reject redirects to non-http(s) schemes in PipSession

news/14171.bugfix.rst

@@ -0,0 +1 @@
+Refuse to follow an HTTP redirect to a ``file:`` URL.

src/pip/_internal/network/session.py

@@ -511,6 +511,23 @@ def is_secure_origin(self, location: Link) -> bool:
 
         return False
 
+    def get_redirect_target(self, resp: Response) -> str | None:
+        target = super().get_redirect_target(resp)
+        if target is None:
+            return None
+        # Redirecting to a file:// URL doesn't make much sense and
+        # shouldn't be allowed.
+        scheme = urllib.parse.urlparse(target).scheme
+        if scheme and scheme.lower() not in ("http", "https"):
+            logger.warning(
+                "Not following redirect from %s to %s: a redirect to a non-http(s)"
+                " location is not allowed.",
+                redact_auth_from_url(resp.url),
+                redact_auth_from_url(target),
+            )
+            return None
+        return target
+
     def request(self, method: str, url: str, *args: Any, **kwargs: Any) -> Response:  # type: ignore[override]
         # Allow setting a default timeout on a session
         kwargs.setdefault("timeout", self.timeout)

tests/unit/test_network_session.py

@@ -39,6 +39,7 @@
     user_agent,
 )
 from pip._internal.utils.misc import CI_ENVIRONMENT_VARIABLES
+from pip._internal.utils.urls import path_to_url
 
 from tests.lib.output import render_to_text
 from tests.lib.server import make_mock_server, server_running
@@ -461,6 +462,49 @@ def test_unset_proxy_is_distinct_from_empty(
         assert self._resolved_proxy(session, "http://example.com") is not None
 
 
+class TestRedirectScheme:
+    @staticmethod
+    def _make_redirect_response(location: str) -> requests.Response:
+        resp = requests.Response()
+        resp.status_code = 302
+        resp.headers["Location"] = location
+        resp.url = "https://example.com/simple/foo/"
+        request = requests.PreparedRequest()
+        request.prepare(method="GET", url=resp.url, headers={})
+        resp.request = request
+        return resp
+
+    def test_get_redirect_target_refuses_file_scheme(
+        self, tmpdir: Path, caplog: pytest.LogCaptureFixture
+    ) -> None:
+        # A remote server must not be able to redirect pip into the file:// adapter
+        # and have it read a local file.
+        secret = tmpdir.joinpath("secret.txt")
+        secret.write_text("s3cr3t", encoding="utf-8")
+        resp = self._make_redirect_response(path_to_url(str(secret)))
+
+        session = PipSession()
+        with caplog.at_level(logging.WARNING):
+            assert session.get_redirect_target(resp) is None
+        assert "non-http(s) location is not allowed" in caplog.text
+
+        # Following the redirect the way requests does must not read the file.
+        followed = list(session.resolve_redirects(resp, resp.request))
+        assert followed == []
+
+    @pytest.mark.parametrize(
+        "location",
+        [
+            "https://other.example.com/elsewhere/",
+            "http://other.example.com/elsewhere/",
+            "/relative/path/",
+        ],
+    )
+    def test_get_redirect_target_allows_http_schemes(self, location: str) -> None:
+        resp = self._make_redirect_response(location)
+        assert PipSession().get_redirect_target(resp) == location
+
+
 class TestSSLContextAdapterMixinProxy:
     """Regression tests for https://github.com/pypa/pip/issues/13465