🛡️ Sentinel: [HIGH] Fix timing attack and information disclosure vulnerabilities

[ivanleekk]

🚨 Severity: HIGH
💡 Vulnerability:

1. Timing attack vulnerability in /internal/tasks/daily-snapshot endpoint when comparing x_scheduler_secret to the expected secret using the != operator.
2. Information disclosure vulnerability where raw exception details (str(e)) were leaked to the client in HTTP 500 error responses on the same endpoint.
   🎯 Impact:
3. An attacker could potentially guess the SCHEDULER_SECRET character-by-character by measuring the time taken to process the request, leading to unauthorized access to the daily snapshot scheduled job.
4. An attacker could intentionally trigger an exception to gain insights into the application's internal workings, database errors, or stack traces, facilitating further attacks.
   🔧 Fix:
5. Replaced the standard inequality check with secrets.compare_digest to perform constant-time comparison, effectively mitigating the timing attack.
6. Replaced the generic except Exception as e: catch block with an explicit logging.error(..., exc_info=True) for server-side observability, and masked the client-facing HTTP response with a generic "Internal server error" message to prevent information leakage.
   ✅ Verification:
   Verified code changes by manually inspecting the modified file. Ran uv run ruff check and the backend pytest suite locally to ensure no regressions were introduced. Evaluated security impacts via code review.

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PR created automatically by Jules for task 1094861012358567233 started by @ivanleekk

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