Jenkins Git client Plugin has an OS command injection vulnerability on agents

Jenkins Git client Plugin 6.6.0 and earlier does not correctly escape the workspace directory name when it is embedded into the SSH wrapper script generated by the "Manually provided keys" Git Host Key Verification strategy on Unix agents.

This allows attackers able to control the name of a build’s working directory (e.g. through a build parameter that determines the workspace directory) to inject shell command substitution and execute arbitrary commands on the agent.

This vulnerability only has an impact when attackers can control working directories (e.g., the argument to the dir(…) Pipeline step) while not being able to control the Pipeline itself or the programs or build scripts it executes.

This vulnerability has been reported through the Jenkins Bug Bounty Program sponsored by the European Commission.
Git client Plugin 6.6.1 stores the known_hosts file used by the "Manually provided keys" Git Host Key Verification strategy in the system temporary directory, so the workspace directory name is no longer embedded in the path passed to the generated SSH wrapper script.