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Category:   Application (E-mail Server)  >   Exim Vendors:   Exim.org
Exim Buffer Overflow in dns_build_reverse() Lets Local Users Obtain Elevated Privileges
SecurityTracker Alert ID:  1012904
SecurityTracker URL:  http://securitytracker.com/id/1012904
CVE Reference:   GENERIC-MAP-NOMATCH   (Links to External Site)
Date:  Jan 14 2005
Impact:   Execution of arbitrary code via local system, User access via local system
Fix Available:  Yes  Vendor Confirmed:  Yes  
Version(s): 4.43 and prior versions
Description:   iDEFENSE reported a buffer overflow vulnerability in Exim in the dns_build_reverse() function. A local user can obtain elevated privileges.

A local user can supply a specially crafted command line option to trigger the overflow and execute arbitrary code. A demonstration exploit is provided:

/usr/bin/exim -bh ::%A`perl -e 'print pack('L',0xdeadbeef') x 256'`

The code will run with the privileges of the Exim mailer.

The vendor was notified on September 30, 2004.

The original advisory is available at:

http://www.idefense.com/application/poi/display?id=183&type=vulnerabilities

Impact:   A local user can execute arbitrary code with the privileges of the Exim mailer.
Solution:   The vendor has issued a patch for Exim 4.43, available at:

http://www.exim.org/mail-archives/exim-announce/2005/msg00000.html

Vendor URL:  www.exim.org/ (Links to External Site)
Cause:   Boundary error
Underlying OS:  Linux (Any), UNIX (Any)

Message History:   None.


 Source Message Contents

Subject:  iDEFENSE Security Advisory 01.14.05: Exim dns_buld_reverse() Buffer


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.

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.
 
 


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