The django.util.http.is_safe_url function in Django before 1.4.18, 1.6.x before 1.6.10, and 1.7.x before 1.7.3 does not properly handle leading whitespaces, which allows remote attackers to conduct cross-site scripting (XSS) attacks via a crafted URL, related to redirect URLs, as demonstrated by a "\njavascript:" URL.