Open Redirect in Flask with Cockroachdb

An Open Redirect in a Flask application that uses Cockroachdb typically occurs when a route accepts a user-supplied URL or location parameter and performs an HTTP redirect without strict validation. If the application uses Cockroachdb as a backend data store, the redirect logic may read or construct redirection targets from database records or query parameters. Because Cockroachdb is a distributed SQL database, it does not introduce web framework behavior, but the way Flask interacts with Cockroachdb can inadvertently support an attacker-controlled redirect chain.

Consider a Flask route that retrieves a landing page configuration from Cockroachdb based on a tenant or campaign identifier, then redirects the user to a stored URL. If the stored URL is user-controlled or not validated against a whitelist, an attacker can craft a request such as /login?next=https://evil.example.com, and Flask can issue a 302 to that external domain. Even when using Cockroachdb to store legitimate redirect targets, if the application trusts database values without validating scheme and host, the redirect becomes unsafe. The presence of Cockroachdb does not cause the flaw; the risk arises from insecure handling of user input and unchecked redirect targets retrieved from any backend, including Cockroachdb.

In some cases, an API endpoint scanned by middleBrick might surface an Open Redirect finding when a Flask route uses query parameters or path variables to determine the redirect location, and the route does not enforce a strict allowlist of domains. MiddleBrick tests unauthenticated attack surfaces, so it can detect endpoints that redirect to external hosts based on unchecked inputs. Because Cockroachdb often serves as a backend for multi-tenant or high-availability apps, developers may assume database-driven configurations are safe, but validation must still occur in the application layer.

To remediate Open Redirect in Flask with Cockroachdb, validate and normalize any redirect target before using it in a response. Avoid using raw user input or unchecked database fields as the destination. Instead, use an allowlist of trusted domains or a mapping of safe keys to predefined URLs. Below are concrete code examples demonstrating secure patterns.

Safe redirect with an allowlist

Define a small set of allowed hosts and ensure the redirect target matches one of them. Use urllib.parse to parse and validate the URL before issuing a redirect.

from flask import Flask, request, redirect, abort
from urllib.parse import urlparse
import psycopg2

app = Flask(__name__)

ALLOWED_REDIRECT_HOSTS = {'app.example.com', 'static.example.com'}

def is_safe_url(url: str) -> bool:
    parsed = urlparse(url)
    return parsed.scheme in ('https', 'http') and parsed.netloc in ALLOWED_REDIRECT_HOSTS

@app.route('/login')
def login():
    next_param = request.args.get('next', '')
    if next_param and is_safe_url(next_param):
        return redirect(next_param)
    # Default safe location
    return redirect('/dashboard')

# Example Cockroachdb lookup for tenant configuration (safe when combined with validation)
def get_tenant_redirect_url(tenant_id: str) -> str | None:
    conn = psycopg2.connect(
        dbname=os.getenv('DB_NAME'),
        user=os.getenv('DB_USER'),
        password=os.getenv('DB_PASSWORD'),
        host=os.getenv('DB_HOST'),
        port=os.getenv('DB_PORT')
    )
    try:
        with conn.cursor() as cur:
            cur.execute(
                'SELECT redirect_url FROM tenant_config WHERE tenant_id = %s',
                (tenant_id,)
            )
            row = cur.fetchone()
            return row[0] if row else None
    finally:
        conn.close()

@app.route('/tenant-landing')
def tenant_landing():
    tid = request.args.get('tid', '')
    db_url = get_tenant_redirect_url(tid)
    if db_url and is_safe_url(db_url):
        return redirect(db_url)
    return redirect('/default')

Key remediation points

• Always parse URLs with urlparse and validate the scheme and netloc.
• Use an allowlist rather than a blocklist for hosts; avoid redirecting to IP addresses unless explicitly required and safe.
• Treat database values as untrusted input; validate them the same way you would validate query parameters.
• Provide a safe default redirect when input is missing or invalid, avoiding open redirects entirely.

By combining strict URL validation with Cockroachdb queries, Flask applications can safely use stored redirect targets without exposing users to open redirect abuse. MiddleBrick scans can verify that such validation is consistently applied across endpoints.