Security context is not passed with Windows massage passing. Message passing is mainly for UI and requires all of the performance it can get. Checking access f

Security context is not passed with Windows massage passing. Message passing is mainly for UI and requires all of the performance it can get. Checking access for every single message is too expensive. Just like TCP connection doesn't carry security context, you don't know what privilege the caller has. Named pipe carries security context. That's why newer Windows requires background services to close off all outside contacts except named pipe, so the service can control the access level.