A sandbox bypass vulnerability exists in Jenkins Script Security Plugin 1.50 and earlier in src/main/java/org/jenkinsci/plugins/scriptsecurity/sandbox/groovy/SecureGroovyScript.java that allows attackers with Overall/Read permission to provide a Groovy script to an HTTP endpoint that can result in arbitrary code execution on the Jenkins master JVM.
https://jenkins.io/security/advisory/2019-01-28/#SECURITY-1292
https://access.redhat.com/errata/RHSA-2019:0739
http://packetstormsecurity.com/files/166778/Jenkins-Remote-Code-Execution.html