Hacking Mobile APIs: Real-World Exploits and How to Defend Against Them

Al-Amir Badmus

Introduction: Why Mobile API Security Matters Now More Than Ever

Mobile applications rely heavily on APIs—responsible for over 85% of their functionality. These APIs facilitate critical communication between mobile front-ends and back-end services. But with great power comes great risk. In a session packed with real-world demonstrations at APIsec|CON '25, Amir, a seasoned security engineer and APIsec University Ambassador, illustrated how easily attackers can exploit poorly secured mobile APIs—and why DevSecOps professionals need to take this threat seriously.

The Anatomy of Mobile API Vulnerabilities

Amir kicked off by explaining that what users see on their mobile screens is often a sanitized subset of the data returned by backend APIs. Attackers can exploit these APIs to retrieve and manipulate far more data than intended.

Here are the key vulnerabilities he addressed:

• Broken Authentication: Developers often hard-code sensitive information like usernames, passwords, API tokens, or JWTs into the mobile binary. This is low-hanging fruit for attackers who reverse-engineer the app.
• Insufficient Encryption: Many developers skip proper encryption for data in transit. Tools like Burp Suite can intercept unencrypted traffic, especially when SSL pinning is misconfigured or bypassed.
• Excessive Data Exposure: APIs may return more data than needed—such as account balances or admin flags—which can be harvested for further exploitation.
• Mass Assignment: Attackers can manipulate hidden fields like isAdmin: false in API responses. By changing these values and resubmitting them, they can escalate privileges or inflate account balances.
• Lack of Rate Limiting: Without proper throttling, attackers can brute-force credentials, enumerate accounts, or exploit IDOR (Insecure Direct Object Reference) vulnerabilities at scale.

Live Demo: Hacking a Mobile Banking App

To drive his points home, Amir used a vulnerable mobile banking app called Vuln Bank Mobile, which he built specifically for training purposes. Key steps in the demo included:

1. Installing the APK on an emulator.
2. Proxying Traffic via Burp Suite, with certificates automated using custom scripts.
3. Intercepting API Calls and viewing sensitive data like account balances and admin flags.
4. Privilege Escalation by manipulating JSON payloads to set isAdmin: true.
5. Balance Inflation through tampering with transfer endpoints using negative values or large integers.
6. Accessing Web Admin Panels using elevated privileges originally obtained through the mobile app.

This powerful walkthrough illustrated how even seemingly secure apps can leak sensitive information and expose dangerous functionality through unsecured APIs.

Mitigation Strategies for DevSecOps Teams

To counter these attacks, Amir emphasized a defense-in-depth approach:

1. Strong Authentication & Authorization: Implement robust password policies and access controls. Never hard-code credentials into the app binary.
2. Data Minimization & Encryption: Only expose necessary data. Use TLS with SSL pinning and encrypt sensitive data at rest and in transit.
3. Proper Rate Limiting & Input Validation: Prevent brute-force attacks and mass enumeration. Always validate inputs on the server side.
4. Implement Security Testing Pipelines:
   • Manual Testing: Using tools like Burp Suite for hands-on testing.
   • Automated Testing: Leverage solutions like APIsec's scanner to achieve broad coverage across hundreds of endpoints.
5. Regular Pentesting and Threat Modeling: Integrate security reviews early in the development lifecycle. Keep security an ongoing process, not a final checkbox.

Final Thoughts: Secure Your APIs, Secure Your Business

APIs are the connective tissue of mobile applications—but they’re also prime targets for attackers. Amir’s presentation underscores the importance of proactive security practices. By implementing secure design principles, rate-limiting, encryption, and continuous testing, AppSec and DevSecOps professionals can greatly reduce their attack surface and defend against even the most sophisticated API exploits.

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