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Execution Security & Process Isolation

Starkite applies two complementary layers of protection to ensure that script execution and subprocess spawning remain bounded and predictable.

1. Interpreter-Level Execution Protection

When a script attempts to execute an operating system command (os.exec(), os.try_exec(), os.shell()), the Starkite interpreter intercepts the call and validates the target binary against the active capability profile:

  • Zero-Trust Default: Subprocess execution is blocked by default under the deny-all and sandbox-path profiles (exec.deny: ["*"], no_exec: true).
  • Binary Allowlisting: Under sandbox-exec and higher (or when using --sandbox-exec-allow=<bins>), binaries are checked against allowed execution rules. Passing --sandbox-exec-allow=kubectl,helm resolves the binaries across $PATH and follows symlink chains into read-only mount rules.
  • Process Permissions: All process execution (including explicit shell invocations like os.exec("sh", ["-c", "..."])) is governed uniformly by standard os.exec permission rules.
  • Identity Switching (POSIX): Executing a command under a specific user or group identity (using the userid and groupid optional keyword arguments) is a privileged operation requiring the unconfined profile or explicit os.exec(switch_identity:...) capability grant.

For instructions on defining custom execution rules and composing profiles, see the Execution Sandbox Guide.

2. OS-Level Process Sandboxing

Starkite enables OS-level sandboxing by default across native OS kernel primitives (Linux Landlock + Seccomp-BPF, macOS Seatbelt) and container runtimes (Podman, Docker, nerdctl, gVisor).

Every script runs inside explicit filesystem, network, and execution boundaries defined by its active profile:

Default Zero-Trust (deny-all profile)

  • Filesystem: Isolated. $CWD and host $HOME are not mounted. An isolated temporary scratch mount is provided at /tmp (HOME=/tmp, TMPDIR=/tmp).
  • Subprocess Execution: Blocked at both interpreter and OS kernel boundary.
  • Network: Disabled (network: none). Outbound network requests fail closed.
  • Environment: Scrubbed to minimal safe baseline (PATH, HOME, TMPDIR, LANG, TERM).

Filesystem Processing (sandbox-path profile)

  • Filesystem: $CWD mounted read/write with /tmp scratch mount.
  • Subprocess Execution: Blocked.
  • Network: Disabled (network: none).

Local Execution (sandbox-exec profile)

  • Filesystem: $CWD mounted read/write with /tmp scratch mount.
  • Subprocess Execution: Permitted for system binaries (exec.allow: ["*"]).
  • Network: Disabled (network: none).

Cloud-Native & Network Workflows (sandbox-net profile / --sandbox-net-allow)

  • Filesystem: $CWD mounted read/write, /tmp scratch mount, and automatic read-only mounts for system DNS resolvers (/etc/resolv.conf, /etc/hosts) and TLS CA certificates.
  • Subprocess Execution: Permitted for system binaries.
  • Network: Full outbound network connectivity (network: host).

For driver configuration, driver override flags (--sandbox-driver=<driver>), and programmatic Starlark module execution, see the Execution Sandbox Guide.