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On 01 APR 2010, the Mozilla Foundation announced a critical update for it’s popular Firefox web browser (we say popular, since 80% of you reading this are using it). The update corrects a critical security hole accessible from arbitrary code sent to the browser.

Mozilla Foundation Security Advisory 2010-25

Title: Re-use of freed object due to scope confusion
Impact: Critical
Announced: April 1, 2010
Reporter: Nils (MWR InfoSecurity)
Products: Firefox
Title: Re-use of freed object due to scope confusion

Fixed In: Firefox 3.6.3

Description

A memory corruption flaw leading to code execution was reported by security researcher Nils of MWR InfoSecurity during the 2010 Pwn2Own contest sponsored by TippingPoint’s Zero Day Initiative. By moving DOM nodes between documents Nils found a case where the moved node incorrectly retained its old scope. If garbage collection could be triggered at the right time then Firefox would later use this freed object.

Note: The contest winning exploit only affects Firefox 3.6 and not earlier versions. We will be patching Firefox 3.5 in an upcoming release just in case there is an alternate way of triggering the bug.

References

• https://bugzilla.mozilla.org/show_bug.cgi?id=555109
• CVE-2010-1121

This update follows another critical security hole less than 2 weeks earlier. The product can be downloaded from their website or by using the Check for Updates feature of the software (it’s a very quick update).