Jenkins Script Security Plugin sandbox bypass vulnerability

The previously implemented script security sandbox protections prohibiting the use of unsafe AST transforming annotations such as @Grab (2019-01-08 fix for SECURITY-1266) could be circumvented through use of various Groovy language features:

• Use of AnnotationCollector
• Import aliasing
• Referencing annotation types using their full class name

This allowed users with Overall/Read permission, or the ability to control Jenkinsfile or sandboxed Pipeline shared library contents in SCM, to bypass the sandbox protection and execute arbitrary code on the Jenkins controller.

Using AnnotationCollector is now newly prohibited in sandboxed scripts such as Pipelines. Importing any of the annotations considered unsafe will now result in an error. During the compilation phase, both simple and full class names of prohibited annotations are rejected for element annotations.