Using found.solver.eval you can ask the solver questions like "given the output of this sequence of operations (the current state in found), what must the input (at addr) have been?"). It may not look like much, but its Java method tracer is one of the most awesome tools you can have in your arsenal, and it is indispensable for analyzing obfuscated bytecode. Join the Reverse Engineering Discord! Active, moderated - reddit I have the following active cyber-related certifications: eJPT, eWPT, eCPPTv2, eWPTXv2, CRTP, OSWP and OSCP Only 20$/365 Days VIP eLearnSecurity Certified Professional Penetration Tester (eCPPTv2) eLearnSecurity Certified Penetration Tester eXtreme (eCPTX) eLearnSecurity Exploit Development (eCXD) > eLearnSecurity Certified Reverse Engineer (eCRE. This time, we will input a string and see if we can find it in the memory dump. Note that for bigger binaries, starting directly with the flag -A might be very time consuming as well as unnecessary. A FREE comprehensive reverse engineering tutorial covering x86, x64, 32-bit ARM & 64-bit ARM architectures. Setting ro.secure to "0" causes adbd to run as root. Each DEX file contains a list of string identifiers (strings_ids), which contains all the string identifiers used in the binary whenever a string is referred, including internal naming (e.g, type descriptors) or constant objects referred by the code (e.g hardcoded strings). 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. In the real world, especially when reversing malware or more complex apps, pure static analysis is very difficult. Working on real devices has advantages, especially for interactive, debugger-supported static/dynamic analysis. It also makes working with an app easier because of the project like file structure and automation of some repetitive tasks like building apk, etc. Reverse Engineering: DIVA application | by Mr. Robot | InfoSec - Medium Create a Makefile with the following content: Run make to compile the code, which should create the file kernel_hook.ko. Reverse Engineering Android Applications - Penetration Testing Lab The target crackme is a simple Android License Validator executable. setCancelable(true) was called, so this can't be the call we're looking for. Unfortunately, this isn't possible at this point in the execution because libnative-lib.so isn't yet mapped into process memory, it's loaded dynamically during runtime. This is where user input is compared with the secret string. Remember to always type ? You can then deactivate this protection and make many other useful customizations that simplify reverse engineering. APK Decompiler for Windows, Mac or Linux 4. Reverse Engineering and Debugging 3rd Party Android APKs Recently, I had compiled an ultimate list of 47 best APK decompilers on my website. available_tracers: This file lists the available tracers compiled into the kernel. This Information is often used for other techniques, such as method hooking. Write a Frida hook to change how that code works. How to run. If you are looking for the Apktool website. This pointer points to a function table: an array of even more pointers, each of which points to a JNI interface function (is your head spinning yet?). Most of the apps you might encounter connect to remote endpoints. At the lowest level, however, many important functions (such as allocating memory and accessing files) are translated into old-school Linux system calls. With Ghidra, strings can be obtained by simply loading the DEX file and selecting Window -> Defined strings in the menu. Android App Reverse Engineering 101 | Learn to reverse engineer Android Put this file wherever you want (in my case ~/Dev) and add an alias to it in your .bashrc for ease of use: alias apktool= 'java -jar ~/Dev/apktool_2.4.1.jar' 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. If nothing happens, download GitHub Desktop and try again. In . In our example, a search for "X509TrustManager" returns one class that implements a custom TrustManager. Enter "java" and hit enter. Finally the resource files in the APK can be. In this section we can look into the decompilation of the function. 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. Conveniently, the stock Android kernel on both Lollipop and Marshmallow include ftrace functionality. You should get an output similar to the following: The hooked function outputted the decrypted string. There are three user defined functions: FUN_001004d0, FUN_0010051c, and Java_sg_vantagepoint_helloworldjni_MainActivity_stringFromJNI. This skipping makes following the code flow crucial to debugging decompiled applications. Create a file called kernel_hook.c with the following code: To build the kernel module, you need the kernel sources and a working toolchain. The most relevant fields for us, similar to the previous output, are following: The file /proc//maps contains the currently mapped memory regions and their access permissions. Use the following command: Once in the r2frida session, all commands start with \. Next, the current value of PC is added to R1, resulting in the absolute address of the static string "Hello from C++" (PC + offset). Step into the System.getenv method with the "Force Step Into" feature. Notes: Application does not consume system proxy configuration -> Solution: Modify /etc/hosts to redirect inbound requests ( Burp) On Android the AOT Compilation option requires an Enterprise license or higher, is available only when the project is configured for Release mode, and it is disabled by default. It can be achieved via runtime instrumentation and allows to perform tasks such as: As you can see, these passive tasks help us collect information. An example for tracing libc's open function using frida-trace is demonstrated below, where -U connects to the USB device and -i specifies the function to be included in the trace. Clicking any of the methods in the profile panel highlights the selected method in the timeline panel. Reverse Engineering Android Apps - Native Libraries Android applications can contain compiled, native libraries. We will be using it to keep a tab on method inputs in the NRC APK and also make custom calls to different methods. With objection it is possible to dump all memory of the running process on the device by using the command memory dump all. sg.vantagepoint.a.a (again, everything is called a) along with something that looks suspiciously like a hex-encoded encryption key (16 hex bytes = 128bit, a common key length). On Android, which is a Linux based OS, you can load an additional library by setting the LD_PRELOAD environment variable. Reverse Engineer Your Favorite Android App - Medium In the following example we'll be using UnCrackable App for Android Level 1. Open ThaiCamera.apk in the jadx GUI. Thanks to tools like objection, you can patch the app in order to test it like if you were on a rooted device (but of course being jailed to that one app). See r2frida's help on the search command (\/?) Method hooking with an Xposed module is one way to do this (see "Android Basic Security Testing" for more details on Xposed installation and basics). Android's implementation of JDWP also includes hooks for supporting extra features implemented by the Dalvik Debug Monitor Server (DDMS). You can use the command Java in the Frida CLI to access the Java runtime and retrieve information from the running app. 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. Next, run Fridump: Tip: Enable verbosity by including the flag -v if you want to see more details, e.g. Bytecode Viewer - Java & Android APK Reverse Engineering Suite/Tool You can find the function prototypes for all system calls in the kernel header file arch/arm/include/asm/unistd.h. This method searches for the "su" binary within a list of directories (/system/xbin and others). You may do so by running the \dm. In this section, we will solve a simple Android crackme by using the Angr binary analysis framework as our symbolic execution engine. Click here. Most of the time, the JavaScript code in this file is minified. Conclusion 5. However, there are also a few Android-specific challenges. Thus, it is recommended to start with keyword-based searching and go through the list only when keyword search does not help. Android Anti-Reversing Defenses - OWASP MASTG - GitBook Of course, the only way to really learn it is hands-on experience: build your own projects in Android Studio, observe how your code gets translated into bytecode and native code, and try to crack our challenges. To get around this, build your own kernel. Member-only Reverse engineering and modifying an Android game (.apk) CTF Recently I solved a CTF style challenge where the user was given an .apk file with the goal to find the flag. Find the boot partition: Next, extract the ramdisk and information about the structure of the boot image. With the device connected via USB, you can forward this port to a local port on the host with the abd forward command: You'll now use the prebuilt version of gdb included in the NDK toolchain. GitHub Instantly share code, notes, and snippets. However, there's a downside: as strace depends on the ptrace system call to attach to the target process, once anti-debugging measures become active it will stop working. Also note the "This is unacceptable" message from the first method of the class, private void a. Reverse engineering is the process of reconstructing the semantics of a compiled program's source code. Addressing relative to the program counter allows the code to run independently of its position in memory. Observing and manipulating an app during runtime makes it much, much easier to decipher its behavior. This may appear magical at first, but a careful analysis of the function at 0x00001760 holds the clue, as it determines if the given input string is a valid license key or not. If you have built a project in Android Studio before, the IDE has already created a debug keystore and certificate in $HOME/.android/debug.keystore. Patching APKs to load frida-gadget.so on start. The results generated by static analyzers can otherwise be overwhelming, and your efforts can be counterproductive if you must manually investigate a large report. Show References to in Ghidra or Find Usage in jadx. The openat system call is defined in unistd.h, which is in the kernel sources: The final piece of the puzzle is the address of your replacement-openat. Echoing "0" will prevent further writes into the ring buffer. Note that this string comes directly after the end of the function block at offset 0xe84. In the next example we'll reverse the HelloWorld-JNI.apk from the OWASP MASTG repository. Before moving ahead, pay attention to the first parameter passed to the current JNI function. Here is the complete script that prevents exiting on root and intercepts the decryption of the secret string: After running the script in Frida and seeing the "[*] sg.vantagepoint.a.a.a modified" message in the console, enter a random value for "secret string" and press verify. For this, open the MASTG Hacking Playground app, navigate to "OMTG_DATAST_002_LOGGING" and enter "owasp-mstg" to the password field. Identify where the code should be patched in the temporary file and implement the changes. Procfs provides a directory-based view of a process running on the system, providing detailed information about the process itself, its threads, and other system-wide diagnostics. The following shows only a subset of them: You can adjust your search by using the search settings \e~search. Jprobes and Kretprobes are other KProbes-based probe types that allow hooking of function entries and exits. You'll also need the right toolset to deal with both the bytecode running on the Java virtual machine and the native code. apk.sh - a Bash script that makes reverse engineering Android apps maddiestone/AndroidAppRE: Android App Reverse Engineering Workshop - GitHub Android's openness makes it a favorable environment for reverse engineers. Reverse engineering Android APK's. A collection of hacking / penetration testing resources to make you better! To do that you have to perform one additional step: patch the APK to include the Frida gadget library. In order to use frida-trace, a Frida server should be running on the device. Again, you can get this address from /proc/kallsyms. * Written to run on Java 7, supports Java 8. 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. They can still be reverse engineered, but the process is not automated and requires knowledge of low-level details. For instance, we can easily filter it by PID: netstat output is clearly more user friendly than reading /proc//net. Binary analysis frameworks typically use a technique called symbolic execution, which allow to determine the conditions necessary to reach a specific target. Now you can set breakpoints and attach to the app process with the "Attach Debugger" toolbar button. DDMS also offers a convenient heap dump button that will dump the Java heap of a process to a .hprof file. Elearnsecurity exploit development exam If the React Native framework has been used for developing then the main application code is located in the file assets/index.android.bundle. Fortunately, Java decompilers generally handle Android bytecode well. armeabi: ABI is for ARM-based CPUs that support at least the ARMv5TE instruction set. Once you have a JAR file, you can use any free decompiler to produce Java code. This list can be modified to insert an additional library to be injected into the process. Step 2 I have Imported an Android Package Kit (APK) file which Android uses to distribute and install apps. Before booting into the new kernel, make a copy of your device's original boot image. android - Reverse engineering app modifying the apk to accept the Android App Reverse Engineering 101 | Learn to reverse engineer Android It contains an important configuration file, default.prop, that defines some basic system properties. An application can be assessed by side-loading it, re-packaging it, or by simply attacking the installed version. When testing an app, process exploration can provide the tester with deep insights into the app process memory. reverse-engineering GitHub Topics GitHub A well-known use case of this technique is loading the Frida gadget to an application, specially while working on a non-rooted device (this is what objection patchapk basically does). When you're analyzing a more complex app, however, it can get quite annoying. The only problem is that you're already too late to debug the JNI function StringFromJNI; it only runs once, at startup. 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. There are many of these: open, openat, access, accessat, facessat, stat, fstat, etc. Another important restriction is that line breakpoints won't work because the release bytecode doesn't contain line information. Which are empty in this case. You can edit the onLeave event to print the return values as shown above. M9: Reverse Engineering - Kotlin SCP Reverse engineering & modifying Android apps with JADX & Frida You can't intercept HTTPS traffic with a proxy because the app employs SSL pinning. You can even directly see the size and the path to that binary in the Android file system. Once you have created the project, expand the "1: Project" view on the left and navigate to the folder app/src/main/java. Next, the endness parameter in the script specifies that the data is stored in "little-endian" fashion, which is the case for almost all of the Android devices. The "Hello World" text view is populated in the onCreate method: Note the declaration of public native String stringFromJNI at the bottom. Many command line tools are not shipped with the Android firmware to reduce the size, but can be easily installed on a rooted device using BusyBox. The easiest way to run CFR is through apkx, which also packages dex2jar and automates extraction, conversion, and decompilation. See the man page for more options. Capstone disassembly/disassembler framework: Core (Arm, Arm64, BPF, EVM, M68K, M680X, MOS65xx, Mips, PPC, RISCV, Sparc, SystemZ, TMS320C64x, Web Assembly, X86, X86_64, XCore) + bindings. Reverse Engineer an APK in KALI - YouTube Take a closer look at the latter part of the script where the final solution string is being retrieved. Since you've already built a complete kernel, you're all set. Therefore, a good stating point for NFC API analysis would be to consult the Android Developer Documentation to get some ideas and start searching for critical functions such as processCommandApdu from the android.nfc.cardemulation.HostApduService class. You can solve this problem by activating the "Wait for Debugger" option. This prevents writing to kernel memory regions marked as read-only, so any attempt to patch kernel code or the system call table result in a segmentation fault and reboot. arm64-v8a: ABI for ARMv8-based CPUs that support AArch64, the new 64-bit ARM architecture. Copy kernel_hook.ko to the device and load it with the insmod command. This interrupt calls the vector_swi kernel function, which then uses the system call number as an offset into a table (known as sys_call_table on Android) of function pointers. So far, you've been using static analysis techniques without running the target apps. they are searched first by the loader while resolving the symbols, effectively overriding the original ones. Use Git or checkout with SVN using the web URL. in conjunction with regular expressions) to further filter and analyze the results. Many Git commands accept both tag and branch names, so creating this branch may cause unexpected behavior. Tracing functions by address when no function name symbols are available (stripped binaries), e.g. arrby is the return value of the function sg.vantagepoint.a.a.a. You can use its adb jdwp command to list the process IDs of all debuggable processes running on the connected device (i.e., processes hosting a JDWP transport). Thus, it's more convenient to use Frida scripts to e.g. In this section we've just slightly touched the surface, please refer to the section "Basic Network Monitoring/Sniffing" in the "Android Basic Security Testing" chapter and also check the test cases in the "Android Network Communication" chapter. The UnCrackable App for Android Level 1 is not stupid: it notices that it has been run in debuggable mode and reacts by shutting down. The experience won't be perfect, it's not the original source code after all, so you won't be able to set line breakpoints and things will sometimes simply not work correctly. With Frida, you can prevent the app from exiting by hooking the MainActivity.a method or the callback inside it. As we will soon observe, the key validation logic in the crackme is implemented in native code. In the case of a call to a Java method from native code, the Java method arguments will also be supplied. You can easily repackage an app by doing the following: Note that the Android Studio build tools directory must be in the path. It could be used for localizing, adding some features or support for custom platforms and other GOOD purposes. Starting QEMU with the -d command line flag will cause it to dump the blocks of guest code, micro operations, or host instructions being executed. Once you're done, click the same button to stop the recording. You can simply dump this list using tools such as Ghidra (GUI based) or Dextra (CLI based). You signed in with another tab or window. It contains prebuilt versions of gdbserver for various architectures. When you open the application in jadx, you will see the following. You can start by searching for "Hello" and see what r2frida finds: Now you'd like to know where are these addresses actually. Please to the iOS chapter for more examples on Angr usage. Determining the presence of these libraries in an application can give us valuable information about its nature. A JDWP debugger allows you to step through Java code, set breakpoints on Java methods, and inspect and modify local and instance variables. 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. For example, when you only want to modify the Android Manifest and repack immediately. Language: All Let's Reverse Engineer an Android App! - Yasoob Khalid This makes starting times pretty heavy, compared to just loading the headers and strings information like its done by default. This commit does not belong to any branch on this repository, and may belong to a fork outside of the repository. If you discover a security vulnerability within Apktool, please send an e-mail to Connor Tumbleson at connor.tumbleson(at)gmail.com. If you have any problems, a first step would be to enable the debug flag -d when running objection or, if that doesn't help, file an issue in objection's GitHub. Our objective is to set a breakpoint at the first instruction of the native function Java_sg_vantagepoint_helloworldjni_MainActivity_stringFromJNI before resuming the app. Explore . Changing this file can make the Android environment easier to reverse engineer. Instead, we just tell radare2 to analyze that one function by using the analyze function af command. "Ida View-A" should now show the disassembly of the function. Finally jnitrace will attempt to use the Frida backtracing library to show where the JNI call was made from. Note that many of the decompiled packages, classes, and methods have weird one-letter names; this is because the bytecode has been "minified" with ProGuard at build time. TOOLS USED:https://ibotpeaches.github.io/Apktool/https://github.com/pxb1988/dex2jarhttps://github.com/skylot/jadxhttps://developer.android.com/studiohttps://. Apktool is one of the most importa. It also makes working with an app easier because of the project like file structure and automation of some repetitive tasks like building apk, etc An Information Security Reference That Doesn't Suck; You signed in with another tab or window. Let's assume you're testing an app that's stubbornly quitting on your rooted device. Runtime Instrumentation encompasses adding hooks and runtime patches to observe the app's behavior. Unlike the original, the new version of a just writes console output and doesn't exit the app. * Quickly decompile classes using JD-Core. In ARMv7, R11 is called fp (function pointer), therefore R11 - 0x20 is equivalent to fp-0x20: var int32_t var_20h @ fp-0x20. Advanced Reverse Engineering on Android (2016) -. After you choose the app from the list, the debugger will attach to the app process and you'll reach the breakpoint that was set on the onCreate method. In mobile application security however, the term loosely refers to all kinds of runtime manipulation, including overriding methods to change behavior. Once you've unpacked and disassembled the APK, it's time to find the certificate pinning checks in the Smali source code. \is libnative-lib.so. For example, if a block is repeatedly executed in a loop, only the first iteration will be printed to the log. We'll keep using the HelloWorld JNI app, open a session with r2frida r2 frida://usb//sg.vantagepoint.helloworldjni and you can start by displaying the target binary information by using the \i command: Search all symbols of a certain module with \is , e.g. The remaining anti-tampering and anti-debugging controls can be defeated in similar ways so that you can finally reach the secret string verification functionality. In the disassembly above, you can see how the input string to the function (in register R0) is stored into a local stack variable 0x0000176c str r0, [var_20h]. It describes the technical processes for verifying the controls listed in the OWASP Mobile Application Security Verification Standard (MASVS). Sony's Xperia series is also known for its openness. Fortunately, Android's "Developer options" contain the useful "Wait for Debugger" feature, which allows you to automatically suspend an app doing startup until a JDWP debugger connects. To reverse engineer an app and hook some behaviour, there's a few core steps you need to work through: Download a copy of the app on your computer. apktool allows you to reassemble the package, which is useful for patching the app or applying changes to e.g. Setting up a project in an IDE with the decompiled sources is a neat trick that allows you to set method breakpoints directly in the source code. Note: If you experience JRE compatibility issues with apksigner, you can use jarsigner instead. It allows you to inject scripts in native applications and check out what they are doing under the hood. You can bypass this with a little runtime tampering. The Android Studio user guide contains more information about Traceview. If you want to inject your own Frida script, it should either disable the AlertDialog entirely or change the behavior of the onClick method so the app does not exit when you click "OK". It monitors the interaction between processes and the kernel, being a very convenient way to monitor system calls. In this case, we will initialize the state with the first instruction of the serial validation function. These functions are available to normal processes via the system call interface. This extracts the source code into the HelloWord-JNI/src directory. 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. listing classes, tracing method calls, monitoring accessed files, monitoring network access, obtaining direct memory access). Android App Reverse Engineering 101 | Learn to reverse engineer Android Reverse Engineering | Watch Dogs | Security Analysis of Android A detailed explanation of this process is in the section "Dynamic Analysis on Non-Rooted Devices. Discussing all the instructions in the function is beyond the scope of this chapter, instead we will discuss only the important points needed for the analysis. Run it on the APK and you should find the decompiled sources in the directory Uncrackable-Level1/src. GitHub - iBotPeaches/Apktool: A tool for reverse engineering Android

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