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Mozilla Foundation Security Advisory 2013-91

Title: User-defined properties on DOM proxies get the wrong "this" object
Impact: Moderate
Announced: September 17, 2013
Reporter: Boris Zbarsky
Products: Firefox, Thunderbird, Seamonkey

Fixed in: Firefox 24.0
  Firefox ESR 17.0.9
  Thunderbird 24.0
  Thunderbird ESR 17.0.9
  Seamonkey 2.21


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.