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Microsoft IIS and Exchange Malformed URL Denial of Service



Microsoft IIS and Exchange Malformed URL Denial of Service Privacy and Legal Notice

CIAC INFORMATION BULLETIN

L-054: Microsoft IIS and Exchange Malformed URL Denial of Service

March 2, 2001 19:00 GMT

PROBLEM: Malformed URL may cause a Denial of Servie in IIS 5.0 and Exchange 2000.
PLATFORM: Microsoft IIS 5.0 and Exchange 2000
DAMAGE: If a malformed URL were repeatedly sent to an affected system, a confluence of events could cause a memory allocation error that would result in the failure of the service.
SOLUTION: Install the patches as per Microsoft instructions.

VULNERABILITY
ASSESSMENT:
The risk is MEDIUM. Malformed URLs are easy to construct that would cause the Denial of Service.


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

-----------------------------------------------------------------------
Title:      Malformed URL can cause Service Failure in IIS 5.0 and
            Exchange 2000
Date:       01 March 2001
Software:   IIS 5.0 and Exchange 2000
Impact:     Denial of Service
Bulletin:   MS01-014

Microsoft encourages customers to review the Security Bulletin at:
http://www.microsoft.com/technet/security/bulletin/MS01-014.asp.
-----------------------------------------------------------------------

Issue:
======
IIS 5.0 contains a flaw affecting the way that an URL is handled if
it has a specific construction and its length is within a very narrow
range of values. If such an URL were repeatedly sent to an affected
system, a confluence of events could cause a memory allocation error
that would result in the failure of the IIS service.

Exchange 2000 is affected by the same vulnerability. To support
web-based mail clients, it introduces the ability to address items on
the store via URLs. This is done in part by using IIS 5.0, and in
part via code that is specific to Exchange 2000. Both pieces of code
contain the flaw, but the effect of exploiting the vulnerability via
either would be the same -- it could be used to cause the IIS service
to fail, but could not be used to attack the Exchange service itself.
That is, successfully attacking an Exchange server via this
vulnerability would disrupt web-based mail clients' use of the
server, but not that of MAPI-based mail clients like Outlook.

Because the flaw occurs in two different code modules, one of which
installs as part of IIS 5.0 and both of which install as part of
Exchange 2000, it is important for Exchange 2000 administrators to
install both the IIS and Exchange patches.

Mitigating Factors:
====================
 - The vulnerability would not enable the attacker to gain any
   administrative control over the server, or to alter any data
   on it.
 - The affected services automatically restart in the event of
   a failure, so an affected system would resume service almost
   immediately.
 - A successful attack against an Exchange server would only
   disrupt web-based mail clients' use of the server. The server
   would continue to be available for MAPI-based clients like
   Outlook.
 - The ISAPI involved in this vulnerability authenticates the
   user prior to servicing the request, so a properly configured
   Exchange server would be at less risk than an IIS server.

Patch Availability:
===================
 - A patch is available to fix this vulnerability. Please read the
   Security Bulletin
   http://www.microsoft.com/technet/security/bulletin/MS01-014.asp.
   for information on obtaining this patch.

Acknowledgment:
===============
 - Kevin Kotas of eSecurityOnline.com (http://eSecurityOnline.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 of Microsoft Security Bulletin ******]
_______________________________________________________________________________



CIAC wishes to acknowledge the contributions of Microsoft for the information contained in this bulletin.
CIAC services are available to DOE, DOE Contractors, and the NIH. CIAC can be contacted at:
    Voice:          +1 925-422-8193 (7 x 24)
    FAX:            +1 925-423-8002
    STU-III:        +1 925-423-2604
    E-mail:          ciac@llnl.gov
    World Wide Web:  http://www.ciac.org/
                     http://ciac.llnl.gov
                     (same machine -- either one will work)
    Anonymous FTP:   ftp.ciac.org
                     ciac.llnl.gov
                     (same machine -- either one will work)

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.
UCRL-MI-119788
[Privacy and Legal Notice]


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