Frida Android Hooks

Use this skill when instrumenting Android Java/Kotlin/JNI behavior.

Setup Checks

1. Verify host and device versions match:

   frida --version
   adb shell /data/local/tmp/frida-server --version
   frida-ps -Uai

2. Use spawn for early initialization:

   frida -U -f com.example.app -l agent.js --no-pause

3. Use attach for behavior reachable after app startup:

   frida -U -n com.example.app -l agent.js

Java Hook Pattern

Java.perform(() => {
  const Target = Java.use("com.example.Target");
  Target.method.overload("java.lang.String").implementation = function (value) {
    console.log("[Target.method]", value);
    const result = this.method(value);
    console.log("[Target.method] ->", result);
    return result;
  };
});

Android Rules

• Always hook inside Java.perform() unless only native APIs are used.
• Resolve overloads explicitly. Do not rely on ambiguous method names.
• Hook constructors through $init.
• For Kotlin, expect companion classes, synthetic methods, default-argument helpers, and obfuscated names.
• If a class is not found, inspect class loaders and set Java.classFactory.loader to the app loader that can see it.
• For native methods, bridge to frida-native-hooks after identifying the loaded .so and JNI symbol.

Practitioner Patterns

• For obfuscated code, hook meaningful platform boundaries first: URL/request builders, JSON parsers, Base64, crypto, SharedPreferences, keystore, file I/O, WebView, class loading, and native library loading.
• Log Java stack traces on high-signal hooks to find the app-owned caller before writing app-specific hooks.
• Convert byte arrays deliberately. Print both hex and UTF-8/ASCII only when valid; binary crypto material is often not text.
• Hook reflection and dynamic loading when classes appear late: Class.forName, ClassLoader.loadClass, DexClassLoader, PathClassLoader, and Runtime.loadLibrary*.
• For TLS/pinning, identify the actual stack before bypassing: OkHttp/CertificatePinner, TrustManager, Conscrypt, WebView, Flutter/BoringSSL, or native custom validation.
• For root/emulator/integrity bypasses, avoid blind mega-scripts as the final answer. Use them to reveal checks, then keep the smallest hooks that change the target behavior.

Discovery Snippets

Java.perform(() => {
  const groups = Java.enumerateMethods("*crypto*!*/isu");
  console.log(JSON.stringify(groups, null, 2));
});

Java.perform(() => {
  Java.enumerateClassLoaders({
    onMatch(loader) {
      try {
        Java.classFactory.loader = loader;
        Java.use("com.example.Target");
        console.log("loader:", loader);
      } catch (_) {}
    },
    onComplete() {}
  });
});

Pinning and Auth Work

• Treat public bypass snippets as reconnaissance, not final proof.
• Identify the actual trust path: platform trust manager, OkHttp, Conscrypt, WebView, native TLS, custom signature, or backend challenge.
• Log inputs/outputs before replacing trust decisions.
• Preserve evidence: hooked class, stack trace, endpoint, certificate or hash material observed, and app version.

References

Read references/android-patterns.md for overload, constructor, class-loader, JNI, OkHttp, WebView, and spawn timing patterns.