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Mozilla Foundation Security Advisory 2010-43

Title: Same-origin bypass using canvas context
Impact: High
Announced: July 20, 2010
Reporter: Vladimir Vukicevic
Products: Firefox, Thunderbird

Fixed in: Firefox 3.6.7
  Thunderbird 3.1.1


Mozilla developer Vladimir Vukicevic reported that a canvas element can be used to read data from another site, violating the same-origin policy. The read restriction placed on a canvas element which has had cross-origin data rendered into it can be bypassed by retaining a reference to the canvas element's context and deleting the associated canvas node from the DOM.