Open redirect vulnerability in the valid_back_url function in app/controllers/application_controller.rb in Redmine before 2.6.7, 3.0.x before 3.0.5, and 3.1.x before 3.1.1 allows remote attackers to redirect users to arbitrary web sites and conduct phishing attacks via a crafted back_url parameter, as demonstrated by "@attacker.com," a different vulnerability than CVE-2014-1985.