Microsoft Security Bulletin MS02-062: Cumulative Patch for Internet Information Service (Q327696)

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Title:      Cumulative Patch for Internet Information Service 
            (Q327696)
Date:       30 October 2002
Software:   Internet Information Service
Impact:     Four vulnerabilities, the most serious of which 
            could enable applications on a server to gain 
            system-level privileges.
Max Risk:   Moderate 
Bulletin:   MS02-062

Microsoft encourages customers to review the Security Bulletin at: 
http://www.microsoft.com/technet/security/bulletin/MS02-062.asp.
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Issue:
======
This patch is a cumulative patch that includes the functionality of
all security patches released for IIS 4.0 since Windows 
NT 4.0 Service Pack 6a, and all security patches released to date for
IIS 5.0 and 5.1. A complete listing of the patches 
superseded by this patch is provided below, in the section titled
"Additional information about this patch". Before applying 
the patch, system administrators should take note of the caveats
discussed in the same section. 

In addition to including previously released security patches, this
patch also includes fixes for the following newly 
discovered security vulnerabilities affecting IIS 4.0, 5.0 and/or
5.1: 
 - A privilege elevation vulnerability affecting the way ISAPIs
   are launched when an IIS 4.0, 5.0 or 5.1 server is configured 
   to run them out of process. By design, the hosting process 
   (dllhost.exe) should run only in the security context of the 
   IWAM_computername account; however, it can actually be made to 
   acquire LocalSystem privileges under certain circumstances, 
   thereby enabling an ISAPI to do likewise. 
 - A denial of service vulnerability that results because of a flaw
   in the way IIS 5.0 and 5.1 allocate memory for WebDAV requests. 
   If a WebDAV request were malformed in a particular way, IIS would
   allocate an extremely large amount of memory on the server. By 
   sending several such requests, an attacker could cause the server
   to fail. 
 - A vulnerability involving the operation of the script source 
   access permission in IIS 5.0. This permission operates in 
   addition to the normal read/write permissions for a virtual 
   directory, and regulates whether scripts, .ASP files and 
   executable file types can be uploaded to a write-enabled virtual 
   directory. A typographical error in the table that defines the 
   file types subject to this permission has the effect of omitting
   .COM files from the list of files subject to the permission. As a 
   result, a user would need only write access to upload such a file.
 - A pair of Cross-Site Scripting (CSS) vulnerabilities affecting 
   IIS 4.0, 5.0 and 5.1, and involving administrative web page. Each
   of these vulnerabilities have the same scope and effect: an 
   attacker who was able to lure a user into clicking a link on his 
   web site could relay a request containing script to a third-party 
   web site running IIS, thereby causing the third-party site's
   response (still including the script) to be sent to the user. 
   The script would then render using the security settings of 
   the third-party site rather than the attacker's. 

In addition, the patch causes 5.0 and 5.1 to change how frequently
the socket backlog list - which, when all connections on a 
server are allocated, holds the list of pending connection requests -
is purged. The patch changes IIS to purge the list more 
frequently in order to make it more resilient to flooding attacks.
The backlog monitoring feature is not present in IIS 4.0.

Mitigating Factors:
====================
Out of Process Privilege Elevation: 
 - This vulnerability could only be exploited by an attacker 
   who already had the ability to load and execute applications
   on an affected web server. Normal security practices recommend
   that untrusted users not be allowed to load applications onto 
   a server, and that even trusted users' applications be 
   scrutinized before allowing them to be loaded. 

WebDAV Denial of Service: 
 - The vulnerability does not affect IIS 4.0, as WebDAV is not 
   supported in this version of IIS. 
 - The vulnerability could only be exploited if the server allowed
   WebDAV requests to be levied on it. The IIS Lockdown Tool 
  
(http://www.microsoft.com/technet/security/tools/tools/locktool.asp),
   if deployed in its default configuration, disables such requests. 

Script Source Access Vulnerability: 
 - The vulnerability could only be exploited if the administrator 
   had granted all users write and execute permissions to one or 
   more virtual directories on the server. Default configurations of 
   IIS would be at no risk from this vulnerability. 
 - The vulnerability does not affect IIS 4.0, as WebDAV is not 
   supported in this version of IIS. 
 - The vulnerability could only be exploited if the server allowed 
   WebDAV requests to be levied on it. The IIS Lockdown Tool, if 
   deployed in its default configuration, disables such requests. 

Cross-site Scripting in IIS Administrative Pages: 
 - The vulnerabilities could only be exploited if the attacker 
   could entice another user into visiting a web page and clicking
   a link on it, or opening an HTML mail. 
 - By default, the pages containing the vulnerability are restricted 
   to local IP address. As a result, the vulnerability could only
   be exploited if the client itself were running IIS.

Aggregate Risk Rating:
============
 - Internet systems: Moderate
 - Intranet systems: Moderate
 - Client systems: Low

Patch Availability:
===================
 - A patch is available to fix this vulnerability. Please read the 
   Security Bulletin at
   http://www.microsoft.com/technet/security/bulletin/ms02-062.asp
   for information on obtaining this patch.

Acknowledgment:
===============
 - Li0n of A3 Security Consulting Co., Ltd. (http://www.a3sc.co.kr)
   for reporting the Out of process privilege elevation 
   vulnerability. 
 - Mark Litchfield of Next Generation Security Software Ltd. 
   (http://www.nextgenss.com) for reporting the WebDAV denial 
   of service vulnerability. 
 - Luciano Martins of Deloitte & Touche Argentina 
   (http://www.deloitte.com.ar) for recommending the change in the
   socket backlog list purge rate.

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