[Full-disclosure] iDefense Security Advisory 06.11.09: Microsoft Active Directory Hexdecimal DN AttributeValue Invalid Free Vulnerability

[iDefense Labs <labs-no-reply@xxxxxxxxxxxx>]

iDefense Security Advisory 06.11.09
http://labs.idefense.com/intelligence/vulnerabilities/
Jun 11, 2009

I. BACKGROUND

Active Directory, created by Microsoft Corp., provides a number of
network services, one of which is a Light-weight Directory Access
Protocol (LDAP) compatible directory service.

II. DESCRIPTION

Remote exploitation of an invalid free vulnerability in Microsoft
Corp.'s Active Directory Server allows attackers to exhaust all virtual
memory.

According to section 2.4 of the IETF Request For Comments (rfc) 4514,
LDAP requests can contain strings that have been encoded using
hexadecimal encoding. When Active Directory on Windows 2000 encounters
such a request, it fails to release the memory associated with the
hexadecimal encoded portion of the request. By continually making such
requests, an attacker can exhaust virtual memory on the targeted
system.

III. ANALYSIS

Exploitation allows an attacker to consume all available virtual memory
on the affected system. To exploit this vulnerability, an attacker must
be able to establish a TCP session with the vulnerable machine. LDAP
uses port 389 or, when encrypted, port 636. Additionally, LDAP requests
are processed when connecting to the Global Catalog Server on ports 3268
or 3269.

Although exhausting virtual memory does not compromise the integrity of
the system, it can allow some otherwise non-exploitable vulnerabilities
to be exploited. As long as virtual memory is exhausted, the computer
will not be able to start new programs, or do other tasks that require
allocating virtual memory.

IV. DETECTION

iDefense confirmed the existence of this vulnerability using a Windows
2000 SP4 domain controller with all patches available as of January
2008 applied. All versions of Active Directory installed on Windows
2000 are suspected to be vulnerable.

V. WORKAROUND

Employing firewalls to limit access to the affected services will
mitigate exposure to this vulnerability.

VI. VENDOR RESPONSE

Microsoft has released a patch which addresses this issue. For more
information, consult their advisory at the following URL:

http://www.microsoft.com/technet/security/Bulletin/MS09-018.mspx

VII. CVE INFORMATION

The Common Vulnerabilities and Exposures (CVE) project has assigned the
name CVE-2009-1138 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

01/21/2009  - Initial Contact
01/22/2009  - Initial Response
01/27/2009  - Requested PoC
01/30/2009  - Sent PoC
02/09/2009  - MS Status update
06/02/2009  - MS Requests Credit request
06/04/2009  - CVE Received
06/04/2009  - iDefense Requested CVE
06/05/2009  - Microsoft informs iDefense that the Bulletin was promoted
to potential Code Execution
06/08/2009  - iDefense requests clarification, offers further insight
06/10/2009  - iDefense reiterates request
06/10/2009  - MS Responds that they agree that code execution is very
unlikely and will change the Exploitability Index
06/11/2009  - MS Changes Exploitability Index from 1 to 3
06/11/2009  - Coordinated public disclosure

IX. CREDIT

This vulnerability was discovered by Joshua J. Drake of iDefense Labs.

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X. LEGAL NOTICES

Copyright © 2009 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
author nor the publisher accepts any liability for any direct,
indirect, or consequential loss or damage arising from use of, or
reliance on, this information.

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