Exim dns_buld_reverse() Buffer Overflow Vulnerability
iDEFENSE Security Advisory 01.14.05
www.idefense.com/application/poi/display?id=183&type=vulnerabilities
January 14, 2005
I. BACKGROUND
Exim is a mail transfer agent (MTA) for Unix systems similar to
sendmail. More information is available at the following URL:
http://www.exim.org/
II. 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 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:
/usr/bin/exim -bh ::%A`perl -e 'print pack('L',0xdeadbeef') x 256'`
III. 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 email messages, or possibly further
elevation.
IV. DETECTION
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
vulnerable.
V. WORKAROUND
iDEFENSE is currently unaware of any effective workarounds for this
vulnerability.
VI. VENDOR RESPONSE
A patch for Exim release 4.43 which addresses this vulnerability is
available at:
http://www.exim.org/mail-archives/exim-announce/2005/msg00000.html
The patch will be incorporated into a future Exim release (4.50).
VII. CVE INFORMATION
A Mitre Corp. Common Vulnerabilities and Exposures (CVE) number has not
been assigned yet.
VIII. DISCLOSURE TIMELINE
09/30/2004 Initial vendor notification
09/30/2004 Initial vendor response
01/14/2005 Public disclosure
IX. CREDIT
The discoverer of this vulnerability wishes to remain anonymous.
Get paid for vulnerability research
http://www.idefense.com/poi/teams/vcp.jsp
X. LEGAL NOTICES
Copyright (c) 2004 iDEFENSE, Inc.
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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.
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