Cumulative Patch for Internet Information Service

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 since Windows 2000 Service Pack 2 and IIS 5.1. A complete
listing of the patches superseded by this patch is provided below,
in the section titled “Additional information about this patch”.
In addition to all previously released security patches, this patch
also includes fixes for the following newly discovered security
vulnerabilities affecting IIS 4.0, 5.0 and 5.1:

– – – A Cross-Site Scripting (CSS) vulnerability affecting IIS 4.0,
5.0 and 5.1 involving the error message that’s returned to advise
that a requested URL has been redirected. An attacker who was able
to lure a user into clicking a link on his or her 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.

– A buffer overrun that results because IIS 5.0 does not correctly
validate requests for certain types of web pages known as server
side includes. An attacker would need the ability to upload a
Server-side include page to a vulnerable IIS server. If the
attacker then requested this page, a buffer overrun could result,
which would allow the attacker to execute code of their choice on
the server with user-level permissions.

– A denial of service vulnerability that results because of a flaw
in the way IIS 4.0 and 5.0 allocate memory requests when
constructing headers to be returned to a web client. An attacker
would need the ability to upload an ASP page to a vulnerable IIS
server. This ASP page, when called by the attacker, would attempt
to return an extremely large header to the calling web client.
Because IIS does not limit the amount of memory that can be used in
this case, this could case IIS to fail as a result of running out
of local memory.

– – – A denial of service vulnerability that results because IIS 5.0
and 5.1 do not correctly handle an error condition when an overly
long WebDAV request is passed to them. As a result an attacker
could cause IIS to fail – however both IIS 5.0 and 5.1 will by
default restart immediately after this failure.
There is a dependency associated with this patch – it requires the
patch from Microsoft Security Bulletin MS02-050 to be installed. If
this patch is installed and MS02-050 is not present, client side
certificates will be rejected. This functionality can be restored
by installing the MS02-050 patch.

Mitigating Factors:
====================
Redirection Cross Site Scripting:
– IIS 6.0 is not affected.
– The vulnerability 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.
– The target page must be an ASP page, which uses
Response.Redirect to redirect the client, to a new URL that is
based on the incoming URL of current request.

Server Side Include Web Pages Buffer Overrun
– IIS 4.0, IIS 5.1 and IIS 6.0 are not affected.
– The IIS Lockdown tool by default disables the ssinc.dll mapping,
which will block this attack.
– By default IIS 5.0 runs under a user account and not the system
account. Therefore an attacker who successfully exploited the
vulnerability would only gain user level permissions rather than
administrative level permissions.
– An attacker must have the ability to upload files to the IIS
Server.

ASP Headers Denial of Service
– An attacker must have the ability to upload files to the IIS
server.
– IIS 5.0 will automatically restart after failing.
– IIS 5.1 and IIS 6.0 are not affected.

WebDAV Denial of Service
– IIS 6.0 is not affected.
– IIS 5.0 and 5.1 will restart automatically after this failure.
– The IIS Lockdown tool disables WebDAV by default, which will
block this attack.

Risk Rating:
============
Important

Patch Availability:
===================
– A patch is available to fix this vulnerability. Please read the
Security Bulletins at
http://www.microsoft.com/technet/security/bulletin/ms03-018.asp
http://www.microsoft.com/security/security_bulletins/ms03-018.asp
for information on obtaining this patch.