Fix Unrestricted Resource Consumption in Sanic
Sanic's high-performance nature makes it a prime target for resource exhaustion. Without explicit constraints, an attacker can trigger Out-of-Memory (OOM) kills or CPU starvation by flooding the event loop with massive payloads, slow-reading connections, or unbound concurrent requests. In the world of AppSec, if you don't limit it, they will abuse it.
The Vulnerable Pattern
from sanic import Sanic, responseapp = Sanic(“VulnerableApp”)
VULNERABILITY: No global limits on request size or timeouts.
An attacker can send a multi-gigabyte POST body to exhaust RAM.
@app.post(“/data”) async def ingest(request): return response.json({“received”: len(request.body)})
if name == “main”: app.run(host=“0.0.0.0”, port=8000)
The Secure Implementation
The secure implementation applies four critical layers of defense. First, 'REQUEST_MAX_SIZE' prevents memory exhaustion by dropping connections that exceed the defined byte limit before the body is fully buffered. Second, 'REQUEST_TIMEOUT' and its siblings prevent attackers from holding connections open indefinitely (Slowloris). Third, rate limiting via 'sanic-limiter' throttles abusive clients at the application layer. Finally, controlling the number of workers and disabling verbose access logging reduces CPU overhead and disk I/O during a flood.
from sanic import Sanic, response from sanic_limiter import Limiter, get_remote_addressapp = Sanic(“SecureApp”)
1. Enforce strict payload limits (e.g., 1MB)
app.config.REQUEST_MAX_SIZE = 1_000_000
2. Mitigate Slowloris by setting aggressive timeouts
app.config.REQUEST_TIMEOUT = 10 app.config.RESPONSE_TIMEOUT = 10 app.config.KEEP_ALIVE_TIMEOUT = 5
limiter = Limiter(app, key_func=get_remote_address)
@app.post(“/data”) @limiter.limit(“10 per minute”) # 3. Prevent API flooding async def ingest(request): return response.json({“status”: “safe”})
if name == “main”: # 4. Limit concurrency at the worker level app.run(host=“0.0.0.0”, port=8000, workers=4, access_log=False)
Your Sanic API
might be exposed to Unrestricted Resource Consumption
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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