Date: Fri, 7 Jan 2005 17:02:09 -0500
From: customer service mailbox <customerservice@idefense.com.>
To: [email protected], [email protected]Subject: iDEFENSE Security Advisory [IDEF0731] Exim auth_spa_server() Buffer Overflow Vulnerability
Exim auth_spa_server() Buffer Overflow Vulnerability=20
iDEFENSE Security Advisory [IDEF0731]
www.idefense.com/application/poi/display?id=3D178&type=3Dvulnerabilities
January 07, 2004
I. BACKGROUND
Exim is a message transfer agent developed for use on Unix systems. More
information is available at:=20
http://www.exim.org/
II. DESCRIPTION
Remote exploitation of a buffer overflow vulnerability in Exim 4.41 may
allow execution of arbitrary commands with elevated privileges.
Exim is a message transfer agent developed for use on Unix systems. The=20
problem specifically exists in the auth_spa_server function. The=20
function fails to check the length of input to spa_base64_to_bits(),=20
which decodes a Base64-encoded string into a buffer of a fixed length.=20
This string is user-controlled and passed to the program from a remote=20
connection.
III. ANALYSIS
Exploitation of this vulnerability will give an attacker remote access=20
to the mailer uid. The exim mailer is setuid root, but drops privileges=20
before the vulnerable code is reached. A remote attacker may be able to=20
use other vulnerabilities to further elevate their privileges.
This vulnerability is only exploitable when the spa authentication=20
method has been configured by setting AUTH_SPA=3Dyes in Local/Makefile=20
when building it.
IV. DETECTION
Exim versions 4.40 and 4.41 have been confirmed vulnerable. The source=20
code for version 4.42 suggests that it is vulnerable. It is suspected=20
that previous versions are also vulnerable.
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.
V. WORKAROUND
iDEFENSE is currently unaware of any effective workarounds for this=20
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-2005-0022 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
01/07/2004 Coordinated 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 [email protected] 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.
