DOCUMENT:Q218473 TITLE :Restricting Changes to Base System Objects 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 3.5, 3.51, 4.0, 4.0 SP1, 4.0 SP2, 4.0 SP3, 4.0 SP4 - Microsoft Windows NT Server versions 3.5, 3.51, 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 versions 4.0, Terminal Server Edition ------------------------------------------------------------------------------- IMPORTANT: This article contains information about editing the registry. Before you edit the registry, make sure you understand how to restore it if a problem occurs. For information about how to do this, view the "Restoring the Registry" Help topic in Regedit.exe or the "Restoring a Registry Key" Help topic in Regedt32.exe. SYMPTOMS ======== If a non-administrative level user logs on interactively to your computer, it may be possible for the user to gain local administrative privileges. A user may load a non-Microsoft dynamic-link library (DLL) into memory having the same name as a core operating system DLL and then programmatically change the entry in the KnownDLLs list to point to the malicious copy. Programs then requesting the system DLL will instead be directed to the malicious copy. When called by a program with sufficiently high security privileges, it may be possible to bypass typical security related activities such as adding a user to the Local Administrators group. A remote user may also submit an arbitrary program to run on your computer to exploit this vulnerability. CAUSE ===== In Windows NT, core operating system DLLs are kept in virtual memory and shared between programs. This prevents redundant copies of the DLL in memory, and improves memory usage and system performance. When a program calls a function provided by one of these DLLs, the operating system refers to a data structure called the KnownDLLs list to determine the location of the DLL in virtual memory. The Windows NT security architecture protects in-memory DLLs against modification, but by default it allows all users to read/write access to the KnownDLLs list. This vulnerability is only local to the computer where a malicious user is logged on interactively. For example, a workstation user could exploit this vulnerability to become a local administrator, but cannot use it directly to become a domain administrator. This restricts the impact of this issue as non-administrative users are not granted the ability to interactively log on to servers (following recommended Microsoft security practices). 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 ------------------------------------------------------------- 02/24/99 07:45p 40,208 Smss.exe (x86) 02/24/99 07:44p 62,736 Smss.exe (Alpha) This hotfix has been posted to the following Internet location as Smssfixi.exe (x86) and Smssfixa.exe (Alpha): ftp://ftp.microsoft.com/bussys/winnt/winnt-public/fixes/usa/NT40/ hotfixes-postSP4/Smss-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 Server 4.0, Terminal Server Edition ---------------------------------------------- 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 Server 4.0, Terminal Server Edition 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 ------------------------------------------------------------- 02/26/99 11:40p 44,816 Smss.exe (x86) 02/26/99 11:54p 72,464 Smss.exe (Alpha) This hotfix has been posted to the following Internet location as Smssfixi.exe (x86) and Smssfixa.exe (Alpha): ftp://ftp.microsoft.com/bussys/winnt/winnt-public/fixes/usa/NT40TSE/ hotfixes-postSP3/Smss-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 WORKAROUND WARNING: Using Registry Editor incorrectly can cause serious problems that may require you to reinstall your operating system. Microsoft cannot guarantee that problems resulting from the incorrect use of Registry Editor can be solved. Use Registry Editor at your own risk. For information about how to edit the registry, view the "Changing Keys And Values" Help topic in Registry Editor (Regedit.exe) or the "Add and Delete Information in the Registry" and "Edit Registry Data" Help topics in Regedt32.exe. Note that you should back up the registry before you edit it. If you are running Windows NT, you should also update your Emergency Repair Disk (ERD). To work around this issue, enable stronger protection on system base objects such as the KnownDLLs list by doing the following: 1. Click Start, click Run, type "regedt32" (without the quotation marks), and then click OK. 2. On the Windows menu, click "HKEY_LOCAL_ MACHINE on Local Machine". 3. Double-click the \System\CurrentControlSet\Control\Session Manager folder. 4. On the Edit menu, click Add Value, type "ProtectionMode" (without the quotation marks), click REG_DWORD in the Data Type box, and then click OK. 5. Type "1" (without the quotation marks) in the Data box, and then click OK. 6. Quit Registry Editor, and then restart the computer. STATUS ====== Microsoft has confirmed this problem could result in some degree of security vulnerability in the Microsoft products listed at the beginning of this article. MORE INFORMATION ================ For additional security related information about Microsoft products, please visit the Web site at: 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. 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.