DOCUMENT:Q221991 TITLE :Screen Saver Vulnerability Lets User Privileges be Elevated 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 Server versions 4.0, 4.0 SP1, 4.0 SP2, 4.0 SP3, 4.0 SP4 - Microsoft Windows NT Workstation 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 - Microsoft Windows NT Server version 4.0, Terminal Server Edition ------------------------------------------------------------------------------- SYMPTOMS ======== Windows NT starts a screen saver in the local system context and then immediately changes the context to match that of the logged on user. However, Windows NT does not verify that this change completed successfully. If the change fails, the screen saver is running in a privileged state which permits a specially programmed screen saver to use these privileges to elevate the security of the logged on user. RESOLUTION ========== Windows NT 4.0 -------------- A supported fix that corrects this problem is now available from Microsoft, but has not been fully regression tested and should be applied only to systems determined to be at risk of attack. Please evaluate your system's physical accessibility, network and Internet connectivity, and other factors to determine the degree of risk to your system. If your system is sufficiently at risk, Microsoft recommends you apply this fix. Otherwise, wait for the next Windows NT 4.0 service pack service pack that contain 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 ------------------------------------------------------------- 03/03/99 12:00p 247,056 Advapi32.dll (x86) 03/12/99 10:00p 188,176 Winlogon.exe (x86) 03/03/99 12:00p 404,240 Advapi32.dll (Alpha) 03/12/99 09:59p 273,680 Winlogon.exe (Alpha) This hotfix has been posted to the following Internet location as Scrnsavi.exe (x86) and Scrnsava.exe (Alpha): ftp://ftp.microsoft.com/bussys/winnt/winnt-public/fixes/usa/NT40/ hotfixes-postSP4/ScrnSav-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, a fee may be charged. This fee is refundable if it is determined that you only require the fix you requested. However, this fee is non-refundable if you request additional technical support, if your no-charge technical support period has expired, or if you are not eligible for standard no-charge technical support. 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 Windows NT 4.0 -------------- A fix for Windows NT Server 4.0, Terminal Server Edition is forthcoming. STATUS ====== Microsoft has confirmed this problem could result in some degree of security vulnerability in Windows NT 4.0 and Windows NT Server 4.0, Terminal Server Edition. MORE INFORMATION ================ For more information on this issue, please see the following Microsoft Security Bulletin at: http://www.microsoft.com/security/bulletins/MS99-008.asp For additional security related information about Microsoft products, visit the Microsoft Security Web site at: http://www.microsoft.com/security Additional query words: 4.00 Patch Available for Windows NT "Screen Saver" Vulnerability ============================================================================ 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. IN NO EVENT SHALL MICROSOFT CORPORATION OR ITS SUPPLIERS BE LIABLE FOR ANY DAMAGES WHATSOEVER INCLUDING DIRECT, INDIRECT, INCIDENTAL, CONSEQUENTIAL, LOSS OF BUSINESS PROFITS OR SPECIAL DAMAGES, EVEN IF MICROSOFT CORPORATION OR ITS SUPPLIERS HAVE BEEN ADVISED OF THE POSSIBILITY OF SUCH DAMAGES. SOME STATES DO NOT ALLOW THE EXCLUSION OR LIMITATION OF LIABILITY FOR CONSEQUENTIAL OR INCIDENTAL DAMAGES SO THE FOREGOING LIMITATION MAY NOT APPLY.