A vulnerability has been reported in Mozilla and Mozilla Firefox, allowing malicious websites to spoof the user interface.

The problem is that Mozilla and Mozilla Firefox don't restrict websites from including arbitrary, remote XUL (XML User Interface Language) files. This can be exploited to "hijack" most of the user interface (including tool bars, SSL certificate dialogs, address bar and more), thereby controlling almost anything the user sees.

The Mozilla user interface is built using XUL files.

A PoC (Proof of Concept) exploit for Mozilla Firefox has been published. The PoC spoofs a SSL secured PayPal website.

This has been confirmed using Mozilla 1.7 for Linux, Mozilla Firefox 0.9.1 for Linux, Mozilla 1.7.1 for Windows and Mozilla Firefox 0.9.2 for Windows. Prior versions may also be affected.

NOTE: This issue appears to be the same as Mozilla Bug 244965.

Solution
The vulnerability has been partly fixed in Mozilla Firefox 1.0PR so that the status bar always is visible. A final solution will be added in an upcoming version.
Further details available to Secunia VIM customers

Provided and/or discovered by
Reported in Mozilla Firefox by:
Jeff Smith (also created a PoC)

Reported in Mozilla by:
James Ross

Changelog
Further details available to Secunia VIM customers

Original Advisory
Original Advisory and Proof of Concept:
http://www.nd.edu/~jsmith30/xul/test/spoof.html

Other references
Further details available to Secunia VIM customers

Deep Links
Links available to Secunia VIM customers