Token Leakage in Flask with Cockroachdb

Token leakage occurs when authentication tokens, session identifiers, or API keys are exposed in logs, error messages, HTTP headers, or responses. In a Flask application using CockroachDB, the combination of a Python web framework with a distributed SQL database can inadvertently expose tokens through misconfigured error handling, insecure logging, or improper use of database drivers.

Flask’s default development server is not designed for production and can expose detailed tracebacks that include variables, configuration values, or request context. When a CockroachDB connection fails or a query is malformed, Flask may surface database-specific error messages that contain token values if they are embedded in query strings or passed through exception objects. For example, if a token is included as a parameter in a raw SQL string and an error occurs, the stack trace may reveal the token to an attacker who sees the error page or log entry.

CockroachDB’s wire protocol and driver behavior can also contribute to leakage. The psycopg2 or cockroachdb Python driver may include query parameters in debug output or logs when exceptions are raised. If Flask logs full request bodies or query parameters at DEBUG level, and those logs contain authentication tokens (e.g., in headers or URL query strings), the tokens become persistent artifacts accessible to anyone with log access.

Another vector is improper handling of redirect URLs or callback endpoints. Flask routes that accept a redirect_uri parameter and pass it to CockroachDB for storage or logging can expose tokens if the redirect includes sensitive query parameters. An attacker could craft a malicious link that triggers a request with a token, and if Flask logs the full URL to CockroachDB-related operations, the token is stored in plaintext or weakly hashed logs.

Additionally, if the application uses CockroachDB’s changefeeds or export features to stream data for debugging or monitoring, tokens present in application data may be inadvertently included in those streams. Without strict schema design and token masking at the application layer, sensitive authentication material can appear in unintended database-side outputs.

These risks are detectable by middleBrick’s LLM/AI Security checks and Data Exposure scans, which flag endpoints that handle tokens without proper isolation or encryption. The scanner identifies places where tokens may appear in logs, error responses, or database interactions, providing prioritized findings with remediation guidance to reduce the attack surface.

To prevent token leakage in Flask applications using CockroachDB, follow these concrete coding practices that isolate tokens from database operations and logging.

1. Use environment variables and configuration abstraction to keep tokens out of code and logs:

import os
from flask import Flask

app = Flask(__name__)
app.config['SECRET_KEY'] = os.environ.get('SECRET_KEY')
app.config['COCKROACHDB_URI'] = os.environ.get('COCKROACHDB_URI')

if not app.config['SECRET_KEY'] or not app.config['COCKROACHDB_URI']:
    raise RuntimeError('Missing required environment variables')

This ensures tokens are never hardcoded or logged as part of application source code.

2. Parameterize all database queries to avoid token inclusion in error messages:

import psycopg2
from flask import g

def get_db():
    if 'db' not in g:
        g.db = psycopg2.connect(app.config['COCKROACHDB_URI'])
    return g.db

@app.route('/user/')
def get_user(user_id):
    db = get_db()
    try:
        with db.cursor() as cur:
            # Use parameterized queries to prevent token leakage in errors
            cur.execute('SELECT id, email FROM users WHERE id = %s', (user_id,))
            return cur.fetchone()
    except Exception as e:
        # Log generic errors without query details
        app.logger.error('Database query failed')
        return {'error': 'Internal server error'}, 500

Parameterized queries ensure that user input and tokens are never interpolated into SQL strings, reducing the chance that they appear in exception details.

3. Disable detailed error messages and debug logging in production:

if __name__ == '__main__':
    # Never run with debug=True in production
    app.run(debug=False, host='0.0.0.0', port=5000)

Setting debug=False prevents Flask from rendering tracebacks that may include token values. Combine this with structured logging that redacts sensitive fields before writing to CockroachDB-backed log stores.

4. Validate and sanitize all inputs that interact with authentication flows:

from flask import request, jsonify
import re

def validate_token_format(token):
    # Example: Bearer token pattern
    pattern = r'^Bearer [a-zA-Z0-9\-_=]+\.[a-zA-Z0-9\-_=]+\.?[a-zA-Z0-9\-_.+/=]*$'
    return re.match(pattern, token) is not None

@app.before_request
def protect_token_endpoints():
    if request.path.startswith('/api/'):
        auth = request.headers.get('Authorization', '')
        if not validate_token_format(auth):
            return jsonify({'error': 'Unauthorized'}), 401

Validating token format before using it in CockroachDB operations prevents malformed tokens from triggering verbose errors that expose internal state.

5. Avoid storing raw tokens in database tables; store references or hashes instead:

# Store only token metadata, never the raw token
cur.execute('''
    INSERT INTO api_tokens (user_id, fingerprint, expires_at)
    VALUES (%s, %s, %s)
''', (user_id, token_fingerprint, expires_at))

This approach ensures that even if logs or backups are compromised, raw tokens are not recoverable from CockroachDB.