A flaw was found in Jenkins Pipeline. Script Security sandbox protection could be circumvented during the script compilation phase by applying AST transforming annotations such as @Grab to source code elements. This allows users with Overall/Read permission, or able to control Jenkinsfile or sandboxed Pipeline shared library contents in SCM, to bypass the sandbox protection and execute arbitrary code on the Jenkins master. All known unsafe AST transformations in Groovy are now prohibited in sandboxed scripts. Both the pipeline validation REST APIs and actual script/pipeline execution are affected. The highest threat from this vulnerability is to data confidentiality and integrity as well as system availability.