Performing Dynamic Analysis of Android App

When to Use

Use this skill when:

• Static analysis results need runtime validation on an actual Android device
• The target app uses obfuscation (DexGuard, custom packers) that prevents effective static analysis
• Testing requires observing actual API calls, decrypted data, or runtime-generated values
• Assessing root detection, tamper detection, or anti-debugging implementations

Do not use this skill on production environments without authorization -- dynamic instrumentation can alter app behavior and trigger security alerts.

Prerequisites

• Rooted Android device or emulator (Genymotion, Android Studio AVD with writable system)
• Frida server installed on device matching the architecture (arm64, x86_64)
• Python 3.10+ with frida-tools and objection packages
• ADB configured and device connected
• Target APK installed on device

Workflow

Step 1: Setup Frida Server on Android Device

# Check device architecture
adb shell getprop ro.product.cpu.abi
# Output: arm64-v8a

# Download matching Frida server from GitHub releases
# https://github.com/frida/frida/releases
# Push to device
adb push frida-server-16.x.x-android-arm64 /data/local/tmp/frida-server
adb shell chmod 755 /data/local/tmp/frida-server
adb shell /data/local/tmp/frida-server &

# Verify Frida connection
frida-ps -U

Step 2: Enumerate Application Attack Surface

# List all packages
frida-ps -U -a

# Attach Objection for high-level exploration
objection --gadget com.target.app explore

# List activities, services, receivers
android hooking list activities
android hooking list services
android hooking list receivers

# List loaded classes
android hooking list classes
android hooking search classes com.target.app

Step 3: Hook Sensitive Methods

# Hook all methods of a class
android hooking watch class com.target.app.auth.LoginManager

# Hook specific method with argument dumping
android hooking watch class_method com.target.app.auth.LoginManager.authenticate --dump-args --dump-return

# Hook crypto operations
android hooking watch class javax.crypto.Cipher --dump-args
android hooking watch class java.security.MessageDigest --dump-args

# Hook network calls
android hooking watch class okhttp3.OkHttpClient --dump-args
android hooking watch class java.net.URL --dump-args

Step 4: Write Custom Frida Scripts for Deep Analysis

// hook_crypto.js - Intercept encryption/decryption operations
Java.perform(function() {
    var Cipher = Java.use("javax.crypto.Cipher");

    Cipher.doFinal.overload("[B").implementation = function(input) {
        var mode = this.getAlgorithm();
        console.log("[Cipher] Algorithm: " + mode);
        console.log("[Cipher] Input: " + bytesToHex(input));

        var result = this.doFinal(input);
        console.log("[Cipher] Output: " + bytesToHex(result));
        return result;
    };

    function bytesToHex(bytes) {
        var hex = [];
        for (var i = 0; i < bytes.length; i++) {
            hex.push(("0" + (bytes[i] & 0xFF).toString(16)).slice(-2));
        }
        return hex.join("");
    }
});

# Execute custom Frida script
frida -U -f com.target.app -l hook_crypto.js --no-pause

Step 5: Bypass Root Detection

// root_bypass.js - Common root detection bypass
Java.perform(function() {
    // Bypass RootBeer library
    var RootBeer = Java.use("com.scottyab.rootbeer.RootBeer");
    RootBeer.isRooted.implementation = function() {
        console.log("[RootBeer] isRooted() bypassed");
        return false;
    };

    // Bypass generic file-based root checks
    var File = Java.use("java.io.File");
    var originalExists = File.exists;
    File.exists.implementation = function() {
        var path = this.getAbsolutePath();
        var rootPaths = ["/system/app/Superuser.apk", "/system/xbin/su",
                         "/sbin/su", "/system/bin/su", "/data/local/bin/su"];
        if (rootPaths.indexOf(path) >= 0) {
            console.log("[Root] Blocked check for: " + path);
            return false;
        }
        return originalExists.call(this);
    };

    // Bypass SafetyNet/Play Integrity
    try {
        var SafetyNet = Java.use("com.google.android.gms.safetynet.SafetyNetApi");
        console.log("[SafetyNet] Class found - may need additional bypass");
    } catch(e) {}
});

Step 6: Analyze Network Communication at Runtime

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