Vulnerability Note VU#393921

Mozilla Firefox fails to properly handle JavaScript onUnload events

Original Release date: 23 Feb 2007 | Last revised: 07 Mar 2007


Mozilla Firefox does not properly handle JavaScript onUnload events. This vulnerability may lead to memory corruption that could allow a remote, unauthenticated attacker to execute arbitrary code on a vulnerable system.


The JavaScript onUnload event is executed when the browser exits a web page. An event handler can be installed via JavaScript to trap and process this event.

Mozilla Firefox fails to properly handle JavaScript onUnload events. Specifically, Firefox may not correctly handle freed data structures modified in the onUnload event handler, which could cause memory corruption.


By convincing a user to view a specially crafted HTML document (e.g., a web page or an HTML email message or attachment), an attacker may be able to execute arbitrary code with the privileges of the user.


Firefox has addressed this issue in Firefox version as well as Firefox See Mozilla Foundation Security Advisory 2007-08 for more information

Disable JavaScript

Disabling JavaScript will prevent exploitation of this vulnerability. For instructions on disabling JavaScript in Mozilla Firefox, refer to the Mozilla Firefox section the Securing Your Web Browser document.

Systems Affected (Learn More)

VendorStatusDate NotifiedDate Updated
MozillaAffected-26 Feb 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 Michal Zalewski.

This document was written by Jeff Gennari.

Other Information

  • CVE IDs: CVE-2007-1092
  • Date Public: 22 Feb 2007
  • Date First Published: 23 Feb 2007
  • Date Last Updated: 07 Mar 2007
  • Severity Metric: 18.36
  • Document Revision: 27


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