Jenkins Convert To Pipeline Plugin vulnerable to command injection

Jenkins Convert To Pipeline Plugin 1.0 and earlier uses basic string concatenation to convert Freestyle projects' Build Environment, Build Steps, and Post-build Actions to the equivalent Pipeline step invocations.

This allows attackers able to configure Freestyle projects to prepare a crafted configuration that injects Pipeline script code into the (unsandboxed) Pipeline resulting from a conversion by Convert To Pipeline Plugin. If an administrator converts the Freestyle project to a Pipeline, the script will be pre-approved.