Lunascape 5.1.3 and 5.1.4 allows remote attackers to spoof the address bar, via window.open with a relative URI, to show an arbitrary URL on the web site visited by the victim, as demonstrated by a visit to an attacker-controlled web page, which triggers a spoofed login form for the site containing that page. NOTE: a related attack was reported in which an arbitrary file: URL is shown.