Overcoming Geo-Restrictions in Legacy TypeScript Codebases for Security Testing

#security #typescript #legacy

Implementing geo-restrictions is a common practice for content providers and service platforms. However, security researchers often need to test and verify these geo-blocked features during development or penetration testing phases. In legacy TypeScript codebases, this task can be challenging due to tightly coupled configuration logic, lack of modularity, and limited support for dynamic environment simulation. This article explores practical techniques for simulating geographic locations within existing code to evaluate geo-blocking mechanisms effectively.

Understanding the Challenge

Legacy TypeScript applications frequently embed geo-specific logic directly within client or server code, often relying on IP-based detection, request headers, or hardcoded configuration values. This coupling complicates the process of testing different geographic scenarios without deploying multiple environment configurations or modifying source code. Security researchers need a robust, non-intrusive method to simulate different locations during testing.

Interception and Modification of Request Headers

A straightforward approach involves intercepting HTTP requests and manipulating geolocation indicators such as headers or cookies. Many geo-restriction systems leverage headers like X-Forwarded-For, Accept-Language, or custom headers to determine user location.

// Middleware to override IP address for testing
app.use((req, res, next) => {
  // Simulate a US IP
  req.headers['X-Forwarded-For'] = '203.0.113.195';
  // Alternatively, override locale
  req.headers['Accept-Language'] = 'en-US';
  next();
});

Using this middleware, a researcher can rotate IP addresses or language headers to trigger various geo-restriction responses without altering production code.

Mocking External Geolocation Services

Many applications use external geolocation APIs or databases, which pose a challenge for local testing. To emulate different geographies, you can mock these external calls in the runtime environment.

// Mock geolocation service
const geoService = {
  getLocation: (ip: string) => {
    // Return research-driven location based on IP
    if (ip === '203.0.113.195') {
      return { country: 'US', city: 'New York' };
    }
    // Default
    return { country: 'Unknown', city: 'Unknown' };
  }
};

// Usage in code
const userIP = req.headers['X-Forwarded-For'] || req.connection.remoteAddress;
const location = geoService.getLocation(userIP);
// Trigger geo-restriction based on 'location'

By replacing actual API calls with mocks, security testers can simulate all geographic regions without expensive infrastructure changes.

Configuring Environment Variables and Feature Flags

In more advanced scenarios, legacy systems may read geographic restrictions from environment variables or feature flags. Temporarily adjusting these during testing can reveal how the system behaves under different geo-restriction policies.

// Example feature flag setup
const geoBlockingEnabled = process.env.GEO_BLOCK_ENABLED === 'true';
const testRegion = process.env.TEST_REGION || 'US';

if (geoBlockingEnabled) {
  // Logic to block or allow based on 'testRegion'
  if (userLocation.country !== testRegion) {
    res.status(403).send('Content Unavailable in Your Location');
  }
}

Testers can modify environment variables at runtime or integrate with container orchestration tools for dynamic testing.

Practical Recommendations

Maintain a separate testing environment with configurable headers or environment variables.
Implement request interception to manipulate geolocation headers.
Mock external geo-services to simulate different regions.
Use feature flags to toggle geo-restrictions dynamically.
Document assumptions about how geolocation is determined to streamline testing efforts.

By systematically intercepting, mocking, and configuring geo-location inputs, security researchers can bypass the limitations of legacy codebases and conduct comprehensive geo-restriction testing effectively. This approach ensures robust evaluation of security controls and compliance without the need for intrusive code modifications or duplicative infrastructure.