The protocolIs function in platform/KURLGoogle.cpp in WebCore in WebKit before r55822, as used in Google Chrome before 4.1.249.1036 and Flock Browser 3.x before 3.0.0.4112, does not properly handle whitespace at the beginning of a URL, which allows remote attackers to conduct cross-site scripting (XSS) attacks via a crafted javascript: URL, as demonstrated by a \x00javascript:alert sequence.