Apache auth_ldap module Multiple Format Strings Vulnerability

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Digital Armaments advisory is 12.22.2005

I. Background

auth_ldap is an LDAP authentication module for Apache, the world's most popular web server. auth_ldap has excellent performance, and supports Apache on both Unix and Windows NT. It also has support for LDAP over SSL, and a mode that lets Microsoft Frontpage clients manage their web permissions while still using LDAP for authentication.
For further information or detail about the software you can refer to the vendor's homepage:

http://www.rudedog.org/auth_ldap/

II. Problem Description

Due to an insecure usage of the function apache logging function (ap_log_rerror) in auth_ldap_log_reason function it's possible to run arbitrary code on the server running the module. For example this can generate a custom format string that can be supplied by the attacker through the username given during the apache authentication process but several parts of the module are affected.

III. Detection

This problem has been detected on latest version of auth_ldap 1.6.0 and on prior versions from 1.2.x. It persists on all platforms where auth_ldap can be compiled.

IV. Impact analysis

Successful exploitation allows an attacker to gain access to the system. Exploit code is required.

V. Solution

First notification 12.22.2005.
Second notification 01.09.2006.
The vendor answered second notification.
A new patched version will be available.

VI. Credit

Seregorn - seregon@bughunter.net is credited with this discovery.

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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 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.