The HMI web server in Siemens WinCC flexible 2004 2005 2007 and 2008 before SP3; WinCC V11 (aka TIA portal) before SP2 Update 1; the TP OP MP Comfort Panels and Mobile Panels SIMATIC HMI panels; WinCC V11 Runtime Advanced; and WinCC flexible Runtime generates predictable authentication tokens for cookies which makes it easier for remote attackers to bypass authentication via a crafted cookie.