What executors are available in shared Gitlab Runners?

I’ve read about the risks of using shared runners, specially when using the shell executor, since it’s not an isolated environment. However I’ve not seen any option in the project configuration YAML to specify a runner with a specific executor if available. It’s possible to specify Docker images so that way the build process will be executed on Docker, but I would like more fine-grained control over it (LOL, this is becoming now a suggestion).

I’m asking it because I’m worried about security and there is no point in executing a runner locally on my development machine since I could execute the “build script” directly.