Union CTF 2021 - Human server [crypto]

• Competition: Union CTF 2021
• Challenge Name: Human server
• Type: Crypto
• Points: 100 pts
• Description:

  Ever since everyone left WhatsApp, we’ve been overwhelmed by new users. We’ve teamed up with UnionCTF to get some humans working while our servers take a break. You’ll be helping our users send flags to each other, but as we’ve ensured messages are E2E encrypted with state-of-the-art military-grade encryption, their messages will be private. Our customers have nothing to worry about. nc 134.122.111.232 54321 Author: Jack & hyperreality

DiceGang CTF 2021 - Dice is you [rev]

• Competition: DiceCTF 2021
• Challenge Name: Dice is you
• Type: Reversing
• Points: 251 pts
• Description:

  DICE IS YOU

  Controls:

  wasd/arrows: movement space: advance a tick without moving q: quit to main menu r: restart current level z: undo a move (only works for past 256 moves and super buggy) Play: dice-is-you.dicec.tf

This challenge is a game inspired by the game Baba is you, which is a puzzle game where the player can change “the rules” by interacting with the blocks on the game. The Dice is you challenge was implemented using HTML + Javascript + WebAssembly (C language game logic + SDL).

DiceGang CTF 2021 - babyrop [pwn]

• Competition: DiceGang CTF 2021
• Challenge Name: BabyRop
• Type: Pwn
• Points: 116 pts
• Description:

  “FizzBuzz101: Who wants to write a ret2libc”

  nc dicec.tf 31924

This was a beginner level challenge which as the name suggests is all about ROP. Some basic fingerprinting on the babyrop binary gives us useful information, such as no canary and partial RelRO.

justCTF 2020 - That's not crypto [crypto]

• Competition: justCTF 2020
• Challenge Name: That’s not crypto
• Type: Crypto
• Points: 210 pts
• Description:

  This is very simple RE task, but you may need some other skills as well.

Downloaded checker.pyc. Decided to use https://pypi.org/project/uncompyle6 for decompilation.

The file consists of the following logic:

• A variable name a which is a list of big numbers. It’s interpreted as polynomial coefficients.
• Given a flag from the user, it calls function make_correct_array which derives an array from the given string.
• Calls validate(a, flag).

Crowdstrike CTF 2021 - Portal

• Competition: Crowdstrike CTF
• Challenge Name: Portal
• Points: 1 pts
• Description:

  PROTECTIVE PENGUIN gained access to one of their victims through the victim’s extranet authentication portals and we were asked to investigate. Please download the Portal Code and see whether you can reproduce their means of initial access vector. We stood up a test instance of the authentication portal for you to validate against.

The target for this challenge is located at https://authportal.challenges.adversary.zone:8880/cgi-bin/portal.cgi. By opening the Qemu image we can retrieve the ELF64 file: cgi-bin/portal.cgi. That “portal” is fairly basic, only asking for credentials.