search menu icon-carat-right cmu-wordmark

CERT Coordination Center

Mozilla Firefox URI filtering vulnerability

Vulnerability Note VU#783400

Original Release Date: 2007-07-26 | Last Revised: 2007-07-31


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.


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.

Note this vulnerability is only present in the Windows version of Firefox.


A remote, unauthenticated attacker may be able to execute arbitrary commands, using Firefox as an attack vector.


Mozilla has addressed this issue in Firefox

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.

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.

Vendor Information


Mozilla Affected

Updated:  July 26, 2007



Vendor Statement

We have not received a statement from the vendor.

Vendor Information

The vendor has not provided us with any further information regarding this vulnerability.


See for more details.

If you have feedback, comments, or additional information about this vulnerability, please send us email.

CVSS Metrics

Group Score Vector



This vulnerability was disclosed by Billy (BK) Rios.

This document was written by Ryan Giobbi, Jeff Gennari, and Will Dormann..

Other Information

CVE IDs: CVE-2007-3845
Severity Metric: 25.52
Date Public: 2007-07-25
Date First Published: 2007-07-26
Date Last Updated: 2007-07-31 15:21 UTC
Document Revision: 48

Sponsored by CISA.