Malformed Phonebook Entry Security Vulnerability in RAS Client

Microsoft Remote Access Service (RAS) client software may allow a user with the proper permissions to mount a denial-of-service attack or elevate his or her privileges on a RAS client computer.

This behavior occurs because the RAS client component that processes phonebook entries has an unchecked buffer. As a result, a specially malformed RAS phonebook entry can cause the RAS client to crash.

In very specific conditions, it can cause arbitrary code to run on the client computer. Because the RAS client operates in the security context of the local computer, the arbitrary code also runs in this context. This cannot occur accidentally.

Windows NT Server or Workstation 4.0

To resolve this problem, obtain the latest service pack for Windows NT 4.0 or the individual software update. For information on obtaining the latest service pack, please go to:

• http://www.microsoft.com/downloads/details.aspx?familyid=E396D059-E402-46EF-B095-A74399E25737&displaylang=en/ (http://www.microsoft.com/Windows/ServicePacks/) -or-
  
  
• 152734  (http://support.microsoft.com/kb/152734/EN-US/ ) how to obtain the latest windows nt 4.0 service pack

For information on obtaining the individual software update, contact Microsoft Product Support Services. For a complete list of Microsoft Product Support Services phone numbers and information on support costs, please go to the following address on the World Wide Web:

Windows NT Server 4.0, Terminal Server Edition

To resolve this problem, obtain the latest service pack for Windows NT Server 4.0, Terminal Server Edition. For additional information, click the following article number to view the article in the Microsoft Knowledge Base:

Microsoft has confirmed that this is a problem in the Microsoft products that are listed at the beginning of this article. This problem was first corrected in Windows NT Server version 4.0, Terminal Server Edition Service Pack 6.

This vulnerability affects only computers running the RAS client software; it does not affect RAS servers. A user must have permission to add or modify phonebook entries to initiate an attack. Permissions can be set using the phonebook's access control list (ACL).

Computers at risk because of this vulnerability are workstations that are configured to dial other computers as servers, including Microsoft Windows NT 4.0, Terminal Server Edition, but are not typically configured to act as RAS clients. This vulnerability affects only local computers; a user cannot directly attack remote computers.

For additional security-related information about Microsoft products, please visit the following Microsoft Web site: