This indicates an attack attempt to exploit a Cross-Site Scripting Vulnerability in Zimbra Collaboration Server.
This vulnerability is due to insufficient input validation in the Calendar feature. A remote attacker could exploit this vulnerability by enticing the target user to click on a crafted link. Successful exploitation could result in execution of script code in the security context of the target user's browser.
Zimbra Collaboration Server 8.8.x prior to 8.8.15 p30
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.