Exim host_aton() Buffer Overflow Vulnerability

iDEFENSE Security Advisory [IDEF0725]
http://www.idefense.com/application/poi/display?type=vulnerabilities
January 07, 2005

I. BACKGROUND

Exim is a message transfer agent developed for use on Unix systems. More

information is available at: 

  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 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.

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 e-mail messages or possibly further 
elevation.

IV. 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.

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

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.

VIII. DISCLOSURE TIMELINE

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