diff --git a/.jules/sentinel.md b/.jules/sentinel.md
index 9c9d083b..43aba5dc 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.
+
+## 2026-08-20 - [Sentinel: hmac.compare_digest 문자 인코딩 취약점 수정]
+**Vulnerability:** 악의적인 비-ASCII 문자가 포함된 헤더를 통해 발생하는 처리되지 않은 예외(TypeError)로 인한 서비스 거부(DoS) 취약점.
+**Learning:** Python의 `hmac.compare_digest()` 함수는 비-ASCII 문자가 포함된 문자열을 비교할 때 `TypeError`를 발생시킵니다. 웹 서버 미들웨어에서 이러한 예외를 적절히 처리하지 않으면 500 서버 오류가 발생하여 서비스 거부 공격의 경로가 될 수 있습니다.
+**Prevention:** `hmac.compare_digest()`를 호출하기 전에 항상 비교할 두 문자열을 명시적으로 바이트 형식(`.encode('utf-8')`)으로 인코딩해야 합니다.
diff --git a/saas_web.py b/saas_web.py
index 63265e94..92585502 100644
--- a/saas_web.py
+++ b/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,
diff --git a/tests/test_saas_web.py b/tests/test_saas_web.py
index 3b57e033..c99db8e1 100644
--- a/tests/test_saas_web.py
+++ b/tests/test_saas_web.py
@@ -1223,5 +1223,37 @@ def test_video_content_type_accepted_by_validator(self):
         )
 
 
+@unittest.skipUnless(
+    _HAS_FASTAPI, "fastapi not installed (optional integration dependency)"
+)
+class AuthMiddlewareTests(unittest.IsolatedAsyncioTestCase):
+    async def test_require_api_key_handles_non_ascii_gracefully(self):
+        import starlette.requests
+        import starlette.responses
+        import os
+
+        scope = {
+            'type': 'http',
+            'method': 'GET',
+            'path': '/jobs/123',
+            'headers': [(b'x-api-key', b'invalid_key_\xc3\xb8')],
+        }
+        request = starlette.requests.Request(scope)
+
+        async def mock_call_next(req):
+            return starlette.responses.Response("OK")
+
+        original_keys = os.environ.get('CODEC_CARVER_API_KEYS')
+        try:
+            os.environ['CODEC_CARVER_API_KEYS'] = 'validkey1'
+            response = await saas_web.require_api_key(request, mock_call_next)
+            self.assertEqual(response.status_code, 401)
+        finally:
+            if original_keys is not None:
+                os.environ['CODEC_CARVER_API_KEYS'] = original_keys
+            else:
+                del os.environ['CODEC_CARVER_API_KEYS']
+
+
 if __name__ == "__main__":
     unittest.main()