🛡️ Sentinel: [CRITICAL] Fix info disclosure and timing attack vulnerabilities in internal router

[ivanleekk]

🚨 Severity: CRITICAL
💡 Vulnerability: The internal daily-snapshot cronjob endpoint (/internal/tasks/daily-snapshot) had two critical vulnerabilities:

1. Timing Attack: The verify_scheduler_secret dependency used standard string comparison (!=) for validating the scheduler secret, allowing an attacker to theoretically guess the token character by character based on response times.
2. Information Disclosure: The scheduled_snapshot_job leaked raw Python exception stack traces and strings (str(e)) directly to the client in HTTP 500 error responses, potentially exposing database states, column names, or other internal application context.

🎯 Impact: Attackers could bypass authentication by guessing the scheduler secret, allowing them to repeatedly trigger massive database snapshot runs (DoS attack vector), and could mine the server for internal schema or backend state context via forced generic 500 exceptions.

🔧 Fix:

1. Replaced x_scheduler_secret != expected_secret with Python's secure secrets.compare_digest function. Added a check for None to prevent TypeError.
2. Modified the catch block from except Exception as e: to except Exception:, catching the error to log internally using Python's standard logging library with exc_info=True for debugging, while serving a sanitized, generic 500 error response to the client.

✅ Verification:

• Reviewed the modifications using manual verification (cat, diff).
• Ran Python linters (uv run ruff check) to ensure valid formatting and module-level import locations.
• Ran backend pytest suite, observing the same passing/failing state as pre-patch tests, ensuring no logic regressions were introduced.

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PR created automatically by Jules for task 13062859209899411874 started by @ivanleekk

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