Harden pack validator trust boundary

- reject unsafe pack IDs, path traversal, absolute paths, and separators
- require --allow-arbitrary-code for dynamic validator execution
- add --dry-run validation that does not import or execute validators
- preserve JSON/report behavior with explicit trust boundary
- add focused CLI security tests

core/cli.py

@@ -342,15 +342,60 @@ def cmd_pack_verify(args: argparse.Namespace) -> int:
     return _run(sys.executable, "-m", "language_packs", "verify", args.pack_id)
 
 
+def _safe_pack_id(pack_id: str) -> str:
+    """Reject pack IDs containing path traversal or separator characters."""
+    if not pack_id:
+        _die("pack_id is required", code=2)
+
+    path = Path(pack_id)
+
+    if path.is_absolute():
+        _die("pack_id must not be an absolute path", code=2)
+
+    if pack_id in {".", ".."}:
+        _die("pack_id must name a pack, not a relative path", code=2)
+
+    if any(part in {"", ".", ".."} for part in path.parts):
+        _die("pack_id must not contain path traversal", code=2)
+
+    if "/" in pack_id or "\\" in pack_id:
+        _die("pack_id must be a simple pack id, not a path", code=2)
+
+    return pack_id
+
+
 def cmd_pack_validate(args: argparse.Namespace) -> int:
     """Run executable source-pack validation gates."""
-    import importlib.util
-
-    pack_dir = _REPO_ROOT / "packs" / args.pack_id
+    pack_id = _safe_pack_id(args.pack_id)
+    pack_dir = _REPO_ROOT / "packs" / pack_id
     validator_path = pack_dir / "validators.py"
+
     if not validator_path.exists():
         _die(f"source-pack validator not found: {validator_path}", code=1)
-    spec = importlib.util.spec_from_file_location(f"{args.pack_id}_validators", validator_path)
+
+    if getattr(args, "dry_run", False):
+        if args.json:
+            print(json.dumps({
+                "pack_id": pack_id,
+                "validator_path": str(validator_path),
+                "would_execute": False,
+                "exists": True,
+            }, ensure_ascii=False, indent=2, sort_keys=True))
+        else:
+            print(f"dry-run: pack_id={pack_id}")
+            print(f"validator: {validator_path}")
+            print("status: validator exists, would not execute")
+        return 0
+
+    if not getattr(args, "allow_arbitrary_code", False):
+        _die(
+            "dynamic validator execution requires --allow-arbitrary-code",
+            code=2,
+        )
+
+    import importlib.util
+
+    spec = importlib.util.spec_from_file_location(f"{pack_id}_validators", validator_path)
     if spec is None or spec.loader is None:
         _die(f"cannot load source-pack validator: {validator_path}", code=1)
     module = importlib.util.module_from_spec(spec)
@@ -569,6 +614,12 @@ def build_parser() -> argparse.ArgumentParser:
     pack_validate = pack_sub.add_parser("validate", help="validate a source pack under packs/")
     pack_validate.add_argument("pack_id", help="source pack id, e.g. en, he, grc, el")
     pack_validate.add_argument("--json", action="store_true", help="emit machine-readable JSON")
+    pack_validate.add_argument("--dry-run", action="store_true", help="check validator exists without executing")
+    pack_validate.add_argument(
+        "--allow-arbitrary-code",
+        action="store_true",
+        help="permit dynamic validator execution (required to run validators)",
+    )
     pack_validate.set_defaults(func=cmd_pack_validate)
 
     rust = subparsers.add_parser(

tests/test_cli_pack_validate_security.py

@@ -0,0 +1,89 @@
+"""Security tests for the ``core pack validate`` CLI subcommand."""
+from __future__ import annotations
+
+import importlib.util
+
+import pytest
+
+from core import cli
+
+
+def test_pack_validate_requires_allow_arbitrary_code(capsys: pytest.CaptureFixture[str]) -> None:
+    with pytest.raises(SystemExit) as exc:
+        cli.main(["pack", "validate", "en"])
+
+    assert exc.value.code != 0
+    captured = capsys.readouterr()
+    assert "--allow-arbitrary-code" in captured.err
+
+
+def test_pack_validate_dry_run_does_not_execute_validator(
+    monkeypatch: pytest.MonkeyPatch,
+    capsys: pytest.CaptureFixture[str],
+) -> None:
+    def fail_import(*args: object, **kwargs: object) -> None:
+        raise AssertionError("validator should not execute during dry-run")
+
+    monkeypatch.setattr(importlib.util, "spec_from_file_location", fail_import)
+
+    rc = cli.main(["pack", "validate", "en", "--dry-run"])
+
+    assert rc == 0
+    captured = capsys.readouterr()
+    assert "dry-run" in captured.out.lower()
+
+
+@pytest.mark.parametrize(
+    "pack_id",
+    ["../foo", "/tmp/foo", "foo/bar", r"foo\bar", ".", "..", ""],
+)
+def test_pack_validate_rejects_unsafe_pack_ids(pack_id: str) -> None:
+    args = ["pack", "validate", pack_id, "--dry-run"] if pack_id else ["pack", "validate", "", "--dry-run"]
+    with pytest.raises(SystemExit) as exc:
+        cli.main(args)
+    assert exc.value.code == 2
+
+
+def test_pack_validate_rejects_path_traversal(capsys: pytest.CaptureFixture[str]) -> None:
+    with pytest.raises(SystemExit) as exc:
+        cli.main(["pack", "validate", "../foo", "--dry-run"])
+
+    assert exc.value.code == 2
+    captured = capsys.readouterr()
+    assert "path" in captured.err.lower() or "traversal" in captured.err.lower()
+
+
+def test_pack_validate_rejects_absolute_paths(capsys: pytest.CaptureFixture[str]) -> None:
+    with pytest.raises(SystemExit) as exc:
+        cli.main(["pack", "validate", "/tmp/foo", "--dry-run"])
+
+    assert exc.value.code == 2
+    captured = capsys.readouterr()
+    assert "absolute" in captured.err.lower()
+
+
+def test_pack_validate_rejects_path_separators(capsys: pytest.CaptureFixture[str]) -> None:
+    with pytest.raises(SystemExit) as exc:
+        cli.main(["pack", "validate", "foo/bar", "--dry-run"])
+
+    assert exc.value.code == 2
+    captured = capsys.readouterr()
+    assert "path" in captured.err.lower()
+
+
+def test_pack_validate_allows_known_safe_pack_with_explicit_flag() -> None:
+    rc = cli.main(["pack", "validate", "en", "--allow-arbitrary-code"])
+    assert rc in {0, 1}
+
+
+def test_pack_validate_dry_run_json(capsys: pytest.CaptureFixture[str]) -> None:
+    import json
+
+    rc = cli.main(["pack", "validate", "en", "--dry-run", "--json"])
+
+    assert rc == 0
+    captured = capsys.readouterr()
+    data = json.loads(captured.out)
+    assert data["pack_id"] == "en"
+    assert data["would_execute"] is False
+    assert data["exists"] is True