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TUCoPS :: Windows Net Apps :: ciacl018.htm

Microsoft "Web Server File Request Parsing"
Microsoft "Web Server File Request Parsing" Privacy and Legal Notice


L-018B: Microsoft "Web Server File Request Parsing"

(Revision to Bulletin L-018A)

November 22, 2000 18:00 GMT
PROBLEM:       Microsoft Internet Information Services 4.0/5.0 (IIS) can allow
               the execution of arbitrary code. Unicode Exploit.
PLATFORM:      Microsoft Internet Information Service 5.0. - Any System
               Microsoft Internet Information Service 4.0. - Any System
DAMAGE:        System security is compromised by the ability to remotely
               execute arbitrary software on an IIS server. A malicious user
               could compromise the integrity of data and system operation.
SOLUTION:      For all systems, apply the patches as indicated in the
               Microsoft bulletin.

VULNERABILITY The risk is LOW. There are restrictions on the type of file ASSESSMENT: requests that can be made.
[****** Start Microsoft Advisory ******] Microsoft Security Bulletin (MS00-086) -------------------------------------- Patch Available for "Web Server File Request Parsing" Vulnerability Originally posted: November 06, 2000 Updated: November 21, 2000 Summary ======= On November 06, 2000, Microsoft released the original version of this bulletin, announcing the availability of a patch that eliminates a security vulnerability in Microsoft(r) Internet Information Services 5.0. The vulnerability could enable a malicious user to run operating system commands on a web server. On November 10, 2000, we updated the bulletin to clarify the scope of the issue. On November 21, 2000, we updated it again, to discuss two newly-discovered variants of the original vulnerability. The new variants don't change the effect of exploiting the vulnerability. However, they do affect a larger number of products. The original variant affected IIS 5.0 in all cases, but only affected IIS 4.0 when a service pack prior to Windows NT 4.0 Service Pack 6a was in use. The new variants affect both IIS 4.0 and IIS 5.0 regardless of the service pack is in use. Microsoft recommends that all affected customers apply the new versions of the patches. Frequently asked questions regarding this vulnerability and the patch can be found at Issue ===== When IIS receives a valid request for an executable file, it passes the name of the requested file to the underlying operating system for processing. However, due to an implementation flaw, it is possible to create a specially-malformed file request that contains both a file name and one or more operating system commands. Upon receiving such a request, IIS would pass the entire string to the operating system, which would first process the file and then execute the commands. The ability to execute operating system commands on the web server would enable a malicious user to take virtually any action that an interactively-logged on user could take. Although this would not give the malicious user administrative control over the server, it would nevertheless enable him to cause widespread damage. He could, for instance, add, delete or change files on the server, run code that was already on the server, or upload code of his choice and run it. There are three signficant restrictions on type of file request that could be used to exploit this vulnerability: - The malicious user would need to request a .bat or .cmd file. - The file would need to exist. - The malicious user would need to have execute permissions on the file. Although these restrictions limit the scope of the vulnerability, it is important not to discount it. Many third-party software products for web servers install batch files by default. As a result, Microsoft recommends that all customers running affected versions of IIS verify whether their systems contain any .bat or .cmd files that can be executed by visitors to the site, and apply the patch immediately if this is the case. The patch for this issue also eliminates the "Web Server Directory Traversal" vulnerability discussed in Microsoft Security Bulletin MS00-078. Affected Software Versions ========================== - Microsoft Internet Information Server 4.0 - Microsoft Internet Information Services 5.0 Patch Availability ================== - Internet Information Server 4.0: - Internet Information Services 5.0: Note: The IIS 5.0 patch can be applied atop systems running either Windows 2000 Gold or Service Pack 1. It will be included in Windows 2000 Service Pack 2. Note: The IIS 4.0 patch can be applied atop systems running Windows NT 4.0 Service Pack 6a. It will be included in Windows NT 4.0 Service Pack 7. Note: Additional security patches are available at the Microsoft Download Center More Information ================ Please see the following references for more information related to this issue. - Frequently Asked Questions: Microsoft Security Bulletin MS00-086, - Microsoft Knowledge Base (KB) article Q277873, - Microsoft TechNet Security web site, Obtaining Support on this Issue =============================== This is a fully supported patch. Information on contacting Microsoft Product Support Services is available at Acknowledgments =============== Microsoft thanks NSFocus ( for reporting the original and new variants of this vulnerability to us and working with us to protect customers. Revisions ========= - November 06, 2000: Bulletin Created. - November 10, 2000: Bulletin updated to indicate that IIS 4.0 is affected when running on pre-SP6 versions of Windows NT 4.0, and to provide information on additional restrictions on the vulnerability. - November 21, 2000: Bulletin updated to discuss availability of patch that addresses new variants of 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. [****** End Microsoft Advisory ******]

CIAC wishes to acknowledge the contributions of Microsoft for the information contained in this bulletin.
CIAC services are available to DOE, DOE Contractors, and the NIH. CIAC can be contacted at:
    Voice:          +1 925-422-8193 (7 x 24)
    FAX:            +1 925-423-8002
    STU-III:        +1 925-423-2604
    World Wide Web:
                     (same machine -- either one will work)
    Anonymous FTP:
                     (same machine -- either one will work)

This document was prepared as an account of work sponsored by an agency of the United States Government. Neither the United States Government nor the University of California nor any of their employees, makes any warranty, express or implied, or assumes any legal liability or responsibility for the accuracy, completeness, or usefulness of any information, apparatus, product, or process disclosed, or represents that its use would not infringe privately owned rights. Reference herein to any specific commercial products, process, or service by trade name, trademark, manufacturer, or otherwise, does not necessarily constitute or imply its endorsement, recommendation or favoring by the United States Government or the University of California. The views and opinions of authors expressed herein do not necessarily state or reflect those of the United States Government or the University of California, and shall not be used for advertising or product endorsement purposes.
[Privacy and Legal Notice]

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