Mozilla developer Boris Zbarsky reported that user-defined getters on DOM proxies would incorrectly get the expando object as this. It is unlikely that this is directly exploitable but could lead to JavaScript client or add-on code making incorrect security sensitive decisions based on hacker supplied values.

In general this flaw cannot be exploited through email in the Thunderbird product because scripting is disabled, but is potentially a risk in browser or browser-like contexts.


External Reference:

http://www.mozilla.org/security/announce/2013/mfsa2013-91.html


Acknowledgements:

Red Hat would like to thank the Mozilla project for reporting this issue. Upstream acknowledges Boris Zbarsky as the original reporter.