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Mozilla Firefox fails to properly handle JavaScript onUnload events

Vulnerability Note VU#393921

Original Release Date: 2007-02-23 | Last Revised: 2007-03-07


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.

Vendor Information


Mozilla Affected

Updated:  February 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.


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This vulnerability was publicly disclosed by Michal Zalewski.

This document was written by Jeff Gennari.

Other Information

CVE IDs: CVE-2007-1092
Severity Metric: 18.36
Date Public: 2007-02-22
Date First Published: 2007-02-23
Date Last Updated: 2007-03-07 15:35 UTC
Document Revision: 30

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