CERT Advisory CA-2003-12 Buffer Overflow in Sendmail

From: CERT Advisory (cert-advisory@cert.org)
Date: 03/29/03

Date: Sat, 29 Mar 2003 14:56:26 -0500
From: CERT Advisory <cert-advisory@cert.org>
To: cert-advisory@cert.org


CERT Advisory CA-2003-12 Buffer Overflow in Sendmail

   Original release date: March 29, 2003
   Last revised:
   Source: CERT/CC

   A complete revision history can be found at the end of this file.

Systems Affected

     * Sendmail Pro (all versions)
     * Sendmail Switch 2.1 prior to 2.1.6
     * Sendmail Switch 2.2 prior to 2.2.6
     * Sendmail Switch 3.0 prior to 3.0.4
     * Sendmail for NT 2.X prior to 2.6.3
     * Sendmail for NT 3.0 prior to 3.0.4
     * Systems running open-source sendmail versions prior to 8.12.9,
       including UNIX and Linux systems


   There is a vulnerability in sendmail that can be exploited to cause a
   denial-of-service condition and could allow a remote attacker to
   execute arbitrary code with the privileges of the sendmail daemon,
   typically root.

I. Description

   There is a remotely exploitable vulnerability in sendmail that could
   allow an attacker to gain control of a vulnerable sendmail server.
   Address parsing code in sendmail does not adequately check the length
   of email addresses. An email message with a specially crafted address
   could trigger a stack overflow. This vulnerability was discovered by
   Michal Zalewski.

   This vulnerability is different than the one described in CA-2003-07.

   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.

   This vulnerability has been successfully exploited to cause a
   denial-of-service condition in a laboratory environment. It is
   possible that this vulnerability could be used to execute code on some
   vulnerable systems.

   The CERT/CC is tracking this issue as VU#897604. This reference number
   corresponds to CVE candidate CAN-2003-0161.

   For more information, please see


   For the latest information about this vulnerability, including the
   most recent vendor information, please see


   This vulnerability is distinct from VU#398025.

II. Impact

   Successful exploitation of this vulnerability may cause a
   denial-of-service condition or 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 by the contents of a malicious
   email message.

III. Solution

Apply a patch from Sendmail, Inc.

   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 8.12.9. These patches, and a signature file,
   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 the statements they provided in Appendix A of this
   advisory. The most recent vendor information can be found in the
   systems affected section of VU#897604.

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.

Appendix A. - Vendor Information

   This appendix contains information provided by vendors for this
   advisory. As vendors report new information to the CERT/CC, we will
   update this section and note the changes in our revision history. If a
   particular vendor is not listed below, we have not received their

Red Hat Inc.

   Red Hat distributes sendmail in all Red Hat Linux distributions. We
   are currently [Mar29] working on producing errata packages to correct
   this issue, when complete these will be available along with our
   advisory at the URL below. At the same time users of the Red Hat
   Network will be able to update their systems using the 'up2date' tool.

   Red Hat Linux:


   Red Hat Enterprise Linux:


The Sendmail Consortium

   The Sendmail Consortium recommends that sites upgrade to 8.12.9
   whenever possible. Alternatively, patches are available for 8.9, 8.10,
   8.11, and 8.12 on http://www.sendmail.org/.

Sendmail, Inc.

   All commercial releases including Sendmail Switch, Sendmail Advanced
   Message Server (which includes the Sendmail Switch MTA), Sendmail for
   NT, and Sendmail Pro are affected by this issue. Patch information is
   available at http://www.sendmail.com/security/.

   Our thanks to Eric Allman, Claus Assmann, Greg Shapiro, and Dave
   Anderson of Sendmail for reporting this problem and for their
   assistance in coordinating the response to this problem. We also thank
   Michal Zalewski for discovering this vulnerability.

   Authors: Art Manion and Shawn V. Hernan

   This document is available from:

CERT/CC Contact Information

   Email: cert@cert.org
          Phone: +1 412-268-7090 (24-hour hotline)
          Fax: +1 412-268-6989
          Postal address:
          CERT Coordination Center
          Software Engineering Institute
          Carnegie Mellon University
          Pittsburgh PA 15213-3890

   CERT/CC personnel answer the hotline 08:00-17:00 EST(GMT-5) /
   EDT(GMT-4) Monday through Friday; they are on call for emergencies
   during other hours, on U.S. holidays, and on weekends.

Using encryption

   We strongly urge you to encrypt sensitive information sent by email.
   Our public PGP key is available from

   If you prefer to use DES, please call the CERT hotline for more

Getting security information

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   Revision History

   March 29,2003: Initial release

Version: PGP 6.5.8