Vulnerability Note VU#763400

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

Overview

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.

I. Description

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.

II. Impact

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.

III. Solution

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

Vendor	Status	Date Notified	Date Updated
Microsoft Corporation	Vulnerable	16-Jul-2001

References

http://www.ee.oulu.fi/research/ouspg/protos/testing/c06/ldapv3/
http://www.securityfocus.com/bid/3045
http://ciac.llnl.gov/ciac/bulletins/l-116.shtml
http://xforce.iss.net/static/6899.php

Credit

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

Date Public:	2001-07-16
Date First Published:	2001-07-16
Date Last Updated:	2002-12-12
CERT Advisory:	CA-2001-18
CVE-ID(s):	CAN-2001-1319
NVD-ID(s):	CAN-2001-1319
US-CERT Technical Alerts:
Metric:	6.14
Document Revision:	39

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