-----BEGIN PGP SIGNED MESSAGE----- [ For Public Release ] __________________________________________________________ The U.S. Department of Energy Computer Incident Advisory Capability ___ __ __ _ ___ / | /_\ / \___ __|__ / \ \___ __________________________________________________________ INFORMATION BULLETIN Microsoft IIS Boundary Condition Vulnerability June 26, 1997 20:00 GMT Number H-77 ______________________________________________________________________________ PROBLEM: A vulnerability in Microsoft Internet Information Server (IIS) allows an outside user to cause an access violation on a server ("denial of service"). PLATFORM: Windows NT servers running Internet Information Server 2.0 or 3.0. DAMAGE: Causes an access violation (i.e., server is unresponsive). Unsaved data is lost. SOLUTION: Apply the local Microsoft patch described below. ______________________________________________________________________________ VULNERABILITY Exploit is widely available, and attack can be successfully ASSESSMENT: executed remotely. ______________________________________________________________________________ Introduction: A vulnerability in Microsoft Internet Information Server (IIS) for Windows NT 4.0 allows users to locally or remotely cause an access violation on a Web server of this configuration. The result is the server crashes, and is therefore rendered unresponsive until rebooted. To determine whether your IIS server has been successfully attacked, this access violation may be seen in Event Viewer's Application log file as a Dr. Watson entry of access violation on the INETINFO.EXE process. Problem: A Web browser sends a request such as a URL to the IIS Web server. If the request is a certain length, the sender causes an access violation on the server. This length varies from server to server, but typically ranges between 4K and 8K. Code is available which sends requests of varying sizes (lengths) to the target IIS server. Through this "trial and error", the code will eventually send the exact size request needed to render the target server unresponsive. Solution: If your server has been successfully attacked, it must be rebooted. The system operates normally once the system is rebooted. Prevention: Microsoft has developed a local patch to prevent users from successfully accomplishing this attack. This patch detects when the specific URL length is reached in IIS. CIAC recommends that you update your Emergency Repair Disk before you apply the patch, as the patch has not been regression tested and therefore may not work as described. Microsoft's patch location: Windows NT 4.0 (CIAC recommends that Service Pack 3 is installed first): ftp://ftp.microsoft.com/bussys/winnt/winnt-public/fixes/usa/nt40/hotfixes- postSP3/iis-fix/ =========================================================================== 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: +1 510-422-8193 FAX: +1 510-423-8002 STU-III: +1 510-423-2604 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), call the CIAC voice number 510-422-8193 and leave a message, or call 800-759-7243 (800-SKY-PAGE) to send a Sky Page. CIAC has two Sky Page PIN numbers, the primary PIN number, 8550070, is for the CIAC duty person, and the secondary PIN number, 8550074 is for the CIAC Project Leader. Previous CIAC notices, anti-virus software, and other information are available from the CIAC Computer Security Archive. World Wide Web: http://ciac.llnl.gov/ Anonymous FTP: ciac.llnl.gov (198.128.39.53) Modem access: +1 (510) 423-4753 (28.8K baud) +1 (510) 423-3331 (28.8K baud) CIAC has several self-subscribing mailing lists for electronic publications: 1. 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If you are not part of these communities, please contact your agency's response team to report incidents. Your agency's team will coordinate with CIAC. The Forum of Incident Response and Security Teams (FIRST) is a world-wide organization. A list of FIRST member organizations and their constituencies can be obtained via WWW at http://www.first.org/. 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. LAST 10 CIAC BULLETINS ISSUED (Previous bulletins available from CIAC) H-67: Red Hat Linux X11 Libraries Buffer Overflow H-68: Windows95 Network Password Vulnerability H-69: Vulnerability in getopt (3) H-70: Vulnerability in rpcbind H-71: Vulnerability in the at(1) program H-72: SunOS eeprom Vulnerability H-73: SunOS chkey Vulnerability H-74: Unix lpr Buffer Overrun Vulnerability H-75: Solaris Solstice AdminSuite Vulnerabilities H-76: Netscape Navigator Security Vulnerability -----BEGIN PGP SIGNATURE----- Version: 4.0 Business Edition iQCVAwUBM7LbvrnzJzdsy3QZAQE8NwP7BgQLnu/w5eRH4vBvi9DmSPoPyo5I9pts 3EP1m4emDcBoIZtKsCrdUIIXvloM3lGa7VX5z4Ru7IWBlNB+03dD/4kJtBkpEpl2 C7lwue2FfImMDfg4+M4+EMDKozbOqnLAOO2CQZe25CVkH+jXzz9BrCEO1y+Y2LaB KNrIC06BNyQ= =vFxj -----END PGP SIGNATURE-----