This indicates an attack attempt to exploit an Authentication Bypass Vulnerability in Trend Micro Email Encryption Gateway.
The vulnerability is due to an error in the vulnerable application when handling a maliciously crafted HTTP request. A remote attacker may be able to exploit this to bypass authentication on vulnerable systems.
Trend Micro Email Encryption Gateway version 5.5 Build 1111 and below
System Compromise: Remote attackers can gain control of vulnerable systems.
Apply the most recent upgrade or patch from the vendor.