Fix Shadow API Exposure in Sanic
Shadow APIs in Sanic are undocumented, unmonitored endpoints that exist outside the security perimeter. These usually manifest as legacy Blueprints, forgotten debug routes, or overly permissive catch-all handlers. In Sanic's high-concurrency environment, these 'dark' routes are prime targets for unauthorized data exfiltration and parameter pollution.
The Vulnerable Pattern
from sanic import Sanic, responseapp = Sanic(“ShadowAPI_Demo”)
VULNERABILITY: Permissive catch-all route can expose internal logic
@app.route(“/path:path”) async def catch_all(request, path): return response.json({“debug_info”: f”Path {path} accessed”})
VULNERABILITY: Undocumented legacy endpoint left in code
@app.route(“/old_api/v1/debug_dump”) async def legacy_endpoint(request): return response.json({“env”: “prod”, “db”: “10.0.0.5”})
if name == “main”: # VULNERABILITY: Debug mode enabled in production app.run(host=“0.0.0.0”, port=8000, debug=True)
The Secure Implementation
To eliminate Shadow APIs, first disable Sanic's 'debug' mode in production to prevent the auto-generation of error pages and inspector routes. Second, move away from dynamic catch-all routing ('
from sanic import Sanic, response, Blueprint from sanic.config import Configclass ProductionConfig(Config): DEBUG = False STRICT_SLASHES = True
app = Sanic(“HardenedAPI”, config=ProductionConfig()) api_v2 = Blueprint(“v2”, url_prefix=“/api/v2”)
@api_v2.get(“/data”) async def get_data(request): return response.json({“status”: “authorized”})
SECURE: Explicit Blueprint registration
app.blueprint(api_v2)
SECURE: Explicit 404 handler to prevent path probing
@app.exception(Exception) async def handle_404(request, exception): return response.json({“error”: “Resource not found”}, status=404)
if name == “main”: # SECURE: Debug disabled, workers defined for production app.run(host=“0.0.0.0”, port=8000, debug=False, access_log=True)
Your Sanic API
might be exposed to Shadow API Exposure
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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