This indicates an attack attempt to exploit a Cross-Site Scripting Vulnerability in Jenkins Plot Plugin
This vulnerability is due to improper input validation for plot descriptions. A remote, authenticated attacker could exploit these vulnerabilities by sending a crafted request to the target server. Successfully exploiting these vulnerabilities could result in arbitrary code execution in the context of the victim's browser.
Jenkins Plot Plugin 2.1.10 and earlier
System Compromise: Remote attackers can gain control of vulnerable systems.
Apply the most recent upgrade or patch from the vendor.