-----BEGIN PGP SIGNED MESSAGE----- =============================================================================== Security Advisory CERT-NL =============================================================================== Author/Source : Nico de Koo Index : S-98-07 Distribution : World Page : 1 Classification: External Version: 1 Subject : WinNT based Web Servers File Access Vuln. Date : 02-Feb-98 =============================================================================== By courtesy of CIAC (The U.S. Department of Energy Computer Incident Advisory Capability) we received information on a vulnerability in Windows NT based Web Servers File Access system. CERT-NL recommends application of the provided patches. ============================================================================== __________________________________________________________ The U.S. Department of Energy Computer Incident Advisory Capability ___ __ __ _ ___ / | /_\ / \___ __|__ / \ \___ __________________________________________________________ INFORMATION BULLETIN Windows NT based Web Servers File Access Vulnerability January 30, 1998 21:00 GMT Number I-025A ______________________________________________________________________________ PROBLEM: Some Windows NT based web servers allow access to 8.3 format filenames. This can allow unauthorized access to files via their 8.3 compatible name. PLATFORM: Microsoft Internet Information Server and Peer Web Server 4.0, Netscape FastTrack 2.x DAMAGE: By exploiting this vulnerability, remote users may gain unauthorized access to files accessed by the web server. SOLUTION: Apply the fixes listed in Section 3 of this advisory. ______________________________________________________________________________ VULNERABILITY Exploit information involving this vulnerability has been made ASSESSMENT: publicly available. ______________________________________________________________________________ Introduction ============ Windows NT file systems support filenames of up to 255 characters. For compatibility purposes, a short filename (the 8.3 filename) is usually created for each file, and can be used by older applications to access directories and files with long names. Web server file protection of directories and files in long filename (not 8.3) formats can often allow access to the short name (8.3) equivalent without restriction. Some Windows NT based Web servers base their access control check for permissions using the long filename only, and do not include the short name that may be used as an alias. For example, if there was a file named noteightdotthree.htm, and it was protected at the file level by the web server (NOT the NTFS file system itself), the access of the short name noteig~1.htm is possible. This also applies to directories. Note that NTFS level file restrictions are always applied correctly because they are not inherently tied to the long name, but to the name stored on disk, which the long name references. Some web servers allow you to set access permissions in places other than NTFS, however it is the implementation of these controls that are causing the vulnerability. The characteristics of this vulnerability also appear in IIS 3.0 and PWS 3.0, but only at the directory level. Using the long file name IIS or PWS 3.0 to protect an execute only directory inside a read-execute or read-only is not recommended. Microsoft has stated that they do not consider it a bug, but a 'bad' practice. This vulnerability may easily affect other Windows NT based WWW servers. CIAC recommends that you check with your vendor to ensure your WWW server does not exhibit this characteristic. Problem ======= This vulnerability permits attackers to gain unauthorized access to files on the Web server. It may be used to download the source code of server scripts in some configurations. If exploited it can give an intruder access to any file that the web server can access. Prevention ========== Microsoft IIS 4.0 and PWS 4.0 ============================== Microsoft has developed a hot-fix to correct the problem. CIAC has verified that the hot-fix corrects the problem described above, but has not done any regression testing. Instructions for installing it are available from Microsoft. Microsoft recommends that you update your Emergency Repair Disk before you apply the patch, as they have not regression tested the hot-fix. Microsoft's patch location: Windows NT 4.0 (CIAC recommends that Service Pack 3 is installed first): ftp://ftp.microsoft.com/bussys/IIS/iis-public/fixes/usa/security/sfn-fix/ Microsoft IIS 3.0 and PWS 3.0 ============================== Although Microsoft does not consider this a bug, CIAC recommends that you ensure directory access controls are not nested. Verify that WWW server protections are not being used to enforce protection for execute-only directories that reside in read-only or read-execute directories. Netscape FastTrack 2.x ======================= Netscape will be producing patches. _______________________________________________________________________ Thanks to: NtBugtraq Mailing List (NTBUGTRAQ@LISTSERV.NTBUGTRAQ.COM) David LeBlanc Michael Howard _______________________________________________________________________ ============================================================================== CERT-NL wishes to thank CIAC, the Computer Incident Advisory Capability 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://www.surfnet.nl/surfnet/security/cert-nl.html ftp://ftp.surfnet.nl/surfnet/net-security 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 52 87 92 82 ALTIJD BEREIKBAAR EMERGENCIES : +31 6 52 87 92 82 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: 2.6.3i Charset: cp850 iQCVAwUBNNWlcFpSTqmIRWKVAQHteAP/YJyklBZJVzKHpOpLBcYjhSDZbD+5abdv kosl4Q6xfzWirUXZOTH8vPLhjjaZ4OsZIGEMT0dmi8cIyOzc4mokwqjhjwVf7KJU 6+3zzEYypVs4fZPWzCoKD+PnhOkpe8ZV/8BSSMmSWSpyaUUgtiiXVYdqgOO91ZTt 6aEuEoSl/c0= =9kTF -----END PGP SIGNATURE-----