__________________________________________________________ The U.S. Department of Energy Computer Incident Advisory Capability ___ __ __ _ ___ / | /_\ / \___ __|__ / \ \___ __________________________________________________________ INFORMATION BULLETIN MS Heap Overrun in HTR Chunked Encoding Vulnerability [Microsoft Security Bulletin MS02-028 ] June 13, 2002 18:00 GMT Number M-089 ______________________________________________________________________________ PROBLEM: This vulnerability involves a buffer overrun in the Chunked Encoding data transfer mechanism in IIS 4.0 and 5.0. It could be used to overrun heap memory on the system, with the result of either causing the IIS service to fail or allowing code to be run on the server. PLATFORM: Any operating system running: * Microsoft Internet Information Server 4.0 * Microsoft Internet Information Services 5.0 DAMAGE: The vulnerability could grant varying degrees of control to a successful attacker, either causing the IIS service to fail or allowing code to be run on the server. SOLUTION: Apply available patches. ______________________________________________________________________________ VULNERABILITY The risk is MEDIUM. Depending on the particular version in use, ASSESSMENT: a server configured using any of the Microsoft security checklists or security tools would not have the HTR functionality enabled. ______________________________________________________________________________ LINKS: CIAC BULLETIN: http://www.ciac.org/ciac/bulletins/m-089.shtml ORIGINAL BULLETIN: http://microsoft.com/technet/treeview/default.asp?url=/technet/security/bulletin/MS02- 028.asp PATCHES: Microsoft IIS 4.0: http://www.microsoft.com/Downloads/Release.asp?ReleaseID=39579 Microsoft IIS 5.0: http://www.microsoft.com/Downloads/Release.asp?ReleaseID=39217 ______________________________________________________________________________ [***** Start Microsoft Security Bulletin MS02-028 *****] Microsoft Security Bulletin MS02-028 Heap Overrun in HTR Chunked Encoding Could Enable Web Server Compromise (Q321599) Originally posted: June 12, 2002 Summary Who should read this bulletin: Customers hosting web servers using Microsoft® Windows NT® 4.0 or Windows® 2000. Impact of vulnerability: Run code of an attacker's choice on the system Maximum Severity Rating: Moderate Recommendation: Customers who have a business-critical reason for retaining HTR scripting should apply the patch immediately. All others should ensure HTR is disabled. Affected Software: Microsoft Internet Information Server 4.0 Microsoft Internet Information Services 5.0 Technical details Technical description: This patch eliminates a newly discovered vulnerability affecting Internet Information Services. Although Microsoft typically delivers cumulative patches for IIS, in this case we have delivered a patch that eliminates only this new vulnerability, while completing a cumulative patch. When the cumulative patch is customer-ready, we will update this bulletin with information on its availability. The FAQ provides information on the circumstances surrounding the vulnerability, and why we believe releasing a singleton patch immediately is in customers' best interests. To ensure that servers are fully protected against past as well as current vulnerabilities, we strongly recommend installing the previous cumulative patch (discussed in Microsoft Security Bulletin MS02-018) before installing this patch. The vulnerability is similar to the first vulnerability discussed in Microsoft Security Bulletin MS02-018. Like that vulnerability, this one involves a buffer overrun in the Chunked Encoding data transfer mechanism in IIS 4.0 and 5.0, and could likewise be used to overrun heap memory on the system, with the result of either causing the IIS service to fail or allowing code to be run on the server. The chief difference between the vulnerabilities is that the newly discovered one lies in the ISAPI extension that implements HTR – an older, largely obsolete scripting technology – where the previous one lay in the ISAPI extension that implements ASP. Mitigating factors: Microsoft has long recommended disabling HTR functionality unless there is a business- critical reason for retaining it. Systems on which HTR is disabled would not be at risk from this vulnerability. The IIS Lockdown Tool disables HTR by default in all server configurations. The current version of the URLScan tool provides a means of blocking chunked encoding transfer requests by default. On default installations of IIS 5.0, exploiting the vulnerability to run code would grant the attacker the privileges of the IWAM_computername account, which has only the privileges commensurate with those of an interactively logged-on unprivileged user. Severity Rating: Internet Servers Intranet Servers Client Systems IIS 4.0 Moderate Moderate Moderate IIS 5.0 Moderate Moderate Moderate The above assessment is based on the types of systems affected by the vulnerability, their typical deployment patterns, and the effect that exploiting the vulnerability would have on them. Although the vulnerability would grant varying degrees of control to a successful attacker, depending on the particular version in use, a server configured using any of the Microsoft security checklists or security tools would not have the HTR functionality enabled. Vulnerability identifier: CAN-2002-0364 Tested Versions: Microsoft tested IIS 4.0, 5.0 and 5.1 to assess whether they are affected by these vulnerabilities. Previous versions are no longer supported, and may or may not be affected by these vulnerabilities. IIS 6.0 is a beta product, and beta products are typically not eligible for security patches; however, we have confirmed that no beta versions of IIS 6.0 are affected by the vulnerability. Patch availability Download locations for this patch Microsoft IIS 4.0: http://www.microsoft.com/Downloads/Release.asp?ReleaseID=39579 Microsoft IIS 5.0: http://www.microsoft.com/Downloads/Release.asp?ReleaseID=39217 Additional information about this patch Installation platforms: The IIS 4.0 patch can be installed on systems running Windows NT 4.0 Service Pack 6a. The IIS 5.0 patch can be installed on systems running Windows 2000 Service Pack 1 or Service Pack 2. Inclusion in future service packs: No additional service packs are planned for Windows NT 4.0. The IIS 5.0 fix will be included in Windows 2000 Service Pack 3. Reboot needed: IIS 4.0: A reboot can be avoid by stopping the IIS service, installing the patch with the /z switch, then restarting the service. Knowledge Base article Q319733 provides additional information on this procedure. IIS 5.0: No. Superseded patches: None. Verifying patch installation: IIS 4.0: To verify that the patch has been installed on the machine, confirm that the following registry key has been created on the machine: HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Windows NT\CurrentVersion\Hotfix\Q321599. To verify the individual files, consult the file manifest in Knowledge Base article Q321599. IIS 5.0: To verify that the patch has been installed on the machine, confirm that the following registry key has been created on the machine: HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Updates\Windows 2000\SP3\Q321599. To verify the individual files, use the date/time and version information provided in the following registry key: HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Updates\Windows 2000\SP3\Q321599\Filelist. Caveats: None Localization: Localized versions of this patch are available at the locations discussed in "Patch Availability". Obtaining other security patches: Patches for other security issues are available from the following locations: Security patches are available from the Microsoft Download Center, and can be most easily found by doing a keyword search for "security_patch". Patches for consumer platforms are available from the WindowsUpdate web site All patches available via WindowsUpdate also are available in a redistributable form from the WindowsUpdate Corporate site. Other information: Acknowledgments Microsoft thanks eEye Digital Security for reporting this issue to us and working with us to protect customers. Support: Microsoft Knowledge Base article Q321599 discusses this issue and will be available approximately 24 hours after the release of this bulletin. Knowledge Base articles can be found on the Microsoft Online Support web site. Technical support is available from Microsoft Product Support Services. There is no charge for support calls associated with security patches. Security Resources: The Microsoft TechNet Security Web Site provides additional information about security in Microsoft products. Disclaimer: The information provided in the Microsoft Knowledge Base is provided "as is" without warranty of any kind. Microsoft disclaims all warranties, either express or implied, including the warranties of merchantability and fitness for a particular purpose. In no event shall Microsoft Corporation or its suppliers be liable for any damages whatsoever including direct, indirect, incidental, consequential, loss of business profits or special damages, even if Microsoft Corporation or its suppliers have been advised of the possibility of such damages. Some states do not allow the exclusion or limitation of liability for consequential or incidental damages so the foregoing limitation may not apply. Revisions: V1.0 (June 12, 2002): Bulletin Created. [***** End Microsoft Security Bulletin MS02-028 *****] _______________________________________________________________________________ CIAC wishes to acknowledge the contributions of Microsoft for the information contained in this bulletin. _______________________________________________________________________________ CIAC, the Computer Incident Advisory Capability, is the computer security incident response team for the U.S. Department of Energy (DOE) and the emergency backup response team for the National Institutes of Health (NIH). CIAC is located at the Lawrence Livermore National Laboratory in Livermore, California. CIAC is also a founding member of FIRST, the Forum of Incident Response and Security Teams, a global organization established to foster cooperation and coordination among computer security teams worldwide. CIAC services are available to DOE, DOE contractors, and the NIH. CIAC can be contacted at: Voice: +1 925-422-8193 (7x24) FAX: +1 925-423-8002 STU-III: +1 925-423-2604 E-mail: ciac@ciac.org Previous CIAC notices, anti-virus software, and other information are available from the CIAC Computer Security Archive. World Wide Web: http://www.ciac.org/ Anonymous FTP: ftp.ciac.org PLEASE NOTE: Many users outside of the DOE, ESnet, and NIH computing communities receive CIAC bulletins. If you are not part of these communities, please contact your agency's response team to report incidents. Your agency's team will coordinate with CIAC. The Forum of Incident Response and Security Teams (FIRST) is a world-wide organization. A list of FIRST member organizations and their constituencies can be obtained via WWW at http://www.first.org/. This document was prepared as an account of work sponsored by an agency of the United States Government. Neither the United States Government nor the University of California nor any of their employees, makes any warranty, express or implied, or assumes any legal liability or responsibility for the accuracy, completeness, or usefulness of any information, apparatus, product, or process disclosed, or represents that its use would not infringe privately owned rights. Reference herein to any specific commercial products, process, or service by trade name, trademark, manufacturer, or otherwise, does not necessarily constitute or imply its endorsement, recommendation or favoring by the United States Government or the University of California. The views and opinions of authors expressed herein do not necessarily state or reflect those of the United States Government or the University of California, and shall not be used for advertising or product endorsement purposes. 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