-----BEGIN PGP SIGNED MESSAGE----- Hash: SHA1 =============================================================================== >> CERT-NL, 01-Mar-2000 << >> All CERT-NL information has been moved to http://cert.surfnet.nl. Links << >> to CERT-NL information contained in this advisory are therefore outdated. << >> << >> CERT-NL also has stopped the CERT-CC-Mirror service. Due to this the << >> links to the CERT-CC mirror are obsolete. Visit the CERT-CC site for the << >> complete CERT-CC advisory texts: http://www.cert.org << =============================================================================== =============================================================================== Security Advisory CERT-NL =============================================================================== Author/Source : Nico de Koo Index : S-97-51 Distribution : World Page : 1 Classification: External Version: 1 Subject : Microsoft IIS Boundary Condition Vuln. Date : 01-Jul-97 =============================================================================== By courtesy of CIAC (The U.S. Department of Energy Computer Incident Advisory Capability we received information on a vulnerability in Microsoft Internet Information Server. CERT-NL recommends to apply the local Microsoft patch described below. ______________________________________________________________________________ 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/ CERT-NL wishes to thank CIAC for bringing this information to our attention ============================================================================== CERT-NL is the Computer Emergency Response Team for SURFnet customers. SURFnet is the Dutch network for educational, research and related institutes. CERT-NL is a member of the Forum of Incident Response and Security Teams (FIRST). All CERT-NL material is available under: http://cert.surfnet.nl/ In case of computer or network security problems please contact your local CERT/security-team or CERT-NL (if your institute is NOT a SURFnet customer please address the appropriate (local) CERT/security-team). CERT-NL is one/two hour(s) ahead of UTC (GMT) in winter/summer, i.e. UTC+0100 in winter and UTC+0200 in summer (DST). Email: cert-nl@surfnet.nl ATTENDED REGULARLY ALL DAYS Phone: +31 302 305 305 BUSINESS HOURS ONLY Fax: +31 302 305 329 BUSINESS HOURS ONLY Snailmail: SURFnet bv Attn. CERT-NL P.O. Box 19035 NL - 3501 DA UTRECHT The Netherlands NOODGEVALLEN: 06 22 92 35 64 ALTIJD BEREIKBAAR EMERGENCIES : +31 6 22 92 35 64 ATTENDED AT ALL TIMES CERT-NL'S EMERGENCY PHONENUMBER IS ONLY TO BE USED IN CASE OF EMERGENCIES: THE SURFNET HELPDESK OPERATING THE EMERGENCY NUMBER HAS A *FIXED* PROCEDURE FOR DEALING WITH YOUR ALERT AND WILL IN REGULAR CASES RELAY IT TO CERT-NL IN AN APPROPRIATE MANNER. CERT-NL WILL THEN CONTACT YOU. =============================================================================== -----BEGIN PGP SIGNATURE----- Version: PGP 6.5.1i iQA/AwUBOL6IYTSYjBqwfc9jEQKFIgCg28okAFIAJnXdZ+dyXwjmTArPoKwAoLFH YMJuB4dGC2DqoWWVbB7hx6aN =WHDJ -----END PGP SIGNATURE-----