ingehack2k25 - reverse/mjsc

MJSC CTF Challenge Write-up

Challenge: reverse/mjsc
Event: IngeHack 2k25
Author: 4ymen
Points: 469
Solves: 4
Difficulty: Medium
Original Challenge Author: itskarudo

Challenge Information

• Category: Reverse Engineering
• Type: Web/JavaScript
• Flag: ingehack{i_hate_js_rev_chals_they_never_have_a_new_idea}

Initial Analysis

The challenge presented us with a web application that needed to be analyzed. The initial reconnaissance showed:

1. Web interface requiring input validation
2. Heavy use of JavaScript for validation
3. Obfuscated code to hide the validation logic

Technical Environment

Platform: Web
Primary Language: JavaScript
Key Components:
  - React Application
  - Obfuscated JavaScript
  - Client-side validation

Investigation Process

1. Source Code Retrieval

   Read More…

ingehack2k25 - reverse/dados

• Write-Up Author : 4ymen

• Flag: ingehack{security_by_obscurity}

Challenge Description:

infinite luck in exchange for a flag

dados.apk

title: "Reverse Engineering Challenge "
difficulty: Easy
category: Reverse Engineering
platform: Android
tools: ["apktool", "smali", "Frida", "adb"]
author : "godsword"
date: "2025-02-23"
tags: ["Reverse Engineering", "Android", "Frida", "Smali", "CTF"]
---

Write up

Step 1: Identifying the Main Activity

After decompiling dados.apk, I checked AndroidManifest.xml to find the app’s entry point. The <activity> tag with <intent-filter> containing android.intent.action.MAIN and android.intent.category.LAUNCHER revealed that the main activity is:

smileyCTF2025 :

rev/DNA

Flag : .;,;.{we_ought_to_start_storing_our_data_as_dna_instead}

Description

deoxy ribo nucleic acid deoxy meaning without oxygen ribo meaning the 5-carbon sugar backbone nucleic meaning of the nucleus acid meaning proton donor

Solution

Initial Recon

We start by looking at the challenge directory:

➜  dna ls
main.cpython-310.pyc  vm.dna
➜  dna 

We can see that this is a virtual machine challenge, and the Python code has been compiled with Python 3.10 into a .pyc file ,Before diving into the challenge, let’s take a moment to understand what a virtual machine (VM) is.