This indicates an attack attempt to exploit a Cross-Site Scripting vulnerability in Trend Micro Email Encryption Gateway.
The vulnerability is due to insufficient sanitizing of user supplied inputs when the vulnerable software handles a maliciously crafted HTTP request. A remote attacker may be able to exploit this to execute arbitrary script code within the context of the user's browser, via a crafted HTTP request.
Trend Micro Email Encryption Gateway version 5.5 Build 1111 and below
System Compromise: Remote attackers can execute arbitrary script code within the context of the target user's browser.
Apply the most recent upgrade or patch from the vendor.