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Category:   Application (Web Server/CGI)  >   Microsoft Internet Information Server (IIS) Web Server Vendors:   Microsoft
Microsoft IIS Web Server Contains Multiple Vulnerabilities That Allow Local Users to Gain System Privileges and Allow Remote Users to Cause the Web Server to Crash
SecurityTracker Alert ID:  1002212
SecurityTracker URL:  http://securitytracker.com/id/1002212
CVE Reference:   CVE-2001-0555, CVE-2001-0508, CVE-2001-0554, CVE-2001-0506, CVE-2001-0507   (Links to External Site)
Updated:  Dec 1 2003
Original Entry Date:  Aug 17 2001
Impact:   Denial of service via network, Execution of arbitrary code via local system, Root access via local system
Fix Available:  Yes  Vendor Confirmed:  Yes  
Version(s): IIS 4.0 and 5.0
Description:   Microsoft announced that five new vulnerabilities have been discovered in its Internet Information Server (IIS) web server 4.0 and 5.0 releases. These vulnerabilities allow remote users to disrupt the web server and allow local users to gain system level privileges on the server.

1) In IIS 4.0 only and with URL redirection enabled, a remote user can cause the web service to crash by sending certain malformed packets. The vendor notes that the "Code Red" worm attack may trigger this vulnerability in some cases. This flaw can be triggered when a URL redirection request's actual length is different from the length specified in the request.

2) In IIS 5.0 only, a remote user can temporarily disrupt service by sending certain long, invalid URL requests. This is reportedly due to a flaw in the way that WebDAV processes these requests. If this vulnerability is triggered, the web service would crash and restart.

3) In IIS 5.0 only, a remote user can cause the web service to crash by requesting a particular type of file that contains an invalid MIME header. This would require a local user (or user with access to the server) to first place the malicious content on the server. The vendor reports that the web service would be unable to serve any content until a certain spurious entry is removed from the File Type table for the web site.

4) The code that peforms server-side include (SSI) directives reportedly contains a buffer overflow. A local user or a user with access to the web server could place malicious content on the server that contains a malformed SSI directive. Then, a remote user could request the content, causing arbitrary code (supplied by the local user) to be executed in Local System context. This allows a remote user to gain elevated privileges.

5) In IIS 5.0 only, a local user can exploit the relative path listings in a table that lists the system files that should always run in-process. IIS 5.0 consults this table when determining whether a process should run in-process or out-of-process. A local user can cause IIS 5.0 to execute arbitrary code, giving the local user elevated privileges.

Impact:   These vulnerabilities allow remote users to cause denial of service conditions and allow local users to gain system privileges and take full control of the server.
Solution:   Microsoft has released 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:

Microsoft IIS 4.0:
http://www.microsoft.com/Downloads/Release.asp?ReleaseID=32061

The IIS 4.0 patch can be installed on systems running Windows NT 4.0 Service Pack 5 or Service Pack 6a.

Microsoft IIS 5.0:

http://www.microsoft.com/Downloads/Release.asp?ReleaseID=32011

The IIS 5.0 patch can be installed on systems running Windows 2000 Service Pack 1 and Service Pack 2.

The vendor reportedly plans to include the fix for these issues in Windows 2000 Service Pack 3.

This patch superceeds several previous Microsoft patches. In addition, there are several caveats listed. Please read the Vendor URL for additional information.

Vendor URL:  www.microsoft.com/technet/security/bulletin/MS01-044.asp (Links to External Site)
Cause:   Boundary error, Exception handling error, Resource error
Underlying OS:  Windows (NT), Windows (2000)

Message History:   This archive entry has one or more follow-up message(s) listed below.
(More Information is Provided on the ssinc.dll Flaw) Re: Microsoft IIS Web Server Contains Multiple Vulnerabilities That Allow Local Users to Gain System Privileges and Allow Remote Users to Cause the Web Server to Crash
NSFocus provides more information on one of the vulnerabilities.



 Source Message Contents

Subject:  Microsoft Security Bulletin MS01-044


The following is a Security  Bulletin from the Microsoft Product Security
Notification Service.

Please do not  reply to this message,  as it was sent  from an unattended
mailbox.
                    ********************************

 
-----BEGIN PGP SIGNED MESSAGE-----

- ----------------------------------------------------------------------
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.
- ----------------------------------------------------------------------

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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"AS IS" WITHOUT WARRANTY OF ANY KIND. MICROSOFT DISCLAIMS ALL
WARRANTIES, EITHER EXPRESS OR IMPLIED, INCLUDING THE WARRANTIES OF
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