January 2005

ID: 00014
Ref: 14/2005
Date: 10 January 2005:14:47:40
Version: 1

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Title: Two iDEFENSE Security Advisories: 1. [IDEF0731] - Exim auth_spa_server() Buffer Overflow Vulnerability 2. [IDEF0725] - Exim host_aton() Buffer Overflow Vulnerability
Abstract:
Vendors affected: idefense
Operating systems affected: idefense
Applications affected: idefense

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Title
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Two iDEFENSE Security Advisories:

1. [IDEF0731] - Exim auth_spa_server() Buffer Overflow Vulnerability

2. [IDEF0725] - Exim host_aton() Buffer Overflow Vulnerability


Detail
======

1. 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.

2. Local exploitation of a buffer overflow vulnerability in Exim 4.41 may
allow execution of arbitrary commands with elevated privileges.



1.



Exim auth_spa_server() Buffer Overflow Vulnerability

iDEFENSE Security Advisory [IDEF0731]
www.idefense.com/application/poi/display?id=178&type=vulnerabilities
January 07, 2004

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

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
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.

III. 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
when building it.

IV. DETECTION

Exim versions 4.40 and 4.41 have been confirmed vulnerable. The source
code for version 4.42 suggests that it is vulnerable. It is suspected
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
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
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.



2.


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.

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.