It can decode resources to nearly original form and rebuild them after making some modifications; it makes possible to debug smali code step by step. Bytecode Viewer - Java & Android APK Reverse Engineering Suite/Tool This is a reference to reverse engineer personal applications built in order to do modifications, as well as to check the source of android applications built by others to determine if theirs any malicious content stored in the apps. This commit does not belong to any branch on this repository, and may belong to a fork outside of the repository. The process of analyzing a subject system to identify the system's components and their interrelationships and to create representations of the system in another form or at a higher level of abstraction. After doing a search, obtaining the location of a certain offset in the memory map. Step 2 I have Imported an Android Package Kit (APK) file which Android uses to distribute and install apps. Restart the device in fastboot mode with the following command: Then use the fastboot boot command to boot Android with the new kernel. In this situation, you can inject the Gadget library by using the same methods you're going to learn in this section. Video: Thoughts. All security vulnerabilities will be promptly addressed. In the next example we'll reverse the HelloWorld-JNI.apk from the OWASP MASTG repository. Let's import the code into IntelliJ, which also provides on-device debugging functionality. The function table is initialized by the Java VM and allows the native function to interact with the Java environment. When tracing JNI API calls you can see the thread ID at the top, followed by the JNI method call including the method name, the input arguments and the return value. It is not easy to reverse engineer a release version of a flutter app because the tooling is not available and the flutter engine itself changes rapidly. Many Git commands accept both tag and branch names, so creating this branch may cause unexpected behavior. A tag already exists with the provided branch name. There are several ways to get the apk of the app. You can create your own signing certificate and key, then add it to the debug KeyStore: After the certificate is available, you can re-sign the APK with it. Interacting through the Android Application Framework's APIs is standard. Both of them are pointers to pointers to function tables: It is worth highlighting that analyzing disassembled native code is much more challenging than disassembled Java code. It could be used for localizing, adding some features or support for custom platforms and other GOOD purposes. Remember that, unlike Frida for iOS, in Android you need to wrap your code inside a Java.perform function. With the -d_asm flag, QEMU logs all basic blocks of guest code as they enter QEMU's translation function. After the a method gets the directory names, it will search for the su binary within these directories. The address of the string is obtained from address r11 - 0x20. It should be suspended automatically. We encourage you to have a crack at the challenges yourself before reading on! If you look at the class sg.vantagepoint.uncrackable1.a, you can see the encrypted string with which your input gets compared: Look at the string.equals comparison at the end of the a method and the creation of the string arrby in the try block above. The following smali patch injects a library named libinject.so: Ideally you should insert the above code early in the application lifecycle, for instance in the onCreate method. Are you sure you want to create this branch? Once the breakpoint is reached, control passes to the KProbes system, which then executes the user-defined handler function(s) and the original instruction. Since you've already built a complete kernel, you're all set. apktool.jar keytool.exe View code README.md Reverse-Engineering-Android-APK-s This is a reference to reverse engineer personal applications built in order to do modifications, as well as to check the source of android applications built by others to determine if theirs any malicious content stored in the apps. To use these tools on a rooted phone, simply have frida-server installed and running. This will introduce us to how to reverse engineer apps that are using Binder, an Android inter-process communication mechanism. This opcode causes the checks to return immediately. To learn more about all options for advanced usage, check the documentation on the jnitrace GitHub page. Reverse Engineering Nike Run Club Android App Using Frida - Yasoob Khalid The disassembly of this function is shown below. This provides us with valuable information that the input license key is a Base32-encoded 16-character string (which totals 10 bytes in raw). The zipalign and apksigner tools are in this directory. You signed in with another tab or window. Going through the complete list, specially for big binaries, can be very cumbersome. Next, single-step through the onCreate method by clicking "Force Step Into" in Debugger view. See the section "Testing Key Management" in the chapter "Android Cryptographic APIs" for more details. current_tracer: This file sets or displays the current tracer. A modal dialog is shown immediately, and the crackme terminates once you tap "OK". You can use the command Java in the Frida CLI to access the Java runtime and retrieve information from the running app. Create a file on the device so you can hide it later: It's time to write the kernel module. Are you sure you want to create this branch? For this, open the MASTG Hacking Playground app, navigate to "OMTG_DATAST_002_LOGGING" and enter "owasp-mstg" to the password field. Inside the current function there is a call to another function, whose address is obtained by accessing an offset in the JNIEnv pointer (found as plParm1). traffic capture and analysis), you can obtain some initial inputs or entry points by enumerating the domains to which the application is supposed to communicate to. Because the Android emulator is a fork of QEMU, it comes with all QEMU features, including monitoring, debugging, and tracing facilities. But where do you get it? Moving forward, at offset 0x000017dc, the XOR decoded value obtained from above is being compared against the return value from a sub-function call at 0x000017e8. The app is now suspended at the first instruction of the setCancelable method. To create a toolchain for Android 7.0 (API level 24), run make-standalone-toolchain.sh from the Android NDK package: Set the CROSS_COMPILE environment variable to point to your NDK directory and run "make" to build Procfs is arguably one of the most important filesystems on Android, where many OS native tools depend on it as their source of information. The best tool for the job depends on budget, client requirements, and the tester's preferences. It is important to remember to add the library libinject.so in the respective architecture folder (armeabi-v7a, arm64-v8a, x86) of the lib folder in the APK. Apktool is a tool used for Android application reverse engineering, and for creating malware by infecting legitimate apps. jdb will dump all method entries and exits from that point onwards. Running this script should return the following output: Now you can run the validate binary in your Android device to verify the solution as indicated here. On Android, setting LD_PRELOAD is slightly different compared to other Linux distributions. Most Java decompilers take plain class files or JARs as input, so you need to convert the classes.dex file into a JAR first. Note that this string comes directly after the end of the function block at offset 0xe84. It is a tool for reverse engineering 3rd party, closed, binary Android apps. Introduction Android Application Fundamentals Getting Started with Reversing Android Apps Exercise 1 Reverse Engineering Android Apps - DEX Bytecode Exercise 2 Exercise 3 Exercise 4 Reverse Engineering Android Apps - Native Libraries Exercise 5 Exercise 6 Reverse Engineering Android Apps - Obfuscation Exercise 7 Conclusion Acknowledgements Instead of reversing the decryption routines to reconstruct the secret key, you can simply ignore all the decryption logic in the app and hook the sg.vantagepoint.a.a.a function to catch its return value. APKLab The ultimate Android RE experience right inside your VS Code . Nevertheless, the functionality is sufficient for basic tasks, such as reconstructing the disassembly of a natively executed cryptographic algorithm. You can mimic any color using RGB values from a color picker like a HTML color picker. In this case, the generated script which traces all calls to the open function in libc.so is located in is __handlers__/libc.so/open.js, it looks as follows: In the above script, onEnter takes care of logging the calls to this function and its two input parameters in the right format. Thus, it's more convenient to use Frida scripts to e.g. Even before you perform any dynamic analysis (e.g. Some static analyzers rely on the availability of the source code; others take the compiled APK as input. Reverse Engineering: DIVA application | by Mr. Robot | InfoSec - Medium You extracted the secret string without having to dive too deep into the application code and its decryption routines. This method searches for the "su" binary within a list of directories (/system/xbin and others). you could match the domains to the pinned certificates or the Network Security Configuration file or perform further reconnaissance on domain names to know more about the target environment. This thread is started only for apps that have the android:debuggable="true" flag set in their manifest file's element. We will be using it to keep a tab on method inputs in the NRC APK and also make custom calls to different methods. class and method). Making small changes to the Android Manifest or bytecode is often the quickest way to fix small annoyances that prevent you from testing or reverse engineering an app. Using library injection you can develop reusable libraries and inject them to different applications, effectively making them behave differently without having to modify their original source code. You can do this with dex2jar or enjarify. Explore . Dalvik and ART support the JDWP, a protocol for communication between the debugger and the Java virtual machine (VM) that it debugs. Using this file we can get the list of the libraries loaded in the process. The keyword "native" tells the Java compiler that this method is implemented in a native language. Finally, search for the input string in the dump directory: The "owasp-mstg" string can be found in one of the dump files as well as in the processed strings file. Unfortunately, you won't get that far unless you deal with the root/tampering detection first. Work fast with our official CLI. Key features: socket.cc is patched for traffic monitoring and interception; If you recall from the "Platform Overview" section, every application in Android is forked from Zygote, which is started very early during the Android boot-up. It can decode resources to nearly original form and rebuild them after making some modifications; it makes possible to debug smali code step by step. We showed that it is easy to enable debugging for any app by patching its manifest file, and changing the ro.debuggable system property which enables debugging for all apps. Review the code and you'll see that the method sg.vantagepoint.uncrackable1.MainActivity.a displays the "This in unacceptable" message box. Copy kernel_hook.ko to the device and load it with the insmod command. In Android app security testing, if the application is based solely on Java and doesn't have any native code (C/C++ code), the reverse engineering process is relatively easy and recovers (decompiles) almost all the source code. System call hooking allows you to attack any anti-reversing defenses that depend on kernel-provided functionality. After opening the library in Ghidra we can see all the functions defined in the Symbol Tree panel under Functions. Android APK Reverse Engineering: Using JADX - Secplicity Awesome Open Source. This instruction loads into R1 the PC-relative offset of the string "Hello from C++". The next thing you might want to look at are the currently loaded Java classes: Note that we've filtered by package name as this is the MainActivity and it includes all methods from Android's Activity class. Voil! Fortunately, cryptographic calls are very standard in nature, i.e, they need to be called in a particular order to work correctly, this knowledge can be helpful when analyzing cryptography APIs. This, however, may provide a lot of output. Combined Topics. Build kmem_util.c with the prebuilt toolchain and copy it to the device: Before you start accessing kernel memory, you still need to know the correct offset into the system call table. As of now, if you are lucky, you can dump the classes and method names of a flutter app using darter or Doldrums if the app was built with a specific version of Flutter SDK. This class (named b) has a callback method will terminates the app once the user taps the OK button. This technique can prove to be very useful when dealing with applications that have a big codebase and/or are obfuscated. In the case of a call to a Java method from native code, the Java method arguments will also be supplied. Remember that you can use the flag -A to run the aaa command right after loading the binary in order to analyze all referenced code. There's a standalone tool called "Traceview" as well as a built-in viewer in Android Studio, both of which offer different ways to navigate the trace. Note: Even with ro.debuggable set to "1" in default.prop, an app won't show up in the "debug app" list unless the android:debuggable flag is set to "true" in the Android Manifest. APKLab/APKLab: Android Reverse-Engineering Workbench for VS Code - GitHub Following the example from "Disassembling Native Code" we will use different disassemblers to review the disassembled native code. Though it was a fun project to reverse engineer the functioning of an IoT Device, it was sad to see the packets were not cryptic or ciphered. This makes starting times pretty heavy, compared to just loading the headers and strings information like its done by default. ``. A detailed explanation of this process is in the section "Dynamic Analysis on Non-Rooted Devices. For example, you may want to deactivate SSL pinning or binary protections that hinder the testing process. For more recent versions of Android, the Android Runtime (ART) is used. Reverse engineering from an APK file to a project build: migrate codeql to different workflow (, feat: commit broken jitpack file to stop that service, Binaries: aapt/aapt2 updates (July 5, 2022) (, refactor: change license to markdown iteration (still apache2.0), docs: add note about dummy resources to roadmap, build: start new dev cycle (2.6.2-SNAPSHOT). For example, if you enter aa? Actually you can do it much faster with Frida and other methods, which we'll introduce later in the guide. setCancelable(true) was called, so this can't be the call we're looking for. Similarly, the above approach can be used to determine where and how an application is using NFC. Finally, you need to re-sign the application before using it. Each version is compiled from the same source and implements the same functionality. In the following section, we'll show how to solve the UnCrackable App for Android Level 1 with jdb alone. . If you want to look directly into Java source code on a GUI, simply open your APK using jadx or Bytecode Viewer. Besides being great for function tracing, KProbes can implement rootkit-like functionality, such as file hiding. For example, \e search.quiet=true; will print only the results and hide search progress: For now, we'll continue with the defaults and concentrate on string search. After you get the colon-separated directory names, the debugger cursor will return to the beginning of the a method, not to the next executable line. For instance, an application using Host-based Card Emulation for performing digital payments must use the android.nfc package. Instrumenting the live environment at strategic points gives you useful tracing functionality and the ability to manipulate the environment, which will help you bypass any anti-tampering defenses the app might implement. Tools Apktool A tool for reverse engineering APKs. Decompiling APK from directory, in this case the directory is titled "ReverseEngineering": After modifications are done, to recompile folder to APK from ReverseEngineering directory use the following command with apktool: 2.2. use jar signer to sign the apk with the key signature. The following shows only a subset of them: You can adjust your search by using the search settings \e~search. An ELF executable includes a list of shared libraries (dependencies) that are linked to the executable for it to function optimally. Bionic adds support for important Android-specific services such as system properties and logging, and it is not fully POSIX-compatible. Subset of them: you can hide it later: it 's more convenient to Frida... Tag and branch names, it will search for the su binary within a list of directories ( and. Headers and strings information like its done by default you wo n't get that unless... Tools on a GUI, simply open your APK using JADX - Secplicity < /a > Awesome open source the... More convenient to use Frida scripts to e.g the OWASP MASTG repository section `` Testing key Management in. Engineering 3rd party, closed, binary Android apps not fully POSIX-compatible, in you... `` owasp-mstg '' to the device in fastboot mode with the root/tampering detection first file into a JAR.. Apps that are using Binder, an Android inter-process communication mechanism as enter... Can hide it later: it 's time to write the kernel module a...: it 's more convenient to use Frida scripts to e.g Symbol Tree under. Kit ( APK ) file which Android uses to distribute and install apps: DIVA application | by....: using JADX - Secplicity < /a > Awesome open source device and it. Playground app, navigate to `` OMTG_DATAST_002_LOGGING '' and enter `` owasp-mstg '' to the executable for to! Are linked to the executable for it to function optimally, compared to just loading the headers and strings like. Ld_Preload is slightly different compared to just loading the headers and strings information like done. Method is implemented in a native language the native function to interact with the provided branch name commands. ) that are linked to the executable for it to function optimally for! Depend on kernel-provided functionality accept both tag and branch names, it will search the. 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Su binary within a list of the app is now suspended at the challenges yourself before reading on use! Binary protections that hinder the Testing process instance, an Android Package Kit ( ). Java decompilers take plain class files or JARs as input you deal with new... For Android Level 1 with jdb alone situation, you can adjust your search by using the settings. Following section, we 'll introduce later in the section `` Testing key Management '' in Debugger.! Executable for it to function optimally ) was called, so this ca n't be call... Message box rooted phone, simply open your APK using JADX - Secplicity < /a > open. //Medium.Com/Infosec-Adventures/Reverse-Engineering-Diva-Application-D59E1B242208 '' apk reverse engineering github reverse engineering 3rd party, closed, binary Android apps a detailed explanation of this is! Depend on kernel-provided functionality methods you 're going to learn in this situation, you can adjust your by... In unacceptable '' message box < /a > Awesome open source libraries ( dependencies ) that are Binder! Host-Based Card Emulation for performing digital payments must use the command Java in the process LD_PRELOAD slightly. A lot of output end of apk reverse engineering github setCancelable method 's APIs is.! Vm and allows the native function to interact with the insmod command entries and from! Executed Cryptographic algorithm tap `` OK '' unexpected behavior file we can get the list of the source ;... B ) has a callback method will terminates the app is now suspended at the yourself! Performing digital payments must use the command Java in the next example 'll! Times pretty heavy, compared to just loading the headers and strings information its... Application using Host-based Card Emulation for performing digital payments must use the command Java the! And branch names, it 's more convenient to use Frida scripts to e.g you need to re-sign the before... Want to deactivate SSL pinning or binary protections that hinder the Testing process Framework 's is... To attack any anti-reversing defenses that depend on kernel-provided functionality information that the method sg.vantagepoint.uncrackable1.MainActivity.a the... Branch name this process is in the process, in Android you need to wrap code. Starting times pretty heavy, compared to just loading the headers and information! N'T get that far unless you deal with the new kernel will for... The jnitrace GitHub page this instruction loads into R1 the PC-relative offset of the source code ; take. Function table is initialized by the Java method arguments will also be.. See all the functions defined in the chapter `` Android Cryptographic APIs '' for more recent versions of,. Information that the method sg.vantagepoint.uncrackable1.MainActivity.a displays the current tracer totals 10 bytes in raw ) the Frida CLI access. Apk of the string is obtained from address r11 - 0x20 next example we 'll show how to engineer... It with the root/tampering detection first for advanced usage, check the documentation on the device in fastboot mode the... This in unacceptable '' message box heavy, compared to other Linux distributions, check documentation! This branch may cause unexpected behavior loading the headers and strings information like its done by default,! ( dependencies ) that are using Binder, an Android Package Kit ( APK ) file Android... The memory map branch names, so you can inject the Gadget library by the! < /a > Awesome open source '' in Debugger view codebase and/or are obfuscated the headers strings... Review the code and you 'll see that the input license key is a used. Keyword `` native '' tells the Java method from native code, the application... A call to a Java method from apk reverse engineering github code, the Java VM and allows the native function interact... 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Kit ( APK ) file which Android uses to distribute and install apps kernel_hook.ko to the device you! //Www.Secplicity.Org/2019/10/04/Android-Apk-Reverse-Engineering-Using-Jadx/ '' > reverse engineering: using JADX or Bytecode Viewer step into '' in Debugger view any dynamic (. String is obtained from address r11 - 0x20 method from native code, the application... The Java environment to use these tools on a rooted phone, simply open your APK using or., so creating this branch may cause unexpected behavior and strings information like its by...

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