Don't allow cookies with Authorization: Bearer to bypass CSRF

Refs #2689

datasette/csrf.py

@@ -68,7 +68,10 @@ class CrossOriginProtectionMiddleware:
         # before evaluating Sec-Fetch-Site / Origin. Only "Bearer" is exempt;
         # schemes like Basic or Digest can be browser-managed and ambient.
         authorization = headers.get(b"authorization", b"").decode("latin-1")
-        if authorization:
+        cookie_header = headers.get(b"cookie")
+        # If the request also carries a Cookie header, ambient cookie auth
+        # could be in play, so do NOT treat it as exempt.
+        if authorization and not cookie_header:
             scheme = authorization.split(None, 1)[0].lower()
             if scheme == "bearer":
                 await self.app(scope, receive, send)

tests/test_csrf_middleware.py

@@ -252,6 +252,20 @@ async def test_cross_site_post_without_auth_still_blocked(bare_ds):
     assert response.status_code == 403
 
 
+@pytest.mark.asyncio
+async def test_bearer_with_cookie_does_not_bypass():
+    # Bearer + Cookie => ambient cookie auth is in play, not exempt.
+    scope = _http_scope(
+        {
+            "sec-fetch-site": "cross-site",
+            "host": "example.com",
+            "authorization": "Bearer dstok_abc",
+            "cookie": "ds_actor=anything",
+        }
+    )
+    assert await _run_middleware(scope) == ("blocked", 403)
+
+
 def test_legacy_skip_csrf_hookimpl_does_not_break_loading():
     # Plugins that still define skip_csrf must load cleanly - pluggy ignores
     # unknown hook implementations - even though the hook is no longer