source sendmail software.

The problem affects all versions of Sendmail Pro, all versions of open
source sendmail prior to 8.12.9, and several versions of Sendmail
Switch and Sendmail for NT, according to CERT.

The e-mail address parser flaw is the second "critical" bug in
sendmail announced and patched this month. The earlier vulnerability
occurred because of an error in a function that checks whether
addresses in the e-mail message header are valid. This could also
allow an attacker to take over a sendmail server, experts said.

Some users have had it with sendmail, according to postings on the
topic on "News for nerds" Web site Slashdot.org.

"This is the straw that breaks the camel's back. I'm changing to
another MTA," writes one user. "Sendmail: The IIS of Open Source,"  
writes another, referring to Microsoft's Internet Information Server
Web server software, which has had its share of security issues.

However, other forum postings criticize qmail and Postfix, two
sendmail alternatives, and point out that this latest sendmail flaw is
likely difficult to exploit.

CERT said it successfully exploited the flaw to knock the sendmail
server offline and that it is possible to execute code on some systems
by exploiting this flaw.

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