A sandbox bypass vulnerability exists in Pipeline: Groovy Plugin 2.61 and earlier in src/main/java/org/jenkinsci/plugins/workflow/cps/CpsFlowDefinition.java, src/main/java/org/jenkinsci/plugins/workflow/cps/CpsGroovyShellFactory.java that allows attackers with Overall/Read permission to provide a pipeline script to an HTTP endpoint that can result in arbitrary code execution on the Jenkins master JVM.
A sandbox bypass vulnerability exists in Pipeline: Declarative Plugin 1.3.3 and earlier in pipeline-model-definition/src/main/groovy/org/jenkinsci/plugins/pipeline/modeldefinition/parser/Converter.groovy that allows attackers with Overall/Read permission to provide a pipeline script to an HTTP endpoint that can result in arbitrary code execution on the Jenkins master JVM.
A sandbox bypass vulnerability exists in Pipeline: Groovy Plugin 2.59 and earlier in groovy-sandbox/src/main/java/org/kohsuke/groovy/sandbox/SandboxTransformer.java, groovy-cps/lib/src/main/java/com/cloudbees/groovy/cps/SandboxCpsTransformer.java that allows attackers with Job/Configure permission, or unauthorized attackers with SCM commit privileges and corresponding pipelines based on Jenkinsfiles set up in Jenkins, to execute arbitrary code on the Jenkins master JVM
Builds in Jenkins are associated with an authentication that controls the permissions that the build has to interact with other elements in Jenkins. The Pipeline: Build Step Plugin did not check the build authentication it was running as and allowed triggering any other project in Jenkins.
Arbitrary code execution due to incomplete sandbox protection: Constructors, instance variable initializers, and instance initializers in Pipeline scripts were not subject to sandbox protection, and could therefore execute arbitrary code. This could be exploited e.g. by regular Jenkins users with the permission to configure Pipelines in Jenkins, or by trusted committers to repositories containing Jenkinsfiles.