Vulnerability Note VU#763400

Microsoft Exchange LDAP Service is vulnerable to denial-of-service attacks

Original Release date: 16 Jul 2001 | Last revised: 12 Dec 2002


The Microsoft Exchange LDAP Service contains vulnerabilities that may allow denial-of-service attacks. These vulnerabilities were revealed using the PROTOS LDAPv3 test suite and are documented in CERT Advisory CA-2001-18. If your site uses this product, the CERT/CC encourages you to follow the advice provided below.


The LDAP Service components of Microsoft Exchange 5.5 and Exchange 2000 contain vulnerabilities that cause affected LDAP servers to freeze in response to malformed LDAP requests generated by the PROTOS test suite. This only affects the LDAP service; all other Exchange services, including mail handling, continue normally.

Although these products were not included in OUSPG's initial testing, subsequent informal testing revealed that the LDAP service of Microsoft Exchange became unresponsive while processing test cases containing exceptional BER encodings for the LDAP filter type field.


These vulnerabilities allow a remote attacker to crash the LDAP component of vulnerable Exchange 5.5 and Exchange 2000 servers, resulting in a denial-of-service condition within the LDAP component.


Apply a patch from your vendor

Please consult the vendor section for vendor-specific information on addressing this vulnerability.

Block access to directory services at network perimeter

As a temporary measure, it is possible to limit the scope of these vulnerabilities by blocking access to directory services at the network perimeter. Please note that this workaround does not protect vulnerable products from internal attacks.

            ldap    389/tcp     # Lightweight Directory Access Protocol
            ldap    389/udp     # Lightweight Directory Access Protocol
            ldaps   636/tcp     # ldap protocol over TLS/SSL (was sldap)
            ldaps   636/udp     # ldap protocol over TLS/SSL (was sldap)

Disable anonymous LDAP access

Microsoft has reported that "It is important to note that this issue can be mitigated by disabling anonymous authentication."

Systems Affected (Learn More)

VendorStatusDate NotifiedDate Updated
Microsoft CorporationAffected31 May 200116 Jul 2001
If you are a vendor and your product is affected, let us know.

CVSS Metrics (Learn More)

Group Score Vector
Base N/A N/A
Temporal N/A N/A
Environmental N/A N/A



The CERT Coordination Center thanks the Oulu University Secure Programming Group for reporting these vulnerabilities to us, for their detailed technical analyses, and for their assistance in preparing this document.

This document was written by Jeffrey P. Lanza.

Other Information

  • CVE IDs: CAN-2001-1319
  • CERT Advisory: CA-2001-18
  • Date Public: 16 Jul 2001
  • Date First Published: 16 Jul 2001
  • Date Last Updated: 12 Dec 2002
  • Severity Metric: 6.14
  • Document Revision: 39


If you have feedback, comments, or additional information about this vulnerability, please send us email.