De: "Florian Weimer" À: Objet: RUS-CERT Advisory 2001-09:01 Date : lundi 10 septembre 2001 22:51 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