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Mozilla Foundation Security Advisory 2010-44

Title: Characters mapped to U+FFFD in 8 bit encodings cause subsequent character to vanish
Impact: Moderate
Announced: July 20, 2010
Reporter: O. Andersen
Products: Firefox, Thunderbird

Fixed in: Firefox 3.6.7
  Thunderbird 3.1.1


Security researcher O. Andersen reported that undefined positions within various 8 bit character encodings are mapped to the sequence U+FFFD which when displayed causes the immediately following character to disappear from the text run. This could potentially contribute to XSS problems on sites which expected extra characters to be present within strings being sanitized on the server.