Sendmail flaw puts systems at risk, again

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 serious bug, the second affecting sendmail announced this month, has some users looking for alternatives.
Sendmail doesn't 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.
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 and handles the majority of Internet e-mail traffic.
Sendmail Inc. 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. The Sendmail Consortium develops an open-source version of sendmail that's distributed with both free and commercial operating systems. Sendmail Inc. 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.
CERT said that it successfully exploited the flaw to knock a sendmail server off-line and that it's possible to execute code on some systems by exploiting this flaw.
The e-mail address parser flaw is the second "critical" bug in sendmail announced and patched this month (see story). 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.

Reprinted with permission from

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