Capture The Flag At UCF - Scripting Repetition solution with Node.js

homework.js

const net = require('net');
const client = new net.Socket();
const math = require('mathjs'); // requires mathjs package!

client.connect(10104, 'ctf.hackucf.org');

client.on('data', data => {
  const text = data.toString();
  const flag = /flag{.*}/gm.exec(text);

  if (flag) {
    console.log();
    console.log(`We got the flag! The flag is ${flag[0]}`);
    return client.destroy();
  }

  if (text.includes(' = ')) {
    const innerMost = eval(text.split('((')[1].split(')')[0]);
    const inner = eval(innerMost + text.split(')')[1]);
    const outer = eval(inner + text.split(')')[2].split(' =')[0]);

    client.write(`${outer}\r\n`);
  }

  process.stdout.write('.');
});

const eval = equation => Math.floor(math.eval(equation));

repetition-1.js

const net = require('net');
const client = new net.Socket();

client.connect(10101, 'ctf.hackucf.org');

client.on('data', data => {
  const text = data.toString();
  const flag = /flag{.*}/gm.exec(text);

  if (flag) {
    console.log();
    console.log(`We got the flag! The flag is ${flag[0]}`);
    return client.destroy();
  }

  if (text.includes('Value')) {
    process.stdout.write('.');
    const number = parseInt(text.split('Value')[1].replace(/^\D+/g, ''));
    client.write(`${number}\r\n`);
  }
});

repetition-2.js

const net = require('net');
const client = new net.Socket();

client.connect(10102, 'ctf.hackucf.org');

let firstValue;

client.on('data', data => {
  const text = data.toString();
  const flag = /flag{.*}/gm.exec(text);

  if (flag) {
    console.log();
    console.log(`We got the flag! The flag is ${flag[0]}`);
    return client.destroy();
  }

  if (text.includes('first value')) {
    client.write(`${firstValue}\r\n`);
  } else if (text.includes('Value')) {
    const number = parseInt(text.split('Value')[1].replace(/^\D+/g, ''));
    client.write(`${number}\r\n`);

    if (firstValue === undefined) {
      firstValue = number;
    }
  }

  process.stdout.write('.');
});