**Vulnerability:** The Telegram Deployment Bot (`scripts/telegram_deploy_bot.py`) contained a "Fail Open" vulnerability where omitting the `TELEGRAM_ALLOWED_USER_IDS` environment variable resulted in granting access to *all* Telegram users instead of *none*.
**Learning:** Security controls must default to deny (Fail Closed). Implicitly allowing access when configuration is missing creates silent vulnerabilities that are hard to detect until exploited.
**Prevention:** Ensure all authorization checks explicitly return `False` or throw an exception if the access control list is empty or undefined. Never default to `True` in security-critical paths.
## 2026-02-27 - [Code Quality] Secure Error Logging vs Printing
**Vulnerability:** The Web Dashboard (`scripts/web_dashboard.py`) was leaking raw exception strings to users (`return f"Error: {e}", 500`). While fixing this to return a generic error, the initial fix used `print(e, file=sys.stderr)`.
**Learning:** Using `print` to stderr for exceptions is insufficient for production debugging as it loses the stack trace, making root cause analysis difficult while still hiding details from users.
**Prevention:** Always use `logging.exception("Message")` in `except` blocks. This automatically captures and logs the full stack trace securely to the server logs while allowing the application to return a sanitized, generic error message to the user.
