Microsoft Security Bulletin MS01-044

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Title:      15 August 2001 Cumulative Patch for IIS
Date:       15 August 2001
Software:   IIS 4.0 and 5.0
Impact:     Five vulnerabilities resulting in either denial of
            service or privilege elevation
Bulletin:   MS01-044

Microsoft encourages customers to review the Security Bulletin at:
http://www.microsoft.com/technet/security/bulletin/MS01-044.asp.
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Issue:
======
This patch is a cumulative patch that includes the functionality of
all security patches released to date for IIS 5.0, and all patches
released for IIS 4.0 since Windows NT(r) 4.0 Service Pack 5. 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complete listing of the patches superseded by this patch is provided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 all previously released security patches,
this patch also includes fixes for five newly discovered security
vulnerabilities affecting IIS 4.0 and 5.0: 
 - A denial of service vulnerability that could enable an attacker
   to cause the IIS 4.0 service to fail, if URL redirection has 
   been enabled. The "Code Red" worm generates traffic that can in 
   some cases exploit this vulnerability, with the result that an 
   IIS 4.0 machine that wasn't susceptible to infection via the 
   worm could nevertheless have its service disrupted by the worm. 
 - A denial of service vulnerability that could enable an attacker 
   to temporarily disrupt service on an IIS 5.0 web server. WebDAV
   doesn't correctly handle particular type of very long, invalid
   request. Such a request would cause the IIS 5.0 service to fail;
   by default, it would automatically restart. 
 - A denial of service vulnerability involving the way IIS 5.0 
   interprets content containing a particular type of invalid MIME 
   header. If an attacker placed content containing such a defect 
   onto a server and then requested it, the IIS 5.0 service would 
   be unable to serve any content until a spurious entry was removed
   from the File Type table for the site. 
 - A buffer overrun vulnerability involving the code that performs 
   server-side include (SSI) directives. An attacker who had the 
   ability to place content onto a server could include a malformed 
   SSI directive that, when the content was processed, would result
   in code of the attacker's choice running in Local System context. 
 - A privilege elevation vulnerability that results because of a flaw
   in a table that IIS 5.0 consults when determining whether a
process
   should in-process or out-of-process. IIS 5.0 contains a table that
   lists the system files that should always run in-process. However,
   the list provides the files using relative as well as absolute 
   addressing, with the result that any file whose name matched that
   of a file on the list would run in-process. 

In addition, this patch eliminates a side effect of the previous IIS
cumulative patch (discussed in the Caveats section of Microsoft
Security Bulletin MS01-026) by restoring proper functioning of
UPN-style logons via FTP and W3SVC. 

Mitigating Factors:
====================
URL Redirection denial of service: 
 - This vulnerability only affects IIS 4.0. IIS 5.0 is not
   affected. 
 - The vulnerability only occurs if URL redirection is enabled. 
 - The vulnerability does not provide any capability to compromise
   data on the server or gain administrative control over it. 

WebDAV request denial of service: 
 - The vulnerability only affects IIS 5.0. IIS 4.0 is not affected. 
 - The effect of an attack via this vulnerability would be temporary.
   The server would automatically resume normal service as soon as
   the malformed requests stopped arriving. 
 - The vulnerability does not provide an attacker with any capability
   to carry out WebDAV requests. 
 - The vulnerability does not provide any capability to compromise
   data on the server or gain administrative control over it. 

MIME header denial of service: 
 - The vulnerability only affects IIS 5.0. IIS 4.0 is not affected. 
 - In order to exploit this vulnerability, the attacker would need
   to have the ability to install content on the server. However,
   by default, unprivileged users do not have this capability, and
   best practices strongly recommend against granting it to untrusted
   users. 

SSI privilege elevation vulnerability: 
 - In order to exploit this vulnerability, the attacker would need
   to have the ability to install content on the server. However,
   by default, unprivileged users do not have this capability, and
   best practices strongly recommend against granting it to untrusted
   users. 

System file listing privilege elevation vulnerability: 
 - The vulnerability only affects IIS 5.0. IIS 4.0 is not affected. 
 - In order to exploit this vulnerability, the attacker would need
   to have the ability to install content on the server. However,
   by default, unprivileged users do not have this capability, and
   best practices strongly recommend against granting it to untrusted
   users. 

Patch Availability:
===================
 - A patch is available to fix these vulnerabilities. Please read the
   Security Bulletin
   http://www.microsoft.com/technet/security/bulletin/ms01-044.asp
   for information on obtaining this patch.

Acknowledgment:
===============
 - John Waters of Deloitte and Touche for reporting the MIME type
   denial of service vulnerability. 
 - The NSFocus Security Team (http://www.nsfocus.com) for reporting
   the SSI privilege elevation vulnerability. 
 - Oded Horovitz of Entercept(tm) Security Technologies 
  (http://www.entercept.com) for reporting the system file listing
   privilege elevation vulnerability.

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