Open redirect vulnerability in the redirect_back_or_default function in app/controllers/application_controller.rb in Redmine before 2.4.5 and 2.5.x before 2.5.1 allows remote attackers to redirect users to arbitrary web sites and conduct phishing attacks via a URL in the back url (back_url parameter).
https://github.com/redmine/redmine/commit/7567c3d8b21fe67e5f04e6839c1fce061600f2f3
http://www.securityfocus.com/bid/66674
http://www.redmine.org/projects/redmine/wiki/Changelog_2_4
http://www.redmine.org/projects/redmine/wiki/Changelog
http://secunia.com/advisories/57524
http://seclists.org/oss-sec/2014/q2/84