Fix Broken User Authentication in Sanic
Broken Authentication in Sanic apps usually stems from weak hashing algorithms, predictable session identifiers, or lack of secure cookie attributes. In a high-performance async environment, developers often sacrifice security for speed. We're going to kill that habit by implementing Argon2id hashing and cryptographically secure session management.
The Vulnerable Pattern
from sanic import Sanic, response
import hashlib
app = Sanic(“VulnApp”)
VULNERABILITY: Using MD5 (fast, collision-prone) and predictable cookies
users = {“admin”: hashlib.md5(“password123”.encode()).hexdigest()}
@app.post(“/login”)
async def login(request):
user = request.json.get(“username”)
pwd = request.json.get(“password”)
hashed_pwd = hashlib.md5(pwd.encode()).hexdigest()
if users.get(user) == hashed_pwd:
res = response.json({"status": "success"})
# VULNERABILITY: Session ID is just the username (predictable)
res.cookies["session"] = user
return res
return response.json({"status": "fail"}, status=401)</code></pre>
The Secure Implementation
The fix addresses three critical failures: 1. Password Hashing: Swapped MD5 for Argon2id, which is computationally expensive and memory-hard, making brute-force attacks unfeasible. 2. Session Entropy: Replaced predictable usernames with 256-bit entropy strings using 'secrets', preventing session hijacking via guessing. 3. Transport Security: Applied 'HttpOnly' to prevent XSS from stealing cookies, 'Secure' to enforce HTTPS-only transmission, and 'SameSite=Strict' to neutralize CSRF vectors.
from sanic import Sanic, response
from passlib.hash import argon2
import secrets
app = Sanic(“SecureApp”)
FIX: Use Argon2id (memory-hard, resistant to GPU cracking)
users = {“admin”: argon2.hash(“complex_password_99”)}
@app.post(“/login”)
async def login(request):
data = request.json
username, password = data.get(“username”), data.get(“password”)
stored_hash = users.get(username)
if stored_hash and argon2.verify(password, stored_hash):
res = response.json({"message": "authenticated"})
# FIX: Generate high-entropy session tokens
session_id = secrets.token_urlsafe(32)
res.cookies["session_id"] = session_id
# FIX: Hardened cookie flags
res.cookies["session_id"]["httponly"] = True
res.cookies["session_id"]["secure"] = True
res.cookies["session_id"]["samesite"] = "Strict"
return res
return response.json({"error": "Unauthorized"}, status=401)</code></pre>
Your Sanic API
might be exposed to Broken User Authentication
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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