Vulnerability Note VU#403150

Microsoft Windows URI protocol handling vulnerability

Overview

Microsoft Windows fails to properly handle protocols specified in a URI, which could allow a remote, unauthenticated attacker to execute arbitrary commands on a vulnerable system.

I. Description

A Uniform Resource Identifier (URI) is a string of characters that can be used to identify a location, resource, or protocol. Microsoft Windows will parse a URI to determine the appropriate application that is registered to handle the protocol. More information about how Windows accomplishes this is available in Microsoft Knowledge Base article 224816. Several types of Windows applications, such as web browsers and email clients, may rely on Microsoft Windows to determine the proper application to handle a specified URI.

Internet Explorer 7 has changed how Microsoft Windows parses URIs. This has introduced a flaw that can cause Windows to incorrectly determine the appropriate handler for the protocol specified in a URI. This flaw appears to rely on having a "%" character in the URI.

Publicly available exploit code uses Mozilla Firefox as an attack vector for this vulnerability. For more information, including workarounds, please see VU#783400.

II. Impact

Microsoft Windows may incorrectly determine the appropriate application to handle a protocol. For example, a "safe" protocol such as mailto: may be incorrectly handled with an "unsafe" application, such as the Windows command interpreter. This can allow unexpected execution of arbitrary commands.

III. Solution

We are currently unaware of a practical solution to this problem.

Systems Affected

Vendor	Status	Date Updated
Microsoft Corporation	Vulnerable	27-Jul-2007

References

http://www.kb.cert.org/vuls/id/783400
http://xs-sniper.com/blog/2007/07/24/remote-command-execution-in-firefox-2005/
http://xs-sniper.com/blog/remote-command-exec-firefox-2005/
http://secunia.com/advisories/26201/
https://bugzilla.mozilla.org/show_bug.cgi?id=389580
http://support.microsoft.com/kb/224816
http://kb.mozillazine.org/Firefox_:_FAQs_:_About:config_Entries
http://en.wikipedia.org/wiki/Uniform_Resource_Identifier

Credit

This vulnerability was publicly disclosed by Billy Rios.

This document was written by Will Dormann.

Other Information

Date Public	07/25/2007
Date First Published	07/27/2007 10:49:12 AM
Date Last Updated	07/30/2007
CERT Advisory
CVE Name
Metric	18.43
Document Revision	11