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Mozilla Foundation Security Advisory 2013-73

Same-origin bypass with web workers and XMLHttpRequest

August 6, 2013
Federico Lanusse
Firefox, Firefox ESR, SeaMonkey, Thunderbird, Thunderbird ESR
Fixed in
  • Firefox 23
  • Firefox ESR 17.0.8
  • SeaMonkey 2.20
  • Thunderbird 17.0.8
  • Thunderbird ESR 17.0.8


Mozilla community member Federico Lanusse reported a mechanism where a web worker can violate same-origin policy and bypass cross-origin checks through XMLHttpRequest. This could allow for cross-site scripting (XSS) attacks by web workers.

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