This indicates an attack attempt against a Cross-Site Request-Forgery vulnerability in Jenkins Github Plugin.
The vulnerability is due to insufficient sanitization of user supplied inputs in the application. An attacker may exploit this to cause the server to perform certain actions in the context of an authorized user's session and gain unauthorized access to the affected application.
Jenkins GitHub Plugin 1.29.1 and earlier
Information Disclosure: Remote attackers can gain sensitive information from vulnerable systems.
Apply the most recent upgrade or patch from the vendor.