Public Vulnerability Reports

Exim host_aton() Buffer Overflow Vulnerability

01.07.05

BACKGROUND

Exim is a message transfer agent developed for use on Unix systems. More
information is available at:

 http://www.exim.org/

DESCRIPTION

Local exploitation of a buffer overflow vulnerability in Exim 4.41 may
allow execution of arbitrary commands with elevated privileges.

The problem specifically exists in the host_aton function. The function
fails to check the number of elements it stores in a fixed size array.
The elements come from a user-controlled string and are passed into the
program from a command line option.

ANALYSIS

Exploitation of this vulnerability will give an attacker access to the
mailer uid. The exim mailer is setuid root, but drops privileges before
the vulnerable code is reached. Having the mailer uid may allow access
to sensitive information in e-mail messages or possibly further
elevation.

DETECTION

Exim versions 4.40 and 4.41 have been confirmed vulnerable. The source
code for version 4.42 suggests that it is also vulnerable. It is
suspected that previous versions are vulnerable.

WORKAROUND

iDEFENSE is currently unaware of any effective workarounds for this
vulnerability.

VENDOR RESPONSE

The vulnerability has been fixed in Exim release 4.44.

CVE INFORMATION

The Common Vulnerabilities and Exposures (CVE) project has assigned the
names CAN-2005-0021 to these issues. This is a candidate for inclusion
in the CVE list (http://cve.mitre.org), which standardizes names for
security problems.

DISCLOSURE TIMELINE

12/23/2004   Initial vendor notification
12/29/2004   Initial vendor response
01/07/2005   Public disclosure

CREDIT

The discoverer of this vulnerability wishes to remain anonymous.

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LEGAL NOTICES

Copyright © 2004 Verisign, Inc.

Permission is granted for the redistribution of this alert
electronically. It may not be edited in any way without the express
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Disclaimer: The information in the advisory is believed to be accurate
at the time of publishing based on currently available information. Use
of the information constitutes acceptance for use in an AS IS condition.
There are no warranties with regard to this information. Neither the
author nor the publisher accepts any liability for any direct, indirect,
or consequential loss or damage arising from use of, or reliance on,
this information.