This indicates an attack attempt to exploit a Cross-Site Scripting Vulnerability in Jenkins build-metrics Plugin.
The vulnerability is due to insufficient sanitizing of user supplied inputs in the application. A remote attacker may be able exploit this to execute arbitrary script code within the context of the target user's browser.
Jenkins build-metrics Plugin up to and including 1.3
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.