Mozilla Foundation Security Advisory 2011-47
Title: Potential XSS against sites using Shift-JIS
Announced: November 8, 2011
Reporter: Yosuke Hasegawa
Products: Firefox, Thunderbird, SeaMonkey
Fixed in: Firefox 8.0
Yosuke Hasegawa reported that the Mozilla browser engine mishandled invalid sequences in the Shift-JIS encoding. When encountering an invalid pair Mozilla would turn the entire two-byte sequence into a single unknown character rather than an unknown character followed by a valid single-byte character. On some sites attackers may have been able to end their input with the first byte of a two byte sequence; when that input was later put into a page context it might cause the following delimiter (such as a double-quote) to be consumed, breaking the format of the page. Depending on the page this could potentially be used to steal data or inject script into the page.