7083513 2001-09-10 16:53 +0200 /99 rader/ Florian Weimer <Florian.Weimer@RUS.Uni-Stuttgart.DE>
Sänt av: joel@lysator.liu.se
Importerad: 2001-09-11 00:44 av Brevbäraren
Extern mottagare: bugtraq@securityfocus.com
Mottagare: Bugtraq (import) <19141>
Ärende: RUS-CERT Advisory 2001-09:01
------------------------------------------------------------
From: Florian Weimer <Florian.Weimer@RUS.Uni-Stuttgart.DE>
To: bugtraq@securityfocus.com
Message-ID: <tgd74zgkqn.fsf@mercury.rus.uni-stuttgart.de>
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
(7083513) /Florian Weimer <Florian.Weimer@RUS.Uni-Stuttgart.DE>/(Ombruten)