// back

Exim dns_buld_reverse() Buffer Overflow Vulnerability



Exim is a mail transfer agent (MTA) for Unix systems similar to
sendmail. More information is available at the following URL:



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 dns_build_reverse() function. The
function fails to check the length of a string which it copies into a
fixed length buffer. This string is user controlled and passed into the
program from a command line option.

The following example demonstrates an input that will crash Exim:

/path/to/exim-binary -bh ::%A:::::::::::::::::`perl -e 'print pack("L",0xdeadbeef) x 256'`


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 email messages, or possibly further


iDEFENSE has confirmed the existence of this vulnerability in Exim
versions 4.40 and 4.41. A source audit of version 4.42 suggests that it
is also vulnerable. It is suspected that earlier versions are also


iDEFENSE is currently unaware of any effective workarounds for this


The vulnerability has been fixed in Exim release 4.44.


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.


09/30/2004   Initial vendor notification
09/30/2004   Initial vendor response
01/14/2005   Public disclosure


The discoverer of this vulnerability wishes to remain anonymous.

Get paid for vulnerability research


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
written consent of iDEFENSE. If you wish to reprint the whole or any
part of this alert in any other medium other than electronically, please
email customerservice@idefense.com for permission.

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.