Vulnerability Note VU#398025

Remote Buffer Overflow in Sendmail

Original Release date: 03 Mar 2003 | Last revised: 15 Sep 2003

Overview

There is a vulnerability in sendmail that may allow remote attackers to gain the privileges of the sendmail daemon, typically root.

Description

Researchers at Internet Security Systems (ISS) have discovered a remotely exploitable vulnerability in sendmail. This vulnerability could allow an intruder to gain control of a vulnerable sendmail server.

Most organizations have a variety of mail transfer agents (MTAs) at various locations within their network, with at least one exposed to the Internet. Since sendmail is the most popular MTA, most medium-sized to large organizations are likely to have at least one vulnerable sendmail server. In addition, many UNIX and Linux workstations provide a sendmail implementation that is enabled and running by default.

This vulnerability is message-oriented as opposed to connection-oriented. That means that the vulnerability is triggered by the contents of a specially-crafted email message rather than by lower-level network traffic. This is important because an MTA that does not contain the vulnerability will pass the malicious message along to other MTAs that may be protected at the network level. In other words, vulnerable sendmail servers on the interior of a network are still at risk, even if the site's border MTA uses software other than sendmail. Also, messages capable of exploiting this vulnerability may pass undetected through many common packet filters or firewalls.

Sendmail has indicated to the CERT/CC that this vulnerability has been successfully exploited in a laboratory environment. We do not believe that this exploit is available to the public. However, this vulnerability is likely to draw significant attention from the intruder community, so the probability of a public exploit is high.

A successful attack against an unpatched sendmail system will not leave any messages in the system log. However, on a patched system, an attempt to exploit this vulnerability will leave the following log message:

    Dropped invalid comments from header address

Although this does not represent conclusive evidence of an attack, it may be useful as an indicator.

A patched sendmail server will drop invalid headers, thus preventing downstream servers from receiving them.

Impact

Successful exploitation of this vulnerability may allow an attacker to gain the privileges of the sendmail daemon, typically root. Even vulnerable sendmail servers on the interior of a given network may be at risk since the vulnerability is triggered from the contents of a malicious email message.

Solution

Apply a patch from Sendmail

Sendmail has produced patches for versions 8.9, 8.10, 8.11, and 8.12. However, the vulnerability also exists in earlier versions of the code; therefore, site administrators using an earlier version are encouraged to upgrade to 8.12.8. These patches are located at

Apply a patch from your vendor

Many vendors include vulnerable sendmail servers as part of their software distributions. We have notified vendors of this vulnerability and recorded their responses in the systems affected section of this document.

Enable the RunAsUser option

There is no known workaround for this vulnerability. Until a patch can be applied, you may wish to set the RunAsUser option to reduce the impact of this vulnerability. As a good general practice, the CERT/CC recommends limiting the privileges of an application or service whenever possible.

Systems Affected (Learn More)

VendorStatusDate NotifiedDate Updated
Apple Computer Inc.Affected21 Feb 200303 Mar 2003
BSD/OSAffected26 Feb 200303 Mar 2003
ConectivaAffected26 Feb 200304 Mar 2003
DebianAffected26 Feb 200304 Mar 2003
FreeBSDAffected13 Jan 200303 Mar 2003
Gentoo LinuxAffected04 Mar 200304 Mar 2003
Hewlett-Packard CompanyAffected27 Jan 200315 Sep 2003
IBMAffected28 Jan 200313 Mar 2003
MandrakeSoftAffected26 Feb 200304 Mar 2003
NetBSDAffected26 Feb 200304 Mar 2003
Nortel NetworksAffected26 Feb 200322 Apr 2003
OpenBSDAffected03 Mar 200303 Mar 2003
OpenPKGAffected04 Mar 200304 Mar 2003
Red Hat Inc.Affected19 Feb 200303 Mar 2003
Sendmail Inc.Affected13 Jan 200303 Mar 2003
If you are a vendor and your product is affected, let us know.View More »

CVSS Metrics (Learn More)

Group Score Vector
Base N/A N/A
Temporal N/A N/A
Environmental N/A N/A

References

Credit

Our thanks to Internet Security Systems, Inc. for discovering this problem, and to Eric Allman, Claus Assmann, and Greg Shapiro of Sendmail for notifying us of this problem. We thank both groups for their assistance in coordinating the response to this problem.

This document was written by Jeffrey P. Lanza and Shawn V. Hernan.

Other Information

  • CVE IDs: CAN-2002-1337
  • CERT Advisory: CA-2003-07
  • Date Public: 03 Mar 2003
  • Date First Published: 03 Mar 2003
  • Date Last Updated: 15 Sep 2003
  • Severity Metric: 66.00
  • Document Revision: 24

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