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TUCoPS :: Windows Net Apps :: ciacl073.txt

MS ISA web proxy DoS




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             __________________________________________________________

                       The U.S. Department of Energy
                     Computer Incident Advisory Center
                           ___  __ __    _     ___
                          /       |     /_\   /
                          \___  __|__  /   \  \___
             __________________________________________________________

                             INFORMATION BULLETIN

               Microsoft ISA Web Proxy Service Denial of Service
                         [Microsoft Bulletin MS01-021]

April 20, 2001 00:00 GMT                                          Number L-073
______________________________________________________________________________
PROBLEM:       The ISA server web proxy service does not correctly handle web 
               requests that contain a particular type of malformed argument. 
               Processing such a request would cause the web proxy service to 
               fail, blocking all incoming and outgoing requests until the 
               service is restarted. 
PLATFORM:      Microsoft ISA Server 2000 
DAMAGE:        Crashing the web proxy service would block all incoming and 
               outgoing requests creating a denial of service condition. 
SOLUTION:      Apply the patch as shown in Microsoft Security Bulletin 
               MS01-021. 
               http://www.microsoft.com/technet/security/bulletin/MS01-021.asp. 
______________________________________________________________________________
VULNERABILITY  The risk is LOW. Restarting the web proxy service clears the 
ASSESSMENT:    blockage. The vulnerability cannot allow an intruder to breach 
               security. The blockage does not disrupt any other services on 
               the ISA server. 
______________________________________________________________________________

   [***** Start Microsoft Security Bulletin *****]

- - -----------------------------------------------------------------------
Title:      Invalid Web Request Can Cause Access Violation in ISA 
            Server Web Proxy Service
Date:       16 April 2001
Software:   ISA Server 2000
Impact:     Denial of service
Bulletin:   MS01-021

Microsoft encourages customers to review the Security Bulletin 
at: http://www.microsoft.com/technet/security/bulletin/MS01-021.asp.
- - -----------------------------------------------------------------------

Issue:
======
The ISA Server Web Proxy service does not correctly handle web 
requests that contain a particular type of malformed argument. 
Processing such a request would result in an access violation, 
which would cause the Web Proxy service to fail. This would disrupt 
all ingoing and outgoing web proxy requests until the service was 
restarted. 

Mitigating Factors:
====================
 - The vulnerability could be exploited from the Internet only 
   if the Web Publishing feature were enabled. By default, 
   this feature is disabled. 
 - The vulnerability would not enable an attacker to breach the 
   security of the firewall - that is, it would not enable the 
   attacker to access protected resources or bypass the firewall. 
   It would only enable the attacker to deny legitimate service 
   to other users. 
 - The vulnerability would only allow the Web Proxy service to 
   be disrupted. Other ISA services would continue functioning 
   normally. 

Patch Availability:
===================
 - A patch is available to fix this vulnerability. Please read 
   Security Bulletin
   http://www.microsoft.com/technet/security/bulletin/ms01-021.asp
   for information on obtaining this patch.

Acknowledgment:
===============
 - Dr. Richard Reiner, Graham Wiseman, Matthew Siemens, and 
   Kent Nicolson of FSC Internet Corp. / SecureXpert Labs 
  (http://www.fscinternet.com / http://www.securexpert.com) 

- - ----------------------------------------------------------------------

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.

   [***** End Microsoft Security Bulletin *****]

______________________________________________________________________________

CIAC wishes to acknowledge the contributions of Microsoft 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 (7x24)
    FAX:      +1 925-423-8002
    STU-III:  +1 925-423-2604
    E-mail:   ciac@ciac.org

Previous CIAC notices, anti-virus software, and other information are
available from the CIAC Computer Security Archive.

   World Wide Web:      http://www.ciac.org/
                        (or http://ciac.llnl.gov -- they're the same machine)
   Anonymous FTP:       ftp.ciac.org
                        (or ciac.llnl.gov -- they're the same machine)

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 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)

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L-070: FTP Filename Expansion Vulnerability
L-071: Various Vendors' Network Time Protocol (NTP) Vulnerability
L-072: Cisco Catalyst 5000 Series 802.1x Vulnerability



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