A recent vulnerability discovered in an UK National Health Service HS API has once again highlighted the risks associated with insecure mobile application programming interfaces (APIs). The flaw reportedly allowed unauthorized access to sensitive patient data, raising serious concerns about the security of healthcare applications.

This incident underscores a broader issue in mobile security: APIs are the most vulnerable attack vector in modern applications. While organizations invest heavily in securing their back-end infrastructure, they often overlook the security of the APIs that bridge mobile apps and sensitive databases. APIs, when left unprotected, become open doors for attackers.

In this blog, we’ll examine why mobile APIs are often the weak link, how attackers exploit them, and how a zero-trust security approach—including mobile app attestation and runtime API security—can mitigate these risks. Drawing insights from Approov’s security solutions, we’ll highlight best practices that organizations should adopt to prevent similar incidents in the future.

Understanding the NHS API Flaw

The reported vulnerability in the NHS system exposed patient data through a poorly secured API. While exact details are still emerging, such flaws typically arise due to:

1. Lack of Proper Authentication – APIs that don’t strictly verify app requests allow attackers to access sensitive data.
2. Static API Keys Embedded in Apps – Many developers store API keys inside the mobile app itself, making it easy for attackers to extract them.
3. Insufficient Certificate Pinning – Without proper certificate validation, attackers can perform Man-in-the-Middle (MitM) attacks to intercept API traffic.
4. Absence of Runtime Protection – Attackers can easily reverse-engineer apps, modify API requests, and exploit backend vulnerabilities.

How do attackers exploit these weaknesses? They decompile the app, analyze API traffic, and use automated scripts to mimic legitimate requests. In the worst-case scenario, they gain access to large amounts of sensitive data, as was the case in the NHS breach.

A Zero-Trust Approach: Securing APIs with Mobile App Attestation

Traditional API security focuses on user authentication (e.g., passwords, multi-factor authentication), but this is not enough. Attackers don’t need user credentials if they can impersonate a legitimate app.

This is where mobile app attestation and runtime security come in.

1. Preventing Unauthorized API Access

One of the key takeaways from the NHS API flaw is that only genuine, untampered mobile apps should be allowed to communicate with backend services. Mobile app attestation solutions, such as Approov, ensure that:

• Only legitimate app instances running on uncompromised devices can access APIs.
• Cloned, repackaged, or manipulated apps are blocked from making API requests.
• Bots and scripts pretending to be real users are rejected at the API gateway.

Approov achieves this by verifying the mobile app at runtime before it is granted access to an API, ensuring attackers cannot use stolen API keys or manipulate requests.

2. Eliminating API Key Theft

One of the most common API security failures is hardcoding API keys inside mobile apps. Attackers can extract these keys from decompiled applications and use them to make unauthorized API requests.

Approov prevents this by enabling dynamic API key management, where API keys are:

• Never stored inside the app.
• Only delivered at runtime to attested, legitimate app instances.
• Revoked instantly if an app is detected to be running in a compromised environment.

This ensures that even if an attacker gains access to the mobile app’s code, they cannot extract usable API keys.

3. Defending Against Man-in-the-Middle (MitM) Attacks

TLS encryption is not enough. Attackers can install root certificates or use tools like Frida and mitmproxy to intercept API traffic.

Approov addresses this by implementing dynamic certificate pinning, ensuring that:

• The mobile app only communicates with trusted servers.
• Attackers cannot inject their own certificates to intercept data.
• Pinning updates happen dynamically, avoiding the common pitfall of certificate expiration breaking app functionality.

Moving Forward: Lessons for Organizations

The NHS API flaw is not an isolated case. Similar API vulnerabilities have been found in financial, healthcare, and government applications. To prevent these types of breaches, organizations must:

1. Implement Mobile App Attestation – Ensure that only verified apps can communicate with backend services.
2. Eliminate Static API Keys – Use dynamic secrets management to prevent key extraction.
3. Enforce Certificate Pinning – Prevent attackers from intercepting API traffic.
4. Monitor API Traffic for Anomalies – Use AI-driven security tools to detect abnormal API usage patterns.
5. Adopt a Zero-Trust Security Model – Never assume that an API request is legitimate unless it is verified.

Conclusion

The NHS API vulnerability highlights a widespread issue in mobile security: organizations focus on backend protection but neglect API security. The reality is that APIs are the new attack surface, and securing them requires a mobile-first security strategy.

By leveraging mobile app attestation, runtime API security, and dynamic key management, organizations can ensure that their APIs remain invisible and inaccessible to attackers.

Mobile security is not just about the device—it’s about ensuring trust across the entire digital ecosystem. As attackers evolve, security strategies must evolve too.

Has your organization assessed its mobile API security?

If you’re concerned about API vulnerabilities in your mobile apps, start by evaluating your API authentication, key management, and runtime security posture. It’s time to adopt a proactive approach to API security before the next breach happens.

Approov are experts on app and API security. We would be happy to set up a call to see if we can help you quickly and effectively improve your healthcare app security.