diff --git a/.jules/sentinel.md b/.jules/sentinel.md
index 2b5d819c..aabf99a6 100644
--- a/.jules/sentinel.md
+++ b/.jules/sentinel.md
@@ -90,3 +90,8 @@
 **Vulnerability:** The `_safe_upload_filename` function used `filename.replace`, `PurePosixPath`, and `re.sub` on unbounded client input, making it vulnerable to ReDoS or CPU/memory exhaustion (DoS) when fed extremely long strings.
 **Learning:** Even fast standard library functions like `PurePosixPath` and string replacements can cause significant lag when chained on strings in the megabytes. String processing operations should always bound their inputs first if the input is untrusted and can be arbitrarily large.
 **Prevention:** Cap the length of client-provided filename strings early by slicing them (e.g. `filename = filename[-512:]`) before doing more complex string parsing or regex replacements, especially when only the basename suffix is relevant.
+
+## 2025-07-17 - Prevent DoS via TypeError in hmac.compare_digest
+**Vulnerability:** Passing strings containing non-ASCII characters directly to `hmac.compare_digest()` raises a `TypeError`, causing a 500 Internal Server Error. This can be exploited by an attacker sending malformed Authorization headers (e.g., `Bearer 漢字`) to cause a Denial of Service (DoS) on protected endpoints.
+**Learning:** `hmac.compare_digest()` in Python does not support comparing strings with non-ASCII characters; it strictly requires ASCII strings or bytes-like objects.
+**Prevention:** Always encode strings to bytes (e.g., `.encode("utf-8")`) before passing them to `hmac.compare_digest()` when handling untrusted client input.
diff --git a/src/newsdom_api/main.py b/src/newsdom_api/main.py
index 4efdad56..ca5b7599 100644
--- a/src/newsdom_api/main.py
+++ b/src/newsdom_api/main.py
@@ -133,7 +133,7 @@ def require_authorization(
         return
     expected = f"Bearer {token}"
     provided = authorization or ""
-    if not hmac.compare_digest(provided, expected):
+    if not hmac.compare_digest(provided.encode("utf-8"), expected.encode("utf-8")):
         raise HTTPException(
             status_code=401,
             detail=UNAUTHORIZED_DETAIL,