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Firefox Privacy Notice

Mozilla Foundation Security Advisory 2015-04

Cookie injection through Proxy Authenticate responses

January 13, 2015
Xiaofeng Zheng, Blue Lotus Team
Firefox, Firefox ESR, SeaMonkey, Thunderbird
Fixed in
  • Firefox 35
  • Firefox ESR 31.4
  • SeaMonkey 2.32
  • Thunderbird 31.4


Security researcher Xiaofeng Zheng of the Blue Lotus Team at Tsinghua University reported reported that a Web Proxy returning a 407 Proxy Authentication response with a Set-Cookie header could inject cookies into the originally requested domain. This could be used for session-fixation attacks. This attack only allows cookies to be written but does not allow them to be read.

In general this flaw cannot be exploited through email in the Thunderbird product, but is potentially a risk in browser or browser-like contexts.