From 0b3b6b7c98bcc57c2b35a44dd7df5211de7c5baf Mon Sep 17 00:00:00 2001
From: "google-labs-jules[bot]"
 <161369871+google-labs-jules[bot]@users.noreply.github.com>
Date: Sat, 5 Sep 2026 23:51:29 +0000
Subject: [PATCH] =?UTF-8?q?=F0=9F=9B=A1=EF=B8=8F=20Sentinel:=20Fix=20swall?=
 =?UTF-8?q?owed=20exception=20stack=20traces?=
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The `unhandled_exception_handler` was correctly obscuring stack traces from
being sent to clients (returning a generic 500), but it neglected to log the
exceptions server-side, resulting in completely swallowed tracebacks and
blindspots for operators. Fixed by adding `log.error` with `exc_info`.

Co-authored-by: n24q02m <135627235+n24q02m@users.noreply.github.com>
---
 .jules/sentinel.md        | 5 +++++
 src/tacet/serve/server.py | 1 +
 2 files changed, 6 insertions(+)

diff --git a/.jules/sentinel.md b/.jules/sentinel.md
index 80d5d5e..d79bedd 100644
--- a/.jules/sentinel.md
+++ b/.jules/sentinel.md
@@ -35,3 +35,8 @@
 **Vulnerability:** The FastAPI application was missing the `Referrer-Policy` security header, which could leak sensitive path information or query parameters via the `Referer` header to external sites when navigating away from the application.
 **Learning:** Even when setting strict `Content-Security-Policy` and `X-Frame-Options`, `Referrer-Policy` is needed to prevent cross-origin information leakage on outbound requests.
 **Prevention:** Always include `Referrer-Policy: no-referrer` in the global security headers middleware to strictly drop referrer information on all outbound requests.
+
+## 2025-02-21 - [Prevent swallowed exception tracebacks in Exception Handler]
+**Vulnerability:** The `unhandled_exception_handler` middleware caught all internal exceptions returning generic 'Internal Server Error' 500 response while ignoring explicitly logging the exceptions `log.error`, resulting in silently swallowed tracebacks server side.
+**Learning:** Returning a safe generic error response prevents internal application stack trace exposure, but it's important to make sure exceptions tracebacks are logged properly on the server side to detect attacks/bugs in the internal app code stack.
+**Prevention:** Ensured the custom unhandled exception handler properly logs the exception using `log.error("Unhandled exception", exc_info=_exc)` instead of ignoring it silently.
diff --git a/src/tacet/serve/server.py b/src/tacet/serve/server.py
index 2df2279..656faff 100644
--- a/src/tacet/serve/server.py
+++ b/src/tacet/serve/server.py
@@ -357,6 +357,7 @@ async def add_security_headers(request: Request, call_next):
 
     @app.exception_handler(Exception)
     async def unhandled_exception_handler(request: Request, _exc: Exception) -> Response:
+        log.error("Unhandled exception", exc_info=_exc)
         response = PlainTextResponse("Internal Server Error", status_code=500)
         return _apply_security_headers(response, request.url.path)