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. Get paid for vulnerability research http://labs.idefense.com/methodology/vulnerability/vcp.php Free tools, research and upcoming events http://labs.idefense.com/ X. LEGAL NOTICES Copyright © 2009 iDefense, Inc. Permission is granted for the redistribution of this alert electronically. It may not be edited in any way without the express written consent of iDefense. If you wish to reprint the whole or any part of this alert in any other medium other than electronically, please e-mail customerservice@idefense.com for permission. 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.