Grabbed off the US-CERT site
Vulnerability Note VU#783400
Mozilla Firefox URI filtering vulnerability
Overview
Mozilla Firefox does not filter input when sending certain URIs to registered protocol handlers. This may allow a remote, authenticated attacker to use Firefox as a vector for executing 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. Mozilla Firefox will rely on Microsoft Windows to determine the appropriate protocol handler for certain URIs that it does not handle internally.
Firefox does not filter data passed to certain URI protocol handlers. This allows Firefox to be used as an attack vector for vulnerabilities in other applications. For example, Firefox can be used as an attack vector for the vulnerability in how Microsoft Windows itself determines the appropriate protocol handler [VU#403150]. Public exploit code for this vulnerability exists, which uses mailto, news, nntp, snews, and telnet URI handlers.
II. Impact
A remote, unauthenticated attacker may be able to execute arbitrary commands, using Firefox as an attack vector.
III. Solution
We are currently unaware of a practical solution to this problem.
Workarounds for users
Using the about:config interface, setting the following options to true will make Firefox display a prompt before sending a URI to an external handler.
network.protocol-handler.warn-external-default
network.protocol-handler.warn-external.mailto
network.protocol-handler.warn-external.news
network.protocol-handler.warn-external.nntp
network.protocol-handler.warn-external.snews
Workarounds for administrators
Blocking mailto:%00, nntp:%00, news:%00, snews:%00, telnet:%00 strings inside of HTML pages or other network streams using an application layer firewall or IPS may mitigate this vulnerability. See the xs-sniper blog for more information about known vulnerable URIs. Please note that these filters may only work for the public exploit code that is currently available. Other variations of the exploit code can bypass these restrictions.
Systems Affected
Vendor Status Date Updated
Mozilla Vulnerable 26-Jul-2007
References
http://www.kb.cert.org/vuls/id/403150
http://xs-sniper.com/blog/2007/07/24/re ... efox-2005/
http://xs-sniper.com/blog/remote-comman ... efox-2005/
http://kb.mozillazine.org/Firefox_:_FAQ ... ig_Entries
https://bugzilla.mozilla.org/show_bug.cgi?id=389580
http://support.microsoft.com/kb/224816
http://en.wikipedia.org/wiki/Uniform_Re ... Identifier
http://secunia.com/advisories/26201/
Credit
This vulnerability was disclosed by Billy (BK) Rios.
This document was written by Ryan Giobbi, Jeff Gennari, and Will Dormann..
Other Information
Date Public 25/07/2007
Date First Published 26/07/2007 16:02:37
Date Last Updated 29/07/2007
CERT Advisory
CVE Name
Metric 25.51
Document Revision 26