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install: check archive paths with is_relative_to, not a string prefix #57

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install: check archive paths with is_relative_to, not a string prefix #57

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3 changes: 2 additions & 1 deletion src/simantic/install.py
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Original file line number Diff line number Diff line change
Expand Up @@ -484,7 +484,8 @@ def _unpack_zip(payload: bytes, target: Path) -> None:
for name in archive.namelist():
# Refuse anything that would land outside the target.
dest = (incoming / name).resolve()
if not str(dest).startswith(str(incoming.resolve())):
# A path check, not a string prefix: `.x.incoming-evil` shares the prefix.
if not dest.is_relative_to(incoming.resolve()):
raise InstallError(f"archive has an unsafe path: {name}")
archive.extractall(incoming)
if target.exists():
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8 changes: 8 additions & 0 deletions tests/test_install.py
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Original file line number Diff line number Diff line change
Expand Up @@ -628,3 +628,11 @@ def test_pyrite_manifest_resolves_sim_and_rust_engine(home, monkeypatch):
assert install.resolve("sim").path == "pyrite/1.2.3/sim-osx-arm64"
monkeypatch.setattr(install, "download", lambda a, timeout=300: engine_zip({"simantic_rust.abi3.so": b"x"}))
assert install.install_rust_engine() == install.rust_engine_root() / "1.2.3"


def test_unpack_zip_refuses_a_sibling_sharing_the_prefix(tmp_path):
buf = io.BytesIO()
with zipfile.ZipFile(buf, "w") as z:
z.writestr("../.engine.incoming-evil/f", b"x")
with pytest.raises(install.InstallError, match="unsafe path"):
install._unpack_zip(buf.getvalue(), tmp_path / "engine")
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