SAP Kernel (RFC), KRNL32NUC, KRNL32UC and KRNL64NUC before versions 7.21, 7.21EXT, 7.22, 7.22EXT, KRNL64UC, before versions 7.21, 7.21EXT, 7.22, 7.22EXT, 7.49, 7.73 and KERNEL before versions 7.21, 7.49, 7.53, 7.73, 7.76 SAP GUI for Windows (BC-FES-GUI) before versions 7.5, 7.6, and SAP GUI for Java (BC-FES-JAV) before version 7.5, allow an attacker to prevent legitimate users from accessing a service, either by crashing or flooding the service.