Fix SQL Injection (Legacy & Modern) in Sanic
SQL Injection in Sanic occurs when untrusted user input is concatenated directly into SQL queries, bypassing the database driver's safety mechanisms. In an asynchronous environment like Sanic, this can lead to full database compromise, data exfiltration, or authentication bypass. As a Senior AppSec Researcher, I see this most often when developers try to 'speed up' development by using f-strings or format() instead of proper parameterization or ORM abstractions.
The Vulnerable Pattern
from sanic import Sanic, response import aiopgapp = Sanic(“VulnerableApp”)
@app.get(“/user/<user_id>”) async def get_user(request, user_id): async with aiopg.connect(dsn=“dbname=test user=postgres”) as conn: async with conn.cursor() as cur: # DANGER: Direct string interpolation allows attackers to escape the query # Payload example: /user/1’ OR ‘1’=‘1 query = f”SELECT * FROM users WHERE id = ‘{user_id}’” await cur.execute(query) result = await cur.fetchall() return response.json(result)
The Secure Implementation
The vulnerability exists because the DB engine cannot distinguish between command logic and user data when they are merged into a single string. The 'Legacy' fix utilizes DB-API 2.0 parameterization, where the driver sends the query template and the data separately to the server, ensuring the input is treated strictly as a literal value. The 'Modern' fix employs an ORM (Tortoise-ORM) and Sanic's built-in path parameter validation (
from sanic import Sanic, response from tortoise.models import Model from tortoise import fieldsModern Approach: Tortoise-ORM with Type Hinting
class Users(Model): id = fields.IntField(pk=True) username = fields.CharField(max_length=50)
app = Sanic(“SecureApp”)
@app.get(“/user/<user_id:int>”) async def get_user_modern(request, user_id: int): # ORM automatically uses prepared statements user = await Users.filter(id=user_id).first() return response.json({“user”: user.username} if user else {})
Legacy Approach: Driver-Level Parameterization
@app.get(“/legacy/user/<user_id:int>”) async def get_user_legacy(request, user_id: int): async with aiopg.connect(dsn=”…”) as conn: async with conn.cursor() as cur: # Secure: Use placeholders (%s) and pass data as a separate tuple await cur.execute(“SELECT * FROM users WHERE id = %s”, (user_id,)) return response.json(await cur.fetchall())
Your Sanic API
might be exposed to SQL Injection (Legacy & Modern)
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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