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TUCoPS :: Windows Net Apps :: m-100.txt

Microsoft Server Response To SMTP Client EHLO Command Results In Buffer Overrun (CIAC M-100)


                       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
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.
 ORIGINAL BULLETIN:                                                           

[***** 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


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-<Exchange server ID>Hello<Connecting server ID>


* <Exchange server ID> is the fully-qualified domain name (FQDN) of the Exchange

* <Connecting server ID> 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:

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:


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




Localized versions of this patch are available at the locations discussed in "Patch

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:


Microsoft thanks  Dan Ingevaldson of Internet Security Systems for reporting this
issue to us and working with us to protect customers.


* 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.


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.


* 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.

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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
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