DOCUMENT:Q230677 TITLE :Malformed Phonebook Entry Security Vulnerability in RAS Client PRODUCT :Windows NT PROD/VER:4.0 OPER/SYS:WINDOWS NT KEYWORD :kbbug4.00 kbfix4.00 ------------------------------------------------------------------------------- The information in this article applies to: - Microsoft Windows NT Workstation versions 4.0, 4.0 SP1, 4.0 SP2, 4.0 SP3, 4.0 SP4 - Microsoft Windows NT Server versions 4.0, 4.0 SP1, 4.0 SP2, 4.0 SP3, 4.0 SP4 - Microsoft Windows NT Server, Enterprise Edition versions 4.0, 4.0 SP4 ------------------------------------------------------------------------------- SYMPTOMS ======== A specially malformed phonebook entry may be used to exploit a security vulnerability on a computer that has the Microsoft Remote Access Service (RAS) client software installed. A user with the proper permissions can abuse this vulnerability to run a program and cause a denial of service attack or privilege escalation attack on the RAS client computer. CAUSE ===== The RAS client component that processes phonebook entries has an unchecked buffer. As a result, a uniquely formed RAS phonebook entry can execute a program via a buffer overrun situation on the RAS client computer. Since the RAS client runs in the security context of the local computer, the rogue program also runs in this context. Because of the nature of this exploit, this issue cannot occur accidentally. RESOLUTION ========== A supported fix that corrects this problem is now available from Microsoft, but it has not been fully regression tested and should be applied only to systems experiencing this specific problem. If you are not severely affected by this specific problem, Microsoft recommends that you wait for the next Windows NT 4.0 service pack that contains this fix. To resolve this problem immediately, contact Microsoft Product Support Services to obtain the fix. 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: http://support.microsoft.com/support/supportnet/default.asp The English version of this fix should have the following file attributes or later: Date Time Size File name Platform ------------------------------------------------------------- 04/28/99 05:58p 12,560 Rasfil32.dll (x86) 04/28/99 05:53p 20,752 Rasfil32.dll (Alpha) This hotfix has been posted to the following Internet location as Rasffixi.exe (x86) and Rasffixa.exe (Alpha): ftp://ftp.microsoft.com/bussys/winnt/winnt-public/fixes/usa/NT40/ hotfixes-postSP5/RAS-fix/ NOTE: If this product was already installed on your computer when you purchased it from the Original Equipment Manufacturer (OEM) and you need this fix, please call the Pay Per Incident number listed on the above Web site. If you contact Microsoft to obtain this fix, and if it is determined that you only require the fix you requested, no fee will be charged. However, if you request additional technical support, and if your no-charge technical support period has expired, or if you are not eligible for standard no-charge technical support, you may be charged a non-refundable fee. For more information about eligibility for no-charge technical support, see the following article in the Microsoft Knowledge Base: Q154871 Determining If You Are Eligible for No-Charge Technical Support STATUS ====== Microsoft has confirmed this to be a problem in the Microsoft products listed at the beginning of this article. MORE INFORMATION ================ It is important to note that the vulnerability only affects computers running the RAS client software, not RAS servers, and that the user must have permission to add or modify phonebook entries in order to initiate the attack. Permissions can be set via the phonebook?s access control list (ACL). The computers primarily at risk from this vulnerability are workstations that are configured to dial out to other computers, as servers, including Microsoft Windows NT 4.0, Terminal Server Edition, are not typically configured to act as RAS clients. This vulnerability affects only the local computer; this vulnerability does not allow a user to directly attack a remote computer. For additional security related information about Microsoft products, please visit the following Microsoft Web site: http://www.microsoft.com/security/ Additional query words: ============================================================================ THE INFORMATION PROVIDED IN THE MICROSOFT KNOWLEDGE BASE IS PROVIDED "AS IS" WITHOUT WARRANTY OF ANY KIND. MICROSOFT DISCLAIMS ALL WARRANTIES, EITHER EXPRESS OR IMPLIED, INCLUDING THE WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE. 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