From:	 Florian Weimer <Florian.Weimer@RUS.Uni-Stuttgart.DE>
To:	 bugtraq@securityfocus.com
Subject: RUS-CERT Advisory 2001-09:01
Date:	 10 Sep 2001 16:53:52 +0200

Vulnerabilities in PAM and NSS modules using a PostgreSQL database

   During investigating the problem described in RUS-CERT Advisory
   2001-08:01, it became evident that a few PAM and NSS modules which use
   PostgreSQL as database backend are vulnerable to SQL code injections
   attacks, too.
   
  Systems Affected
  
   All systems using at least one of the following PAM and NSS modules:

     * libnss-pgsql 0.9.0 by Joerg Wendland
     * nss_postgresql 0.6.1 by Alessandro Gardich
     * pam-pgsql 0.9.2 by Joerg Wendland
     * pam_pgsql 0.0.3 by Alessandro Gardich
     * pam-pgsql 0.5.1 by Leon J Breedt
       
  Attack vector
  
   For the PAM authentication modules, the ability to attempt a
   password-based login on the system is required to exploit the
   vulnerability. The exact login method (HTTP Authentication, SSH,
   Telnet) does not matter, as long as PAM is used. For the NSS database
   modules, an interactive account is usually required to exploit this
   vulnerability.
   
  Impact
  
   The attack can execute arbitrary SQL statements under the database
   user used for querying the PostgreSQL database. Responses from the
   database backend can be faked. Exploiting the vulnerability in a PAM
   module, an attacker might gain unauthorized access. The possibilities
   of an attacker facing a vulnerable NSS module depend heavily on the
   system configuration and the offered services.
   
  Vulnerability Type
  
   SQL code insertion attack
   
  Description
  
   The problem as already been described in RUS-CERT Advisory 2001-08:01:
   An attacker might use specially crafted strings which contain embedded
   SQL statements to fake responses from the database backend. If the
   attacker can attempt logins using a suitable PAM-based login procedure
   (which permits spaces and single quotation marks in user names),
   involving one of the vulnerable PAM modules, or can query one of the
   NSS based handled by a vulnerable NSS module, he is able to execute
   arbitrary SQL statements on the database server, under the database
   user used for the query. In addition, data returned by queries can be
   manipulated. This can lead to unauthorized access to the system.
   
  Proposed Solution
  
   We believe that the fact that the essentially the same vulnerability
   is present in many PostgreSQL applications (see also RUS-CERT Advisory
   2001-08:01) is related to the lack of a suitable string quoting
   function in the PostgreSQL client library (and not just to code reuse
   and overlap among the authors).
   
   Therefore, we propose that a function which escapes characters treated
   specially by the PostgreSQL by replacing them with safe character
   sequences is included in the PostgreSQL client library. We provide a
   mostly untested sample implementation:

     * Escaping Strings in PostgreSQL Queries
       (http://cert.uni-stuttgart.de/doc/postgresql/escape/)
       
  Available Fixes
  
   Joerg Wendland has published fixed versions of his modules.

     * http://sourceforge.net/project/showfiles.php?group_id=24083
       
  Contact Status
  
   RUS-CERT contacted the authors of the vulnerable authentication
   modules on 2001-08-25.
   
  About RUS-CERT
  
   RUS-CERT (http://cert.uni-stuttgart.de/) is the Computer Emergency
   Response Team located at the Computing Center (RUS) of the
   University of Stuttgart, Germany.

  URI for this advisory

   http://cert.uni-stuttgart.de/advisories/postgresql_pam_nss.php

-- 
Florian Weimer 	                  Florian.Weimer@RUS.Uni-Stuttgart.DE
University of Stuttgart           http://cert.uni-stuttgart.de/
RUS-CERT                          +49-711-685-5973/fax +49-711-685-5898