MyBB Limited ACP Account Escalation to Administrator via gid=4 User Creation

Detects potential privilege escalation within the MyBB Administrative Control Panel (ACP). The rule identifies POST requests to user management modules that set a user's group ID (gid) or usergroup to 4, which typically corresponds to the administrator group in MyBB. It verifies the escalation by correlating it with a prior session that lacked administrator privileges and identifying a subsequent login event.