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CERT Advisory CA-2003-25 Buffer Overflow in Sendmail

Original issue date: September 18, 2003
Last revised: --
Source: CERT/CC

A complete revision history is at the end of this file.

Systems Affected

* Systems running open-source sendmail versions prior to 8.12.10,
including UNIX and Linux systems

* Commercial releases of sendmail including Sendmail Switch,
Sendmail Advanced Message Server (SAMS), and Sendmail for NT

Overview

A vulnerability in sendmail could allow a remote attacker to execute
arbitrary code with the privileges of the sendmail daemon, typically
root.

I. Description

Sendmail is a widely deployed mail transfer agent (MTA). Many UNIX and
Linux systems provide a sendmail implementation that is enabled and
running by default. Sendmail contains a vulnerability in its address
parsing code. An error in the prescan() function could allow an
attacker to write past the end of a buffer, corrupting memory
structures. Depending on platform and operating system architecture,
the attacker may be able to execute arbitrary code with a specially
crafted email message.

This vulnerability is different than the one described in CA-2003-12.

The email attack vector is message-oriented as opposed to
connection-oriented. This 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 may 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 packet filters or firewalls.

Further information is available in VU#784980. Common Vulnerabilities
and Exposures (CVE) refers to this issue as CAN-2003-0694.

II. Impact

Depending on platform and operating system architecture, a remote
attacker could execute arbitrary code with the privileges of the
sendmail daemon. Unless the RunAsUser option is set, Sendmail
typically runs as root.

III. Solution

Upgrade or apply a patch

This vulnerability is resolved in Sendmail 8.12.10. Sendmail has also
released a patch that can be applied to Sendmail 8.9.x through 8.12.9.
Information about specific vendors is available in Appendix A. and in
the Systems Affected section of VU#784980.

Sendmail 8.12.10 is designed to correct malformed messages that are
transferred by the server. This should help protect other vulnerable
sendmail servers.

Enable the RunAsUser option

While there is no known complete workaround, consider setting the
RunAsUser option to reduce the impact of this vulnerability. It is
typically considered to be a good security practice to limit the
privileges of applications and services whenever possible.

Appendix A. Vendor Information

This appendix contains information provided by vendors. When vendors
report new information, this section is updated, and the changes are
noted in the revision history. If a vendor is not listed below, we
have not received their direct statement. Further vendor information
is available in the Systems Affected section of VU#784980.

Debian

The sendmail and sendmail-wide packages are vulnerable to this
issue. Updated packages are being prepared and will be available
soon.

F5 Networks

BIG-IP and 3-DNS products are not vulnerable.

IBM

The AIX Security Team is aware of the issues discussed in CERT
Vulnerability Note VU#784980.

The following APARs will be released to address this issue:

APAR number for AIX 4.3.3: IY48659 (available approx. 10/03/03)
APAR number for AIX 5.1.0: IY48658 (available approx. 10/15/03)
APAR number for AIX 5.2.0: IY48657 (available approx. 10/29/03)

An e-fix will be available shortly. The e-fix will be available
from:

ftp://ftp.software.ibm.com/aix/efixes/security/sendmail_4_efix.tar.Z

This vendor statement will be updated when the e-fix becomes
available.

Lotus

This is a sendmail-specific issue that does not affect any Lotus
products.

Network Appliance

NetApp products are not vulnerable to this problem.

NetBSD

NetBSD-current ships with sendmail 8.12.9 since June 1, 2003. The
patch was applied on September 17, 2003. In the near future we
would upgrade to sendmail 8.12.10.

Our official releases, such as NetBSD 1.6.1, are also affected
(they ship with older version of sendmail). They will be patched as
soon as possible. We would issue NetBSD Security Advisory on this
matter.

Openwall GNU/*/Linux

Openwall GNU/*/Linux is not vulnerable. We ship Postfix, not
Sendmail.

Red Hat

Red Hat Linux and Red Hat Enterprise Linux ship with a Sendmail
package vulnerable to these issues. Updated Sendmail packages are
available along with our advisory at the URLs below. Users of the
Red Hat Network can update their systems using the 'up2date' tool.

Red Hat Linux:

http://rhn.redhat.com/errata/RHSA-2003-283.html

Red Hat Enterprise Linux:

http://rhn.redhat.com/errata/RHSA-2003-284.html

The Sendmail Consortium

The Sendmail Consortium recommends that sites upgrade to 8.12.10
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/.

Sun

Sun acknowledges that our recent release of sendmail 8.12.10 is
affected by this issue on Solaris releases S7, S8 and S9.

A Sun Alert for this issue will be isuued very soon which will then
be available from:

http://sunsolve.Sun.COM/pub-cgi/retrieve.pl?doc=fsalert/56860

There are no patches available at this time. The Sun Alert will be
updated with the patch information as it becomes available. Please
refer to the Sun Alert when available, for more information.

SuSE

SuSE products shipping sendmail are affected. Update packages that
fix the vulnerability are being prepared and will be published
shortly.

Appendix B. References

* CERT/CC Vulnerability Note VU#784980 -
<http://www.kb.cert.org/vuls/id/784980>
* Michal Zalewski's post to BugTraq -
<http://www.securityfocus.com/archive/1/337839>
* Sendmail 8.12.10 - <http://www.sendmail.org/8.12.10.html>
* Sendmail patch for 8.12.9 -
<http://www.sendmail.org/patches/parse8.359.2.8>
* Sendmail 8.12.10 announcement -
<http://archives.neohapsis.com/archives/sendmail/2003-q3/0002.html
>
* Sendmail Secure Install -
<http://www.sendmail.org/secure-install.html>

_________________________________________________________________

This vulnerability was discovered by Michal Zalewski. Thanks to Claus
Assmann and Eric Allman of Sendmail for their help in preparing this
document.
_________________________________________________________________

Feedback can be directed to the author, Art Manion.
______________________________________________________________________

This document is available from:
http://www.cert.org/advisories/CA-2003-25.html
______________________________________________________________________

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
U.S.A.

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

http://www.cert.org/CERT_PGP.key

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

Getting security information

CERT publications and other security information are available from
our web site

http://www.cert.org/

To subscribe to the CERT mailing list for advisories and bulletins,
send email to majordomo@cert.org. Please include in the body of your
message

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* "CERT" and "CERT Coordination Center" are registered in the U.S.
Patent and Trademark Office.
______________________________________________________________________

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______________________________________________________________________

Conditions for use, disclaimers, and sponsorship information

Copyright 2003 Carnegie Mellon University.

Revision History

September 18, 2003: Initial release

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