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
Block access to directory services at network perimeter
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.