Mozilla Privacy Bug

Saturday September 14th, 2002

Yesterday, ZDNet UK News reported that Mozilla has a privacy flaw involving HTTP referers. The flaw can be exploited using the onUnload JavaScript handler, which is triggered when a visitor leaves a page (for example, by clicking a link or using a bookmark). The problem is that the referer Mozilla sends is the URL of the page that the visitor is going to, not the page that he or she is exiting. This means that a site can discover where you are heading when you leave.

The security bug is present in the latest versions of Mozilla (including 1.0.1, 1.1 and 1.2 Alpha) as well as some Mozilla-based browsers, such as Netscape 6.x, Netscape 7.0, Galeon 1.2.x and Chimera 0.5. At the time of writing, no fix is available. A workaround is to disable JavaScript (Edit > Preferences > Advanced > Scripts & Plugins).

A demonstration of the exploit has been created by security researcher Sven Neuhaus, who posted details of the vulnerability to Bugtraq on Wednesday.

The bug was filed in Bugzilla as bug 145579 on Sunday 19th May, with the more serious onUnload behaviour found on Friday 7th June. The report is currently marked as "Security-Sensitive" and access to it is restricted in line with the Mozilla Security Bugs Policy.

UPDATE! Bug 145579 has now been made public.

ANOTHER UPDATE! A fix has been checked in to the trunk. A patch for the 1.0 branch will follow shortly.

YET ANOTHER UPDATE! A patch has now been checked in to the 1.0 branch.

#59 Fix is out, but how do you implement it?

by DeepFreeze3

Thursday September 19th, 2002 5:23 AM

You are replying to this message

Somebody posted a response to an article about this bug on ZDNet's web site. Here's a copy of it (Apparently, the guy was ticked off?):


Firstly, the article does a pathetic job of explaining the bug in the first place.

Secondly, it includes the single most draconian fix imaginable - sorry, folks, but disabling JavaScript is not an acceptable workaround.

Thirdly, nobody posted the one-line fix you can add to your user.js file:

user_pref("capability.policy.default.Window.onunload", "noAccess");

It's all in the Bugzilla report - which, again, nobody bothered to mention:

- <>

Do I have to do everything around here?


Now here's what I want to know:

1) Where's the user.js file?

2) How do you add the one-line fix to the user.js file? Does it involve using NotePad of WordPad? Or do you have to use something else?