Microsoft Security Bulletin MS03-015: Cumulative Patch for Internet Explorer (813489)

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Title:      Cumulative Patch for Internet Explorer (813489)
Date:       23 April 2003
Software:   Microsoft (c) Internet Explorer
Impact:     Run code of the attacker's choice on a user's machine.
Max Risk:   Critical
Bulletin:   MS03-015

Microsoft encourages customers to review the Security Bulletins at: 
http://www.microsoft.com/technet/security/bulletin/MS03-015.asp
http://www.microsoft.com/security/security_bulletins/ms03-015.asp
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Issue:
======
This is a cumulative patch that includes the functionality of all 
previously released patches for Internet Explorer 5.01, 5.5 and 
6.0. In addition, it eliminates the following four newly discovered 
vulnerabilities: 


- -A buffer overrun vulnerability in URLMON.DLL that occurs because 
Internet Explorer does not correctly check the parameters of 
information being received from a web server. It could be possible 
for an attacker to exploit this vulnerability to run arbitrary code 
on a user's system. A user simply visiting an attacker's website 
could allow the attacker to exploit the vulnerability without any 
other user action.

- -A vulnerability in the Internet Explorer file upload control that 
allows input from a script to be passed to the upload control. This 
vulnerability could allow an attacker to supply a file name to the 
file upload control and automatically upload a file from the user's 
system to a web server.

- -A flaw in the way Internet Explorer handles the rendering of third 
party files. The vulnerability results because the Internet 
Explorer method for rendering third party file types does not 
properly check parameters passed to it. An attacker could create a 
specially formed URL that would inject script during the rendering 
of a third party file format and cause the script to execute in the 
security context of the user.

- -A flaw in the way modal dialogs are treated by Internet Explorer 
that occurs because an input parameter is not properly checked. 
This flaw could allow an attacker to use an injected script to 
provide access to files stored on a user's computer. Although a 
user who visited the attacker's website could allow the attacker to 
exploit the vulnerability without any other user action, an 
attacker would have no way to force the user to visit the website.

In addition to eliminating the above vulnerabilities, this patch 
also includes a fix for Internet Explorer 6.0 SP1 that corrects the 
method by which Internet Explorer displays help information in the 
local computer zone. While we are not aware of a method to exploit 
this vulnerability by itself, if it were possible to exploit it, it 
could allow an attacker to read local files on a visiting user's 
system. 

This patch also sets the Kill Bit on the Plugin.ocx ActiveX control 
which has a security vulnerability. This killbit has been set in 
order to ensure that the vulnerable control cannot be reintroduced 
onto users' systems and to ensure that users who already have the 
vulnerable control on their system are protected. This issue is 
discussed further in Microsoft Knowledge Base Article 813489. 

Like the previous Internet Explorer cumulative patch released with 
bulletin MS03-004, this cumulative patch will cause 
window.showHelp( ) to cease to function if you have not applied the 
HTML Help update. If you have installed the updated HTML Help 
control from Knowledge Base article 811830, you will still be able 
to use HTML Help functionality after applying this patch. 

Mitigating factors:
====================
There are common mitigating factors across all of the 
vulnerabilities: 


- -The attacker would have to host a web site that contained a web 
page used to exploit the particular vulnerability. 

- -By default, Outlook Express 6.0 and Outlook 2002 open HTML mails 
in the Restricted Sites Zone. In addition, Outlook 98 and 2000 open 
HTML mails in the Restricted Sites Zone if the Outlook Email 
Security Update has been installed. Customers who use any of these 
products would be at no risk from an e-mail borne attack that 
attempted to automatically exploit these vulnerabilities. The 
attacker would have no way to force users to visit a malicious web 
site. Instead, the attacker would need to lure them there, 
typically by getting them to click on a link that would take them 
to the attacker's site. 

In addition to the common factors, there are a number of individual 
mitigating factors: 

URLMON.DLL Buffer Overrun: 

- -Code that executed on the system would only run under the 
privileges of the locally logged in user. 

File Upload Control vulnerability: 

- -The attacker would have to know the explicit path and name of the 
file to be uploaded in advance.

Third Party plug-in rendering:

- -The third party plugin would have to be present on the user's 
system in order for it to be exploited

Risk Rating:
============
 - Critical

Patch Availability:
===================
 - A patch is available to fix this vulnerability. Please read the 
   Security Bulletins at

http://www.microsoft.com/technet/security/bulletin/ms03-015.asp
http://www.microsoft.com/security/security_bulletins/ms03-015.asp

   for information on obtaining this patch.


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