Reverse Engineering Android Malware with JADX

When to Use

• A suspicious Android APK has been reported as malicious or flagged by mobile threat detection
• Analyzing Android banking trojans, spyware, SMS stealers, or adware samples
• Determining what data an app collects, where it sends it, and what permissions it abuses
• Extracting C2 server addresses, encryption keys, and configuration data from Android malware
• Understanding overlay attack mechanisms used by banking trojans

Do not use for analyzing obfuscated native (.so) libraries within APKs; use Ghidra or IDA for native ARM binary analysis.

Prerequisites

• JADX 1.5+ installed (download from https://github.com/skylot/jadx/releases)
• Android SDK with aapt2 and adb tools for APK inspection
• apktool for full APK disassembly including smali code and resources
• Python 3.8+ with androguard library for automated APK analysis
• Frida for dynamic instrumentation (optional, for runtime analysis)
• Isolated Android emulator (Genymotion or Android Studio AVD) without Google services

Workflow

Step 1: Extract APK Metadata and Permissions

Examine the APK structure and AndroidManifest.xml:

# Get APK basic info
aapt2 dump badging malware.apk

# Extract AndroidManifest.xml
apktool d malware.apk -o apk_extracted/ -f

# Analyze permissions with androguard
python3 << 'PYEOF'
from androguard.core.apk import APK

apk = APK("malware.apk")

print(f"Package:    {apk.get_package()}")
print(f"App Name:   {apk.get_app_name()}")
print(f"Version:    {apk.get_androidversion_name()}")
print(f"Min SDK:    {apk.get_min_sdk_version()}")
print(f"Target SDK: {apk.get_target_sdk_version()}")

# Dangerous permissions
dangerous_perms = {
    "android.permission.READ_SMS": "SMS theft",
    "android.permission.RECEIVE_SMS": "SMS interception",
    "android.permission.SEND_SMS": "Premium SMS fraud",
    "android.permission.READ_CONTACTS": "Contact harvesting",
    "android.permission.READ_CALL_LOG": "Call log theft",
    "android.permission.RECORD_AUDIO": "Audio surveillance",
    "android.permission.CAMERA": "Camera surveillance",
    "android.permission.ACCESS_FINE_LOCATION": "Location tracking",
    "android.permission.READ_PHONE_STATE": "Device fingerprinting",
    "android.permission.SYSTEM_ALERT_WINDOW": "Overlay attacks",
    "android.permission.BIND_ACCESSIBILITY_SERVICE": "Full device control",
    "android.permission.REQUEST_INSTALL_PACKAGES": "Sideloading apps",
    "android.permission.BIND_DEVICE_ADMIN": "Device admin abuse",
}

print("\nDangerous Permissions:")
for perm in apk.get_permissions():
    if perm in dangerous_perms:
        print(f"  [!] {perm}")
        print(f"      Risk: {dangerous_perms[perm]}")
    elif "android.permission" in perm:
        print(f"  [*] {perm}")

# Components
print("\nActivities:")
for act in apk.get_activities():
    print(f"  {act}")

print("\nServices:")
for svc in apk.get_services():
    print(f"  {svc}")

print("\nReceivers:")
for rcv in apk.get_receivers():
    print(f"  {rcv}")
PYEOF

Step 2: Decompile with JADX

Open the APK in JADX for Java/Kotlin source analysis:

# Open in JADX GUI
jadx-gui malware.apk

# Command-line decompilation for scripted analysis
jadx -d jadx_output/ malware.apk --show-bad-code

# Decompile with all options
jadx -d jadx_output/ malware.apk \
  --deobf \
  --deobf-min 3 \
  --deobf-max 64 \
  --show-bad-code \
  --threads-count 4

# The output directory structure:
# jadx_output/
#   sources/           <- Decompiled Java source code
#     com/malware/app/
#       MainActivity.java
#       C2Service.java
#       SMSReceiver.java
#   resources/         <- Decoded resources (layouts, strings, assets)
#     AndroidManifest.xml
#     res/
#     assets/

Step 3: Identify Malicious Functionality

Search for suspicious code patterns in decompiled sources:

# Search for network communication
grep -rn "HttpURLConnection\|OkHttpClient\|Retrofit\|Volley\|URL(" jadx_output/sources/

# Search for SMS operations
grep -rn "SmsManager\|getDefault().sendTextMessage\|SMS_RECEIVED" jadx_output/sources/

# Search for overlay attack code
grep -rn "SYSTEM_ALERT_WINDOW\|TYPE_APPLICATION_OVERLAY\|WindowManager.LayoutParams" jadx_output/sources/

# Search for accessibility service abuse
grep -rn "AccessibilityService\|onAccessibilityEvent\|performAction" jadx_output/sources/

# Search for data exfiltration

…