[UNIX] Exim auth_spa_server() Buffer Overflow Vulnerability
From: SecuriTeam (support_at_securiteam.com)
Date: 01/09/05
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To: list@securiteam.com Date: 9 Jan 2005 10:47:10 +0200
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Exim auth_spa_server() Buffer Overflow Vulnerability
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SUMMARY
<http://www.exim.org/> Exim is a message transfer agent developed for use
on UNIX systems. Remote exploitation of a buffer overflow vulnerability in
Exim 4.41 allows execution of arbitrary commands with elevated privileges.
DETAILS
Vulnerable Systems:
* Exim version 4.42 and prior
To determine if the Exim version being used is vulnerable, connect to port
25 of the machine with Exim installed and type:
EHLO localhost
If AUTH NTLM appears in the output the application may be vulnerable.
Immune Systems:
* Exim version 4.43 or newer
Details:
Exim is a message transfer agent developed for use on UNIX systems. The
problem specifically exists in the auth_spa_server function. The function
fails to check the length of input to spa_base64_to_bits(), which decodes
a Base64-encoded string into a buffer of a fixed length. This string is
user-controlled and passed to the program from a remote connection.
Analysis:
Exploitation of this vulnerability will give an attacker remote access to
the mailer uid. The Exim mailer is setuid root, but drops privileges
before the vulnerable code is reached. A remote attacker may be able to
use other vulnerabilities to further elevate their privileges.
This vulnerability is only exploitable when the spa authentication method
has been configured by setting AUTH_SPA=yes in Local/Makefile
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>
http://www.exim.org/mail-archives/exim-announce/2005/msg00000.html
The patch will be incorporated into a future Exim release (4.50).
CVE Information:
<http://www.cve.mitre.org/cgi-bin/cvename.cgi?name=CAN-2005-0022>
CAN-2005-0022
Disclosure Timeline:
12/23/2004 - Initial vendor notification
12/29/2004 - Initial vendor response
01/07/2004 - Coordinated public disclosure
ADDITIONAL INFORMATION
The information has been provided by
<mailto:idlabs-advisories@idefense.com> iDEFENSE.
The original article can be found at:
<http://www.idefense.com/application/poi/display?id=178&type=vulnerabilities> http://www.idefense.com/application/poi/display?id=178&type=vulnerabilities
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