Operating System:

Published:

18 June 2001

Protect yourself against future threats.

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===========================================================================
             AUSCERT External Security Bulletin Redistribution

           ESB-2001.238 -- Microsoft Security Bulletin MS01-033
Unchecked Buffer in Index Server ISAPI Extension Could Enable Web Server Compromise
                               19 June 2001

===========================================================================

        AusCERT Security Bulletin Summary
        ---------------------------------

Product:                Microsoft Index Server 2.0
                        Indexing Service in Windows 2000
                        Indexing Service in Windows XP beta
Vendor:                 Microsoft
Impact:                 Execute Arbitrary Code/Commands
Access Required:        Remote

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Title:      Unchecked Buffer in Index Server ISAPI Extension Could
            Enable Web Server Compromise
Date:       18 June 2001
Software:   Index Server 2.0 and Indexing Service
Impact:     Run code of attacker's choice
Bulletin:   MS01-033

Microsoft encourages customers to review the Security Bulletin at: 
http://www.microsoft.com/technet/security/bulletin/MS01-033.asp.
- - ----------------------------------------------------------------------

Issue:
======
As part of its installation process, IIS installs several ISAPI 
extensions -- .dlls that provide extended functionality. Among these
is 
idq.dll, which is a component of Index Server (known in Windows 2000
as 
Indexing Service) and provides support for administrative scripts
(.ida 
files) and Internet Data Queries (.idq files). 

A security vulnerability results because idq.dll contains an
unchecked 
buffer in a section of code that handles input URLs. An attacker who 
could establish a web session with a server on which idq.dll is 
installed could conduct a buffer overrun attack and execute code on
the 
web server. Idq.dll runs in the System context, so exploiting the 
vulnerability would give the attacker complete control of the server 
and allow him to take any desired action on it. 

The buffer overrun occurs before any indexing functionality is 
requested. As a result, even though idq.dll is a component of Index 
Server/Indexing Service, the service would not need to be running in 
order for an attacker to exploit the vulnerability. As long as the 
script mapping for .idq or .ida files were present, and the attacker 
were able to establish a web session, he could exploit the 
vulnerability. 

Clearly, this is a serious vulnerability, and Microsoft urges all 
customers to take action immediately. Customers who cannot install
the 
patch can protect their systems by removing the script mappings for 
.idq and .ida files via the Internet Services Manager in IIS.
However, 
as discussed in detail in the FAQ, it is possible for these mappings
to 
be automatically reinstated if additional system components are added
or removed. Because of this, Microsoft recommends that all customers 
using IIS install the patch, even if the script mappings have been 
removed. 

Mitigating Factors:
====================
 - The vulnerability can only be exploited if a web session 
   can be established with an affected server. Customers 
   who have installed Index Server or Index Services but not
   IIS would not be at risk. This is the default case for 
   Windows 2000 Professional. 
 - The vulnerability cannot be exploited if the script mappings 
   for Internet Data Administration (.ida) and Internet Data 
   Query (.idq) files are not present. The procedure for 
   removing the mappings is discussed in the IIS 4.0 
   (http://www.microsoft.com/technet/security/iischk.asp) and IIS
   5.0 (http://www.microsoft.com/technet/security/iis5chk.asp)
   Security checklists, can be automatically removed via either 
   the High Security Template or the Windows 2000 Internet Server 
   Security Tool 
   (http://www.microsoft.com/technet/security/tools.asp). 
   Customers should be aware, however, that subsequently adding 
   or removing system components can cause the mapping to be 
   reinstated, as discussed in the FAQ. 
 - An attacker's ability to extend control from a compromised web
   server to other machines would depend heavily on the specific
   configuration of the network. Best practices recommend that the
   network architecture account for the inherent high-risk that 
   machines in an uncontrolled environment, like the Internet, 
   face by minimizing overall exposure though measures like DMZ's,
   operating with minimal services and isolating contact with 
   internal networks. Steps like this can limit overall exposure
   and impede an attacker's ability to broaden the scope of a 
   possible compromise. 

Patch Availability:
===================
 - A patch is available to fix this vulnerability. Please read the 
   Security Bulletin
   http://www.microsoft.com/technet/security/bulletin/ms01-033.asp
   for information on obtaining this patch.

Acknowledgment:
===============
 - eEye Digital Security (http://www.eeye.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.



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