Vulnerability Note VU#358017

Mozilla Firefox URL protocol handling vulnerability

Original Release date: 11 Jul 2007 | Last revised: 19 Jul 2007


Mozilla Firefox protocol handlers may allow remotely supplied JavaScript to execute with elevated privileges. This may allow a remote, unauthenticated attacker to execute arbitrary code on a vulnerable system.


On Microsoft Windows systems, Mozilla Firefox installs protocol handlers for Mozilla-specific protocols, such as the FirefoxURL and FirefoxHTML protocols. If Microsoft Windows encounters a URL protocol it cannot handle natively it searches the Windows registry for the appropriate protocol handler. When the correct protocol handler is found, Windows passes it the URL string. By design Windows passes the URL string to the protocol handler as it was received without performing any sanitization.

Mozilla Firefox URL protocol handlers are constructed in a way that may allow a remote attacker to execute arbitrary JavaScript with elevated (chrome) privileges. Mozilla Firefox security restrictions detect and prevent the execution of such JavaScript. However, if a remote attacker can persuade a user with Firefox installed to access a specially crafted web page using Internet Explorer, and perhaps other Windows applications, the malicious JavaScript will be executed. Reports claim this vulnerability is introduced when Firefox versions and later are installed.

Exploit code is publicly available for this vulnerability.


This vulnerability may allow a remote, unauthenticated attacker to execute JavaScript with elevated (chrome) privileges. This essentially means that the attacker can execute arbitrary code with the privileges of the user.


Mozilla has addressed this vulnerability in Firefox

Unregister the Firefox protocols

Disabling the Mozilla Firefox protocol handlers will mitigate this vulnerability. To unregister the protocol handlers, delete or rename the following registry keys:

Modifying the Windows registry may have unintended consequences and should be done with care.

Systems Affected (Learn More)

VendorStatusDate NotifiedDate Updated
MozillaAffected-18 Jul 2007
Microsoft CorporationUnknown-10 Jul 2007
If you are a vendor and your product is affected, let us know.

CVSS Metrics (Learn More)

Group Score Vector
Base N/A N/A
Temporal N/A N/A
Environmental N/A N/A



This vulnerability was publicly disclosed by Thor Larholm.

This document was written by Jeff Gennari.

Other Information

  • CVE IDs: CVE-2007-3670
  • Date Public: 10 Jul 2007
  • Date First Published: 11 Jul 2007
  • Date Last Updated: 19 Jul 2007
  • Severity Metric: 19.69
  • Document Revision: 65


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