__________________________________________________________ The U.S. Department of Energy Computer Incident Advisory Capability ___ __ __ _ ___ / | /_\ / \___ __|__ / \ \___ __________________________________________________________ INFORMATION BULLETIN Microsoft "Myriad Escaped Characters" Vulnerability April 12, 2000 21:00 GMT Number K-033 ______________________________________________________________________________ PROBLEM: A vulnerability has been identified in Microsoft Internet Information Server (IIS), versions 4 & 5. Malicious users could embed a large number of escaped character sequences within a URL causing a denial of service attack. PLATFORM: Any Microsoft Internet Information Server system. DAMAGE: A Internet Information Server reading the malformed URL will suffer a denial of service attack. Attempting to interpret the URL increases the CPU load on a server. The increase in CPU load lasts only until the URL is processed by the CPU. A string of malformed URL's could make a system unusable for other processes, causing a denial of service for users. This vulnerability does not have the capability of deleting/adding files to the server or to crash the server. SOLUTION: Install the patch as provided by Microsoft. ______________________________________________________________________________ VULNERABILITY The risk is medium. No system compromise is provided by this ASSESSMENT: vulnerability, but the ability to perform a denial of service attack does exist. ______________________________________________________________________________ [ Start Microsoft Advisory ] Microsoft Security Bulletin (MS00-023) - -------------------------------------- Patch Available for "Myriad Escaped Characters" Vulnerability Originally Posted: April 12, 2000 Summary ======= Microsoft has released a patch that eliminates a security vulnerability in Microsoft(r) Internet Information Server. The vulnerability could allow a malicious user to slow a web server's response or prevent it from providing service altogether for a period of time. Frequently asked questions regarding this vulnerability and the patch can be found at http://www.microsoft.com/technet/security/bulletin/fq00-023.asp Issue ===== Special characters can be embedded in URLs by use of so-called escaped character sequences. By providing a specially-malformed URL with an extremely large number of escaped characters, a malicious user could arbitrarily increase the work factor associated with parsing the escaped characters, thereby consuming much or all of the CPU availability on the server and preventing useful work from being done. The vulnerability does not provide any capability to cause the server to fail, or to add, change or delete data on it. The slowdown would only last until the URL had been processed, at which point service would return to normal. Affected Software Versions ========================== - Microsoft Internet Information Server 4.0 - Microsoft Internet Information Server 5.0 Patch Availability ================== - Internet Information Server 4.0 http://www.microsoft.com/Downloads/Release.asp?ReleaseID=20292 - Internet Information Server 5.0 http://www.microsoft.com/Downloads/Release.asp?ReleaseID=20286 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 MS00-023, http://www.microsoft.com/technet/security/bulletin/fq00-023.asp - Microsoft Knowledge Base article Q254142 discusses this issue and will be available soon. - Microsoft TechNet Security web site, http://www.microsoft.com/technet/security/default.asp Obtaining Support on this Issue =============================== This is a fully supported patch. Information on contacting Microsoft Technical Support is available at http://support.microsoft.com/support/contact/default.asp. Acknowledgments =============== Microsoft thanks Vanja Hrustic of the Relay Group for reporting the "Myriad Escaped Character" vulnerability to us and working with us to protect customers. Revisions ========= - April 12, 2000: Bulletin Created. - ------------------------------------------------- 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. Last updated April 12, 2000 (c) 2000 Microsoft Corporation. All rights reserved. Terms of use. [ End Microsoft Advisory ] _____________________________________________________________________________ CIAC wishes to acknowledge the contributions of Microsoft Corp. for the information contained in this bulletin. _____________________________________________________________________________ CIAC, the Computer Incident Advisory Capability, is the computer security incident response team for the U.S. Department of Energy (DOE) and the emergency backup response team for the National Institutes of Health (NIH). CIAC is located at the Lawrence Livermore National Laboratory in Livermore, California. CIAC is also a founding member of FIRST, the Forum of Incident Response and Security Teams, a global organization established to foster cooperation and coordination among computer security teams worldwide. CIAC services are available to DOE, DOE contractors, and the NIH. CIAC can be contacted at: Voice: +1 925-422-8193 FAX: +1 925-423-8002 STU-III: +1 925-423-2604 E-mail: ciac@llnl.gov For emergencies and off-hour assistance, DOE, DOE contractor sites, and the NIH may contact CIAC 24-hours a day. During off hours (5PM - 8AM PST), use one of the following methods to contact CIAC: 1. Call the CIAC voice number 925-422-8193 and leave a message, or 2. Call 888-449-8369 to send a Sky Page to the CIAC duty person or 3. Send e-mail to 4498369@skytel.com, or 4. Call 800-201-9288 for the CIAC Project Leader. Previous CIAC notices, anti-virus software, and other information are available from the CIAC Computer Security Archive. 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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. 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