z_jail

Multi-layer Linux sandbox for native code execution

TLDR

Run a program inside an isolated root filesystem with seccomp enforcement

$ sudo z_jail --root=[path/to/rootfs] --seccomp-enforce -- [program] [args...]

Verify binary integrity before execution

$ sudo z_jail --root=[path/to/rootfs] --seccomp-enforce --self-hash=[blake2b_hex] -- [program]

Suppress audit JSON output

$ sudo z_jail --root=[path/to/rootfs] --quiet -- [program]

Build the ~130 KiB PIE binary from source

$ make

SYNOPSIS

z_jail --root=dir [options] -- program [args]

z_jail is a lightweight C99 sandbox for executing untrusted native binaries on Linux. It combines seven defence layers with no runtime dependencies beyond the standard C toolchain: Truthimatics verdict engine, mount/PID/net/IPC/UTS namespaces, pivot_root, capability dropping with locked securebits, PR_SET_NO_NEW_PRIVS, seccomp-BPF syscall whitelisting, and JSON audit logging with BLAKE2b content fingerprints.The parent process clones isolated namespaces, applies resource limits, pivots into --root, installs the seccomp filter, and execves the target. After the child exits, an audit record is written describing verdict, duration, sandbox settings, and executable hash.Designed for CI pipelines, CTF jails, and lightweight code evaluation, z_jail sits between minimal tools like bwrap and heavier sandboxes such as nsjail or gVisor.

PARAMETERS

--root=dir

Sandbox root directory containing the target binary and dependencies (required).

--seccomp-enforce

Enable seccomp-BPF whitelist (whitelist-v1, 15 syscalls).

--self-hash=hex

Refuse to run unless the z_jail binary matches the given BLAKE2b-256 hash.

--quiet

Suppress JSON audit output.

--verbose

Enable debug logging.

--version

Print build ID and exit.

--help

Show usage and exit.

CAVEATS

z_jail requires CAP_SYS_ADMIN (typically root) to create namespaces and pivot_root. The default seccomp whitelist allows only 15 syscalls — many programs need a custom policy or will be killed. Dynamic binaries require libraries inside --root; static binaries need only the executable. Kernel exploits and hardware side channels are outside the stated threat model.

HISTORY

Z-Jail was developed by Division-36 and released as v1 in 2026, targeting Linux kernel 5.4+ with a single make build and no external libraries.

RESOURCES

Source code · Documentation