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Mozilla Foundation Security Advisory 2013-27

Title: Phishing on HTTPS connection through malicious proxy
Impact: High
Announced: February 19, 2013
Reporter: Michal Zalewski
Products: Firefox, Thunderbird, SeaMonkey

Fixed in: Firefox 19.0
  Firefox ESR 17.0.3
  Thunderbird 17.0.3
  Thunderbird ESR 17.0.3
  SeaMonkey 2.16


Google security researcher Michal Zalewski reported an issue where the browser displayed the content of a proxy's 407 response if a user canceled the proxy's authentication prompt. In this circumstance, the addressbar will continue to show the requested site's address, including HTTPS addresses that appear to be secure. This spoofing of addresses can be used for phishing attacks by fooling users into entering credentials, for example.

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