diff --git a/.jules/sentinel.md b/.jules/sentinel.md
index 9c9d083b..31f2868c 100644
--- a/.jules/sentinel.md
+++ b/.jules/sentinel.md
@@ -65,3 +65,8 @@
 **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.
+
+## 2024-10-13 - [DoS Risk via hmac.compare_digest with Non-ASCII Strings]
+**Vulnerability:** Sending non-ASCII characters in an HTTP header compared via `hmac.compare_digest` raises an unhandled `TypeError` ("comparing strings with non-ASCII characters is not supported"). This allows a malicious user to crash the worker process or trigger 500 errors by repeatedly sending payloads with non-ASCII characters, resulting in a Denial of Service (DoS).
+**Learning:** `hmac.compare_digest` safely compares standard ASCII strings, but strictly rejects Python strings containing non-ASCII characters.
+**Prevention:** Always encode user-provided strings (e.g., `.encode('utf-8')`) before comparing them using `hmac.compare_digest` to ensure safe byte-level comparison and prevent exception-based DoS.
diff --git a/saas_web.py b/saas_web.py
index 63265e94..5b280f05 100644
--- a/saas_web.py
+++ b/saas_web.py
@@ -114,7 +114,7 @@ async def require_api_key(request: Request, call_next):
     if configured_keys and not (request.method == "GET" and request.url.path == "/"):
         provided_key = request.headers.get("x-api-key", "")
         if not any(
-            hmac.compare_digest(provided_key, key) for key in configured_keys
+            hmac.compare_digest(provided_key.encode('utf-8'), key.encode('utf-8')) for key in configured_keys
         ):
             return JSONResponse(
                 status_code=401,
diff --git a/tests/test_saas_web.py b/tests/test_saas_web.py
index 3b57e033..305c5961 100644
--- a/tests/test_saas_web.py
+++ b/tests/test_saas_web.py
@@ -1222,6 +1222,19 @@ def test_video_content_type_accepted_by_validator(self):
             )
         )
 
+class HMACTest(unittest.TestCase):
+    def test_non_ascii_header_does_not_crash(self):
+        import os
+        from unittest.mock import patch
+        from fastapi.testclient import TestClient
+        import saas_web
+
+        client = TestClient(saas_web.app)
+        with patch.dict(os.environ, {"CODEC_CARVER_API_KEYS": "secret"}):
+            # Pass header as raw bytes to prevent test client decoding errors
+            response = client.get("/jobs/missing", headers=[(b'x-api-key', '한글키'.encode('utf-8'))])
+            self.assertEqual(response.status_code, 401)
+
 
 if __name__ == "__main__":
     unittest.main()