Exim string_format() buffer overflow

ID VU:682457
Type cert
Reporter CERT
Modified 2010-12-13T00:00:00



The Exim mail server contains a buffer overflow that could allow a remote attacker to execute arbitrary code on an affected system.


Exim is a message transfer agent (MTA) developed at the University of Cambridge for use on Unix systems connected to the Internet. The internal string handling functions of the Exim software contain a function called string_format(). The version of this function included with Exim versions prior to 4.70 contains a flaw that can result in a buffer overflow. An attacker can exploit this vulnerability by crafting message headers that are subsequently supplied to Exim logging functions.

Note: this vulnerability has been reported being exploited in the wild.


A remote, unauthenticated attacker may be able to execute arbitrary code with the privileges of the Exim server. A separate vulnerability in Exim could then allow the attacker to escalate privileges to root.


Apply an update

Users who obtain Exim from a third-party vendor, such as their operating system vendor, should see the vendor information portion of this document for a partial list of affected vendors.

This vulnerability is reportedly addressed in Exim version 4.70. Users of Exim from the original source distribution should upgrade to this version or later, as appropriate. Users who are unable to upgrade are encouraged to apply the following patch from the Exim developers:

Vendor Information

Vendor| Status| Date Notified| Date Updated
Debian GNU/Linux| | -| 10 Dec 2010
SUSE Linux| | -| 13 Dec 2010
Ubuntu| | -| 13 Dec 2010
If you are a vendor and your product is affected, let us know.

CVSS Metrics

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


  • <http://www.exim.org/lurker/message/20101207.215955.bb32d4f2.en.html>
  • <http://www.exim.org/lurker/message/20101210.164935.385e04d0.en.html>
  • <http://bugs.exim.org/show_bug.cgi?id=787>
  • <http://git.exim.org/exim.git/commitdiff/24c929a2>
  • <http://lists.exim.org/lurker/message/20101209.172233.abcba158.en.html>
  • <https://bugzilla.redhat.com/show_bug.cgi?id=661756>


This vulnerability was discovered as a result of its exploitation in the wild. Sergey Kononenko provided confirmation and public analysis.

This document was written by Chad R Dougherty.

Other Information

  • CVE IDs: CVE-2010-4344
  • Date Public: 07 Dec 2010
  • Date First Published: 13 Dec 2010
  • Date Last Updated: 13 Dec 2010
  • Severity Metric: 19.77
  • Document Revision: 8