🛡️ Sentinel: [CRITICAL] hmac.compare_digest의 TypeError로 인한 API 키 DoS 취약점 수정

.jules/sentinel.md

@@ -65,3 +65,7 @@
 **Vulnerability:** Path traversal in `media_shrinker.py` via unresolved `..` segments or symlink escapes before deriving conversion output paths.
 **Learning:** `Path.relative_to()` is only a lexical containment check unless both the source and root have first been resolved into canonical absolute paths. Relative paths and symlinks can otherwise bypass root-boundary assumptions.
 **Prevention:** Resolve both source and root once, reject sources outside the resolved root with a sanitized `MediaShrinkerError`, and derive `rel_source` from the resolved paths before planning outputs.
+## 2024-05-18 - API Key Authentication DoS via TypeError
+**Vulnerability:** A Denial of Service (DoS) vulnerability existed in `require_api_key` where an attacker could crash the server (HTTP 500) by providing a non-ASCII string in the `x-api-key` header, which caused a `TypeError` when compared using `hmac.compare_digest`.
+**Learning:** `hmac.compare_digest` in Python expects either ASCII-only strings or bytes. Passing a non-ASCII string directly crashes the function. Input from HTTP headers can contain non-ASCII characters and should be treated as untrusted.
+**Prevention:** Always encode user-controlled strings to bytes using `.encode('utf-8')` before using them in cryptographic or constant-time comparison functions like `hmac.compare_digest`.

saas_web.py

@@ -113,8 +113,9 @@ async def require_api_key(request: Request, call_next):
     configured_keys = get_configured_api_keys()
     if configured_keys and not (request.method == "GET" and request.url.path == "/"):
         provided_key = request.headers.get("x-api-key", "")
+        provided_key_bytes = provided_key.encode("utf-8")
         if not any(
-            hmac.compare_digest(provided_key, key) for key in configured_keys
+            hmac.compare_digest(provided_key_bytes, key.encode("utf-8")) for key in configured_keys
         ):
             return JSONResponse(
                 status_code=401,

tests/test_saas_web.py

@@ -10,6 +10,7 @@
 from types import SimpleNamespace
 
 try:
+    import starlette.requests
     from fastapi import BackgroundTasks
     from fastapi.testclient import TestClient
     from fastapi.responses import Response
@@ -675,7 +676,7 @@ def test_get_ui_includes_batch_upload_form(self):
 @unittest.skipUnless(
     _HAS_FASTAPI, "fastapi not installed (optional integration dependency)"
 )
-class TestApiKeyAuth(unittest.TestCase):
+class TestApiKeyAuth(unittest.IsolatedAsyncioTestCase):
     """Tests for the opt-in CODEC_CARVER_API_KEYS authentication middleware."""
 
     def _post_shrink(self, headers=None):
@@ -707,6 +708,27 @@ def test_missing_header_rejected_when_keys_configured(self):
         self.assertEqual(response.json(), {"error": "Invalid or missing API key"})
         self.assertNotIn("secret-key", response.text)
 
+    async def test_non_ascii_key_rejected_gracefully(self):
+        import saas_web
+        with patch.dict(os.environ, {"CODEC_CARVER_API_KEYS": "secret-key"}):
+            scope = {
+                "type": "http",
+                "method": "POST",
+                "path": "/shrink",
+                "headers": [(b"x-api-key", "non_ascii_キー".encode("utf-8"))]
+            }
+            request = starlette.requests.Request(scope)
+
+            async def mock_call_next(request):
+                return saas_web.JSONResponse(status_code=200, content={"status": "success"})
+
+            response = await saas_web.require_api_key(request, mock_call_next)
+
+        self.assertEqual(response.status_code, 401)
+        import json
+        body = json.loads(response.body)
+        self.assertEqual(body, {"error": "Invalid or missing API key"})
+
     def test_wrong_key_rejected(self):
         with patch.dict(os.environ, {"CODEC_CARVER_API_KEYS": "secret-key"}):
             response = self._post_shrink(headers={"X-API-Key": "wrong-key"})