Fix Improper Error Handling in Sanic
Leaking stack traces is a primary vector for information disclosure. In Sanic, improper configuration or default error behavior can dump internal logic, environment variables, and library versions to an attacker. To harden a Sanic application, you must intercept the exception pipeline, suppress verbose debugging in production, and implement a centralized, sanitized response mechanism.
The Vulnerable Pattern
from sanic import Sanic, responseapp = Sanic(“InsecureApp”)
@app.get(“/debug-me”) async def trigger_error(request): # This will leak a full traceback to the client if debug=True # or if the default handler is not overridden. data = {} return response.json({“val”: data[‘missing_key’]})
if name == “main”: # CRITICAL: debug=True exposes the interactive debugger and tracebacks app.run(host=“0.0.0.0”, port=8000, debug=True)
The Secure Implementation
The secure implementation utilizes a custom `ErrorHandler` class to override Sanic's default exception behavior. By overriding the `default()` method, we ensure that every unhandled exception is caught, logged with full context to internal logs, and then mapped to a sanitized JSON response. This prevents the 'Sanic-Exception-Page' from rendering in the browser. Furthermore, setting `debug=False` is mandatory for production to disable the auto-reload and the built-in debugger, which are known entry points for RCE and info-leakage.
from sanic import Sanic, response from sanic.handlers import ErrorHandler import loggingclass UnifiedErrorHandler(ErrorHandler): def default(self, request, exception): # Log the actual traceback internally for the SOC/Dev team logging.error(f”Exception occurred: {exception}”, exc_info=True)
# Determine status code status_code = getattr(exception, "status_code", 500) # Return a generic, sanitized payload to the user return response.json( { "error": "Internal Server Error", "message": "An unexpected error occurred. Please contact support.", "trace_id": getattr(request, "id", "N/A") }, status=status_code )app = Sanic(“SecureApp”, error_handler=UnifiedErrorHandler())
@app.get(“/safe-route”) async def safe_handler(request): data = {} return response.json({“val”: data[‘missing_key’]})
if name == “main”: # Ensure debug is False and access_log is configured for production app.run(host=“0.0.0.0”, port=8000, debug=False, access_log=True)
Your Sanic API
might be exposed to Improper Error Handling
74% of Sanic apps fail this check. Hackers use automated scanners to find this specific flaw. Check your codebase before they do.
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