Fission builder accepts arbitrary buildcmd strings from Environment.spec.builder.command, allowing the builder pod to invoke arbitrary executables

Fission is an open-source, Kubernetes-native serverless framework that simplifies the deployment of functions and applications on Kubernetes. Prior to version 1.23.0, before the round-1 security sweep, pkg/builder/builder.go passed Environment.spec.builder.command directly into exec.Command(...) after a strings.Fields split, with no validation of the executable path or its arguments. A user who could create or update Environment CRDs in a namespace observed by the buildermgr could thereby point the builder pod at any executable inside the builder image (e.g. /bin/sh -c '...') and execute arbitrary code in the builder pod context. This issue has been patched in version 1.23.0.