Hackthebox - Introduction to Android Exploitation - Track

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  • For this track you will need a setup for Android App Hacking. You can see how to set this up here

Challenge - Pinned

  • Here is the readme

1. Install this application in an API Level 29 or earlier (i.e. Android 10.0 (Google APIs)).
  • For this challenge we need to bypass certificate pinning.

  • Take frida server from here

  • unxz frida-server-version-android-x86.xz to decompress the file

  • mkdir frida-on-venv In my opt folder, I created a new folder for frida.

  • sudo python3 -m venv frida Create the virtual env for frida

  • source frida/bin/activate Activate the env

  • pip3 install frida-tools Install Frida

  • Install the apk file in your virtual machine (you can drag and drop it)

  • Launch it and keep it on screen

  • adb push frida-server-16.0.8-android-x86 /data/local/tmp/frida-server

  • adb root (it should be already rooted but just for sanity)

  • adb shell "chmod 755 /data/local/tmp/frida-server" so that you can launch it ;)

  • In another terminal tab adb shell to drop in your android shell

  • su

  • /data/local/tmp/frida-server & to launch frida-server

  • frida-ps -U -ai from your host (will list the process) you should see pinned in the list

  • Take this script wget https://raw.githubusercontent.com/httptoolkit/frida-android-unpinning/main/frida-script.js

  • Then you just need to run frida -U -l ./frida-script.js -f com.example.pinned

  • Now we should be able to intercept the traffic and actually see it in Burp (frida server should still be running for this process)

  • Click login in your screen

  • And we got the flag from Burp

Challenge - Manager

  • Here is the readme

  • We need to exactly the same process as we did for Pinned and bypass cert pining.

  • For it to work I used Android 7 API 25

  • You should now be able to intercept the traffic.

  • Connect to the instance you started

  • Create an account

  • When I logged in with my account I saw there was this role parameter that looked interesting

  • I tried to register a member with an admin role but without success. However I tried admin and got this error Username already taken!

  • So we know that there is a user admin.

  • And after some exploration I saw that to change the password it just need a username and a password.

  • So why not try to change the password for the admin user

  • It works!

  • We can now login as admin and we get the flag

Challenge Anchored

  • Here is the readme

1. Install this application in an API Level 29 or earlier (i.e. Android 10.0 (Google Play)).

2. Install this application in a non-rooted device (i.e. In Android Studio AVD Manager select an image that includes (Google Play)).
  • So for the other challenged I used Genymotion, but for this one I am going to use android studio (with burp and all the necessary setup)

  • It seems like we will need to bypass cert pining without root rights

  • So we have a non-rooted Android 10 VM

  • In order to do this we need objection and objection needs clean version of apktool (not the one that has -dirty in the end)

$ apktool --version
  • Now we need to patch the apk objection patchapk -s ~/Documents/kali-shared/hackthebox/Anchored/Anchored/Anchored.apk

$ objection patchapk -s Anchored.apk 
No architecture specified. Determining it using `adb`...
Detected target device architecture as: x86
Using latest Github gadget version: 16.0.8
Patcher will be using Gadget version: 16.0.8
Detected apktool version as: 2.7.0
Running apktool empty-framework-dir...
I: Removing 1.apk framework file...
Unpacking Anchored.apk
App already has android.permission.INTERNET
Target class not specified, searching for launchable activity instead...
Reading smali from: /tmp/tmpfr2zcaji.apktemp/smali/com/example/anchored/MainActivity.smali
Injecting into an existing constructor
Injecting loadLibrary call at line: 18
Attempting to fix the constructors .locals count
Current locals value is 1, updating to 2:
Writing patched smali back to: /tmp/tmpfr2zcaji.apktemp/smali/com/example/anchored/MainActivity.smali
Copying Frida gadget to libs path...
Rebuilding the APK with the frida-gadget loaded...
Built new APK with injected loadLibrary and frida-gadget
Performing zipalign
Zipalign completed
Signing new APK.
Signed the new APK
Copying final apk from /tmp/tmpfr2zcaji.apktemp.aligned.objection.apk to Anchored.objection.apk in current directory...
Cleaning up temp files
  • After this we get a version of the apk with objection in the name Anchored.objection.apk

  • We can install it in our VM adb install Anchored.objection.apk

  • We can lauch it. The app will be frozen (it's normal)

  • objection explore

  • And now we have to disable ssl pinning android sslpinning disable

  • It will launch the screen and you will see the traffic in burp

  • Here is the app we can try to enter a random email and request access

  • And we get the flag (do not forget to put it in HTB{} before submitting it)

Challenge APKrypt

  • Here is the readme

1. Install this application in an API Level 29 or earlier (i.e. Android 10.0 (Google APIs)).
  • Let's have a look at the code ./jadx-gui

  • Having a look at the java code, we can see that it takes a string it md5 it and compares it to this md5 hash 735c3628699822c4c1c09219f317a8e9

  • Here is the snippet from jadx-gui

  • Let's see if we can crack it. We are not successful with crackstation or hashcat.

  • We know we could modify the smali code. Maybe we could change the hash to a custom hash like my name in md5 or test or anything.

  • We could also modify the condition

  • So yes, with access to the code and possibility to modify it we can do multiple things

  • So let decompile the apk with apktool apktool d ../APKrypt.apk

  • We get these files

  • Let's open the folder in a code editor (I use VSCodium see my page about it here) and look for the md5 hash 735c3628699822c4c1c09219f317a8e9. We find it in /APKrypt/smali/com/example/apkrypt/MainActivity$1.smali

  • So let's change the md5 hash

$ echo -n "test" | md5sum
098f6bcd4621d373cade4e832627b4f6  -
  • Spoiler alert: this does not work. Let's change the condition instead

  • We need to change this if-eqz p1, :cond_0 to this if-nez p1, :cond_0

  • Let's save it and recompile it

    • apktool b APKrypt/

  • Now we need to sign or we will not be able to debug it. We can use this command that we found in this thread of stack overflow to generate the key (it will ask for a password you will need it to sign the apk)

    • keytool -genkey -v -keystore my-release-key.keystore -alias alias_name -keyalg RSA -keysize 2048 -validity 10000

    • So for me keytool -genkey -v -keystore my-release-key.keystore -alias apkrypt -keyalg RSA -keysize 2048 -validity 10000

  • Now that we have the key we can sign the apk with jarsigner see this thread on stackoverflow for a command jarsigner -verbose -sigalg SHA1withRSA -digestalg SHA1 -keystore my-release-key.keystore my_application.apk alias_name

    • In my case jarsigner -verbose -sigalg SHA1withRSA -digestalg SHA1 -keystore my-release-key.keystore APKrypt.apk apkrypt

  • Let's open our new file with Android Studio to debug it

  • In android studio we go to file>profile and debug apk

  • And with the modified condition it works so even if what we type is not equal to the hash we will get the code

  • This is also our flag HTB{3nj0y_y0ur_v1p_subscr1pt1on}

Challenge - SeeTheSharpFlag

Writeup will be public as soon as this challenge is retired

Box - Explore

Challenge - SAW

Writeup will be public as soon as this challenge is retired

Challenge - Don't Overreact

Writeup will be public as soon as this challenge is retired

Challenge - APKey

Writeup will be public as soon as this challenge is retired

Full track achieved

  • And we finished the track!

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