The plugin has an option to discover PRs from forks and only trust those with admin or write access. The documentation is misleading and makes it sound as thought this will block PRs from untrusted users from being built. Instead this causes the original Jenkinsfile to be used instead of the Jenkinsfile from the fork. Not only is the phrasing of the documentation misleading, it still allows for many vectors of attack such as changing a file that the original Jenkinsfile calls.