__________________________________________________________ The U.S. Department of Energy Computer Incident Advisory Capability ___ __ __ _ ___ / | /_\ / \___ __|__ / \ \___ __________________________________________________________ INFORMATION BULLETIN Microsoft Server Response To SMTP Client EHLO Command Results In Buffer Overrun [Microsoft Security Bulletin MS02-037] July 26, 2002 14:00 GMT Number M-100 ______________________________________________________________________________ PROBLEM: The Internet Mail Connector (IMC) component of the Microsoft Exchange Server has an unchecked buffer. The IMC enables the Exchange Server to communicate with other mail servers via SMTP. PLATFORM: Those running Microsoft Exchange Server 5.5 DAMAGE: This vulnerability may allow users to cause the IMC to fail. Users could also run arbitrary code in the security context of the IMC, which runs as Exchange5.5 Service Account. SOLUTION: Apply the patch as directed by the advisory. ______________________________________________________________________________ VULNERABILITY The risk is LOW. Microsoft states that exploiting the ASSESSMENT: vulnerability would be quite difficult. ______________________________________________________________________________ LINKS: CIAC BULLETIN: http://www.ciac.org/ciac/bulletins/m-100.shtml ORIGINAL BULLETIN: http://www.microsoft.com/technet/treeview/default.asp?url=/technet/security/bulletin/MS02-037.asp ______________________________________________________________________________ [***** Start Microsoft Security Bulletin MS02-037 *****] Microsoft Security Bulletin MS02-037 Server Response To SMTP Client EHLO Command Results In Buffer Overrun (Q326322) Originally posted: July 24, 2002 Summary Who should read this bulletin: System administrators using Microsoft Exchange Server 5.5. Impact of vulnerability: Ability to run arbitrary code Maximum Severity Rating: Moderate Recommendation: System administrators should consider applying the patch. Affected Software: Microsoft Exchange Server 5.5 Technical details Technical description: The Internet Mail Connector (IMC) enables Microsoft Exchange Server to communicate with other mail servers via SMTP. When the IMC receives an SMTP extended Hello (EHLO) protocol command from a connecting SMTP server, it responds by sending a status reply that starts with the following: 250-Hello Where: * is the fully-qualified domain name (FQDN) of the Exchange server * is either the FQDN or the IP address of the server that initiated the connection. The FQDN would be used if the Exchange5.5 IMC is able to resolve this information through a reverse DNS lookup; the IP address would be used if a reverse DNS lookup was not possible or failed to resolve the connecting servers IP address. A security vulnerability results because of an unchecked buffer in the IMC code that generates the response to the EHLO protocol command. If the total length of the message exceeds a particular value, the data would overrun the buffer. If the buffer were overrun with random data, it would result in the failure of the IMC. If, however, the buffer were overrun with carefully chosen data, it could be possible for the attacker to run code in the security context of the IMC, which runs as Exchange5.5 Service Account. It is important to note that the attacker could not simply send data to the IMC in order to overrun the buffer. Instead, the attacker would need to create a set of conditions that would cause the IMC to overrun its own buffer when it generated the EHLO response. Specifically, the attacker would need to ensure that a reverse DNS lookup would not only succeed, but would provide an FQDN whose length was sufficient to result in the buffer overrun. Mitigating factors: * Creating an environment in which the IMC's reverse DNS lookup would not only succeed but also result in the buffer being overrun would be difficult. The attacker could set up a rogue DNS server and manually populate the bogus FQDN information on it, but in this would require that the attacker have some means of forcing the IMC to consult the rogue DNS server when performing the reverse DNS lookup. * The IMC can be disabled for cases where SMTP support is not needed. If this has been done, the vulnerability could not be exploited. * Customers can disable Reverse DNS lookup on EHLO by setting a registry key as defined in Q190026. The vulnerability could not be exploited on a system configured in such a way. * If the buffer overrun caused the IMC to fail, normal service could be restored by restarting the Exchange 5.5 IMC service. Severity Rating: | Internet Servers | Intranet Servers | Client Systems | Exchange 5.5 SP4 | Moderate | Moderate | None | 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. We have rated this vulnerability as a moderate one because of the difficulty of exploiting the vulnerability. Vulnerability identifier: CAN-2002-0698 Tested Versions: Microsoft tested Exchange 2000 and Exchange 5.5 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. Patch availability Download locations for this patch * Microsoft Exchange 5.5 Service Pack 4: http://www.microsoft.com/Downloads/Release.asp?ReleaseID=40666 Additional information about this patch Installation platforms: This patch can be installed on systems running Microsoft Exchange 5.5 Service Pack 4. Inclusion in future service packs: None Reboot needed: No Patch can be uninstalled: Yes Superseded patches: None. Verifying patch installation: * 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\Exchange Server 5.5\SP5\Q326322 * To verify the individual files, use the date/time and version information provided in the following registry key: HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Updates\Exchange Server 5.5\SP5\Q326322\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 Other information: Acknowledgments Microsoft thanks Dan Ingevaldson of Internet Security Systems for reporting this issue to us and working with us to protect customers. Support: * Microsoft Knowledge Base article Q326322 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 (July 24, 2002): Bulletin Created. * V1.1 (July 25, 2002): Changed to indicate that patch can be uninstalled. [***** End Microsoft Security Bulletin MS02-037 *****] _______________________________________________________________________________ CIAC wishes to acknowledge the contributions of Microsoft Corporation 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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