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TUCoPS :: Windows Net Apps :: ciacj036.txt

MS Exchange LDAP Buffer Overflow



                       The U.S. Department of Energy
                    Computer Incident Advisory Capability
                           ___  __ __    _     ___
                          /       |     /_\   /
                          \___  __|__  /   \  \___

                             INFORMATION BULLETIN

           LDAP Buffer overflow against Microsoft Directory Services

March 16, 1999 19:00 GMT                                          Number J-036
PROBLEM:       ISS X-Force has a vulnerability against Microsoft Exchange's
               LDAP (Lightweight Directory Access Protocol) server which
               allows read access to the Exchange server directory by using an
               LDAP client.
PLATFORM:      Microsoft Exchange Server version 5.5.
DAMAGE:        If exploited, an attacker could cause a buffer overflow which
               could lead to a denial of service or allow the attacker to be
               able to execute arbitrary code.
SOLUTION:      Apply patch or workaround.
VULNERABILITY  Risk is medium. The packet to cause the buffer overflow would
ASSESSMENT:    have to be a particular type or carefully crafted.

[  Start ISS Advisory  ]

ISS Security Advisory
March 15, 1999

LDAP Buffer overflow against Microsoft Directory Services


ISS X-Force has discovered a buffer overflow exploit against Microsoft
Exchange's LDAP (Lightweight Directory Access Protocol) server which
allows read access to the Exchange server directory by using an LDAP
client.  This buffer overflow consists of a malformed bind request that
overflows the buffer and can execute arbitrary code. This attack can also
cause the Exchange LDAP service to crash. This vulnerability exists in
Microsoft Exchange Server version 5.5.


This exploit occurs during the LDAP binding process. Binding involves
logging in or authenticating to a directory, and consists of sending a
username, a password, and a binding method. There are two methods in
which to use this vulnerability against an Exchange server. The first
consists of sending a particular type of invalid LDAP bind packet which
will cause an overflow to occur this will cause the LDAP service to crash.
The second uses a large malformed LDAP bind packet that is carefully
crafted to take advantage of the buffer overflow and can be used to
execute arbitrary code.


Microsoft has made a patch available for the LDAP attack.  Patch
information is available at:

Network administrators can protect internal systems from external attack
by adding a rule to a filtering router or firewall of the type: Deny all
incoming TCP packets with a destination port of 389.

Many firewalls or packet filters may already have more restrictive
rulesets that already encompass this filtering rule, in which case the
network is already protected from an external attack.  This ruleset would
include filtering all incoming traffic to TCP port 389.

Additional Information:

These vulnerabilities were primarily researched by the ISS X-Force.


Copyright (c) 1999 by Internet Security Systems, Inc.

Permission is hereby granted for the electronic redistribution of this
Security Advisory.  It is not to be edited in any way without express
consent of the X-Force.  If you wish to reprint the whole or any part of
this Security Advisory in any other medium excluding electronic medium,
please e-mail for permission.

Internet Security Systems, Inc. (ISS) is the leading provider of adaptive
network security monitoring, detection, and response software that
protects the security and integrity of enterprise information systems.  By
dynamically detecting and responding to security vulnerabilities and
threats inherent in open systems, ISS's SAFEsuite family of products
provide protection across the enterprise, including the Internet,
extranets, and internal networks, from attacks, misuse, and security
policy violations.  ISS has delivered its adaptive network security
solutions to organizations worldwide, including firms in the Global 2000,
nine of the ten largest U.S. commercial banks, and over 35 governmental
agencies.  For more information, call ISS at 678-443-6000 or 800-776-2362
or visit the ISS Web site at

The information within this paper may change without notice. Use of this
information constitutes acceptance for use in an AS IS condition. There
are NO warranties with regard to this information. In no event shall the
author be liable for any damages whatsoever arising out of or in
connection with the use or spread of this information. Any use of this
information is at the user's own risk.

X-Force PGP Key available at: as
well as on MIT's PGP key server and's key server.

X-Force Vulnerability and Threat Database:

Please send suggestions, updates, and comments to:
X-Force <> of Internet Security Systems, Inc.

[  End ISS Advisory  ]

CIAC wishes to acknowledge the contributions of Internet Security Systems,
Inc. 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
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