flask-security-headers 1.0.2

Essential security utilities for Flask applications

Flask-Security-Headers

Essential security utilities for Flask applications - Prevent common vulnerabilities like open redirects, XSS attacks, and weak passwords with battle-tested helper functions.

Why Flask-Security-Headers?

Security shouldn't be an afterthought. This package provides production-ready security utilities that are:

• ✅ Battle-tested in production at WallMarkets
• ✅ Zero dependencies beyond Flask
• ✅ Easy to integrate - just import and use
• ✅ Well-documented with real-world examples

Features

🛡️ Open Redirect Prevention

Validate URLs before redirecting to prevent phishing attacks. Ensures redirects only go to your domain.

🔐 Password Strength Validation

Enforce strong passwords with customizable requirements:

• Minimum 8 characters
• Uppercase and lowercase letters
• Numbers and special characters
• Clear error messages for users

⏰ Fresh Login Requirement

Require recent authentication for sensitive operations (password changes, payment methods, etc.)

📁 Filename Sanitization

Prevent path traversal attacks by sanitizing uploaded filenames

🌐 Proxy-Aware IP Detection

Get the real client IP address, even behind proxies and load balancers

🔍 XSS Content Detection

Check user-submitted content for suspicious patterns before storing

Installation

pip install flask-security-headers

Quick Start

pip install flask-security-headers

Usage Examples

1. Safe URL Validation (Prevent Open Redirects)

from flask import redirect, request
from flask_security_headers import is_safe_url

@app.route('/redirect')
def safe_redirect():
    target = request.args.get('next', '/')
    if is_safe_url(target):
        return redirect(target)
    return redirect('/')

2. Require Fresh Login for Sensitive Operations

from flask_security_headers import require_fresh_login

@app.route('/settings/password', methods=['POST'])
@require_fresh_login(timeout_minutes=30)
def change_password():
    # User must have logged in within last 30 minutes
    pass

3. Password Strength Validation

from flask_security_headers import validate_password_strength

valid, msg = validate_password_strength(password)
if not valid:
    return {'error': msg}, 400

4. Filename Sanitization (Prevent Path Traversal)

from flask_security_headers import sanitize_filename

filename = sanitize_filename(request.files['file'].filename)
# Safe to use in file paths

5. Get Client IP (Proxy-Aware)

from flask_security_headers import get_client_ip

@app.route('/api/endpoint')
def endpoint():
    client_ip = get_client_ip()
    # Works correctly behind proxies, load balancers, CDNs
    app.logger.info(f"Request from {client_ip}")

6. Content Security Check

from flask_security_headers import check_content_security

@app.route('/comment', methods=['POST'])
def post_comment():
    content = request.form['comment']
    is_safe, message = check_content_security(content)
    
    if not is_safe:
        return {'error': f'Suspicious content detected: {message}'}, 400
    
    # Safe to store

Real-World Use Cases

E-commerce Platform

# Secure password reset flow
@app.route('/reset-password/<token>', methods=['POST'])
def reset_password(token):
    new_password = request.form['password']
    
    # Validate password strength
    valid, msg = validate_password_strength(new_password)
    if not valid:
        flash(msg, 'error')
        return redirect(url_for('reset_password', token=token))
    
    # Update password...
    
    # Safe redirect
    next_url = request.args.get('next', '/')
    if is_safe_url(next_url):
        return redirect(next_url)
    return redirect('/')

Admin Panel

# Require fresh login for critical operations
@app.route('/admin/delete-user/<int:user_id>', methods=['POST'])
@login_required
@require_fresh_login(timeout_minutes=15)
def delete_user(user_id):
    # User must have logged in within last 15 minutes
    # Prevents session hijacking from causing damage
    user = User.query.get_or_404(user_id)
    db.session.delete(user)
    db.session.commit()
    return redirect(url_for('admin.users'))

File Upload Service

@app.route('/upload', methods=['POST'])
def upload_file():
    file = request.files['document']
    
    # Sanitize filename to prevent path traversal
    safe_filename = sanitize_filename(file.filename)
    # "../../../etc/passwd" becomes "etc_passwd"
    
    file.save(os.path.join(app.config['UPLOAD_FOLDER'], safe_filename))

API Reference

is_safe_url(target: str) -> bool

Validates if a URL is safe for redirect (same domain).

validate_password_strength(password: str) -> Tuple[bool, Optional[str]]

Returns (True, None) if valid, or (False, error_message) if invalid.

require_fresh_login(timeout_minutes: int = 30)

Decorator that requires recent authentication.

sanitize_filename(filename: str) -> str

Removes dangerous characters and path components from filenames.

get_client_ip() -> str

Returns the real client IP, respecting proxy headers if configured.

check_content_security(content: str) -> Tuple[bool, str]

Checks content for suspicious patterns like script tags.

Configuration

# Enable proxy header trust (only if behind a trusted proxy!)
app.config['BEHIND_PROXY'] = True

# Customize password requirements (optional)
app.config['MIN_PASSWORD_LENGTH'] = 10
app.config['REQUIRE_SPECIAL_CHARS'] = True

Security Best Practices

1. Always validate redirects - Use is_safe_url() before any redirect()
2. Enforce strong passwords - Use validate_password_strength() on registration/password change
3. Require fresh login - Use @require_fresh_login() for sensitive operations
4. Sanitize filenames - Always use sanitize_filename() for user uploads
5. Log security events - Track failed validation attempts

Testing

pytest tests/

Production Usage

This package is used in production at:

• WallMarkets - Multi-vendor marketplace platform
• Handling thousands of daily requests
• Protecting sensitive user operations

Contributing

Contributions welcome! Please:

1. Fork the repository
2. Create a feature branch
3. Add tests for new functionality
4. Submit a pull request

License

MIT License - see LICENSE file for details

Support

• 📚 Documentation
• 🐛 Issue Tracker
• 💬 Discussions

Related Packages

• flask-ratelimit-simple - Rate limiting
• flask-supercache - Caching
• flask-querymonitor - Query optimization

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Made with ❤️ by the WallMarkets team