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TUCoPS :: Windows Net Apps :: ciaci025.txt

Windows NT Based Web Servers File Access



                       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.


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.


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.


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):

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:
David LeBlanc <>
Michael Howard <>

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

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:
                        (or -- they're the same machine)
   Anonymous FTP:
                        (or -- they're the same machine)
   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
1. CIAC-BULLETIN for Advisories, highest priority - time critical
   information and Bulletins, important computer security information;
2. SPI-ANNOUNCE for official news about Security Profile Inspector
   (SPI) software updates, new features, distribution and
3. SPI-NOTES, for discussion of problems and solutions regarding the
   use of SPI products.

Our mailing lists are managed by a public domain software package
called Majordomo, which ignores E-mail header subject lines. To
subscribe (add yourself) to one of our mailing lists, send the
following request as the E-mail message body, substituting
ciac-bulletin, spi-announce OR spi-notes for list-name:

E-mail to or
        subscribe list-name
  e.g., subscribe ciac-bulletin

You will receive an acknowledgment email immediately with a confirmation
that you will need to mail back to the addresses above, as per the
instructions in the email.  This is a partial protection to make sure
you are really the one who asked to be signed up for the list in question.

If you include the word 'help' in the body of an email to the above address,
it will also send back an information file on how to subscribe/unsubscribe,
get past issues of CIAC bulletins via email, etc.

PLEASE NOTE: Many users outside of the DOE, ESnet, and NIH computing
communities receive CIAC bulletins.  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

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)

I-015: SGI IRIX Vulnerabilities (syserr and permissions programs)
I-016: SCO  /usr/bin/X11/scoterm Vulnerability
I-017: statd Buffer Overrun Vulnerability
I-018: FTP Bounce Vulnerability
I-019: Tools Generating IP Denial-of-Service Attacks
I-020: Cisco 7xx password buffer overflow - DOS
I-021: "smurf" IP Denial-of-Service Attacks
I-022: IBM AIX "routed" daemon Vulnerability
I-023: Macro Virus Update
I-024: CGI Security Hole in EWS1.1 Vulnerability

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