This indicates an attack attempt to exploit an Authentication Bypass vulnerability in WordPress WPGateway Plugin.
The vulnerability is due to a validation error in the application when handling a request. A remote unauthenticated attacker may be able to exploit this to add a malicious administrator user on the vulnerable system.
WordPress WPGateway Plugin <= 3.5
Security Bypass: Remote attackers can bypass security features of vulnerable systems.
Currently we are unaware of any vendor supplied patch or updates available for this issue.