Samba SAMR Change Password Remote Command Injection Vulnerability

iDefense Security Advisory 05.14.07
http://labs.idefense.com/intelligence/vulnerabilities/
May 14, 2007

I. BACKGROUND

Samba is a Unix server application used to implement Windows file
sharing and domain controlling functionality. SAMR is the named pipe
used to access the SAM, security accounts manager, database. This
database stores login credentials on NT based systems. More information
can be found at the following URL.

http://samba.org/samba/

II. DESCRIPTION

Remote exploitation of a command injection vulnerability within Samba
Project's Samba could allow an attacker to execute arbitrary code with
nobody privileges.

The vulnerability exists within the code responsible for updating a
user's password in the SAM database. Unfiltered user input is passed to
"/bin/sh". This allows an attacker to execute arbitrary shell commands
with the privileges of the nobody user.

III. ANALYSIS

Successful exploitation of this vulnerability allows an attacker to run
arbitrary shell commands with the privileges of the nobody user.

An important mitigating factor is that this vulnerability occurs within
a non-default configuration of Samba. Specifically, the 'username map
script' option must be defined in the smb.conf file.

Valid credentials are not needed to exploit this vulnerability. In order
to successfully change a password, it is necessary to provide the
original password. However, the vulnerability can still be triggered
regardless of whether or not the change password attempt fails.

IV. DETECTION

iDefense has confirmed the existence of this vulnerability in Samba
version 3.0.24. Previous versions of Samba release 3 may be vulnerable.
Release version 2 and below did not have this feature.

V. WORKAROUND

Removing the 'username map script' option from the smb.conf file will
prevent this vulnerability from being triggered.

VI. VENDOR RESPONSE

Samba has released version 3.0.25 as well as a patch for version 3.0.24
to address this issue. More information can be found in their
announcement at the following URL.

http://samba.org/samba/security/CVE-2007-2447.html

VII. CVE INFORMATION

The Common Vulnerabilities and Exposures (CVE) project has assigned the
name CVE-2007-2447 to this issue. This is a candidate for inclusion in
the CVE list (http://cve.mitre.org/), which standardizes names for
security problems.

VIII. DISCLOSURE TIMELINE

05/07/2007  Initial vendor notification
05/07/2007  Initial vendor response
05/14/2007  Coordinated public disclosure

IX. CREDIT

The discoverer of this vulnerability wishes to remain anonymous.

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X. LEGAL NOTICES

Copyright © 2007 iDefense, Inc.

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Disclaimer: The information in the advisory is believed to be accurate
at the time of publishing based on currently available information. Use
of the information constitutes acceptance for use in an AS IS condition.
 There are no warranties with regard to this information. Neither the
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