The utils.http.is_safe_url function in Django before 1.4.20, 1.5.x, 1.6.x before 1.6.11, 1.7.x before 1.7.7, and 1.8.x before 1.8c1 does not properly validate URLs, which allows remote attackers to conduct cross-site scripting (XSS) attacks via a control character in a URL, as demonstrated by a x08javascript: URL.