Beg-o-Matic 3000

Description

Ever wish someone would just GIVE you the flag if you asked nicely?

Source: beg-o-matic.zip

Author: @tsuto

Solution

As the name suggest we have to beg for flags 🤣

Beg-o-Matic_3000.png

From given source quick glance at middleware.js gives us attack vector idea: XSS

import { NextResponse } from 'next/server'
 
export function middleware(request) {
  const nonce = Buffer.from(crypto.randomUUID()).toString('base64')
  const cspHeader = `
    default-src 'self';
    script-src 'self' 'nonce-${nonce}';
    style-src 'self' 'unsafe-inline' *;
    img-src 'self' 'unsafe-inline' *;
    font-src 'self';
    object-src 'none';
    base-uri 'self';
    form-action 'self';
    frame-ancestors 'none';
    upgrade-insecure-requests;
`
  // Replace newline characters and spaces
  const contentSecurityPolicyHeaderValue = cspHeader.replace(/\s{2,}/g, ' ').trim()
 
  const requestHeaders = new Headers(request.headers)
  requestHeaders.set('x-nonce', nonce)
  requestHeaders.set('Content-Security-Policy', contentSecurityPolicyHeaderValue)
 
  const response = NextResponse.next({ request: { headers: requestHeaders, }, })
  response.headers.set('Content-Security-Policy', contentSecurityPolicyHeaderValue)
 
  return response
}

utils/bot.js is used to emulate the admin

import puppeteer from 'puppeteer';
import {setTimeout} from "node:timers/promises";
import dotenv from 'dotenv';
dotenv.config();

const botSecret = process.env.BOT_SECRET;

export async function launchBot(id) {
  const browser = await puppeteer.launch({ headless: true, args: ['--no-sandbox'], });
  const page = await browser.newPage();
  await page.setExtraHTTPHeaders({ 'X-Bot-Auth': botSecret, });
  console.log(`[BOT] Visiting submission ID: ${id}`)
  await page.goto(`http://localhost:3000/admin/${id}`, { waitUntil: 'networkidle2', });
  await setTimeout(3000);
  await browser.close();
  console.log(`[BOT] Done!`)
}

/api/list endpoint returns the flag only if the post is approved by the bot, so if we manage to approve the post can leak the flag.

Beg-o-Matic_3000-1.png

app/admin/[id]/page.js:

import { getSubmissionById } from "../../../db/actions";
import { approveBegging } from "@/app/actions";
import { headers } from "next/headers";

import dotenv from "dotenv";
dotenv.config();

const botSecret = process.env.BOT_SECRET;

console.log(`[BOT] Bot secret is: ${botSecret}`);

export default async function AdminPage({ params }) {
    const { id } = await params;
    const page_headers = await headers();
    const authHeader = await page_headers.get("x-bot-auth");
    const isDev = process.env.NODE_ENV === "development";

    if (!isDev && authHeader !== botSecret) {
        return <div>404 Not Found</div>; // or redirect to home
    }

    const submission = getSubmissionById(id);
    if (!submission) return <div>Submission not found</div>;

    return (
        <div className="p-8">
            <h1 className="text-xl font-bold">Admin Review</h1>
            <form action={approveBegging}>
                <input type="hidden" name="id" value={submission.id} />
                <button type="submit" className="mt-4 bg-green-600 text-white px-4 py-2 rounded"> Approve </button>
            </form>
            <div dangerouslySetInnerHTML={{ __html: submission.msg }} />
        </div>
    );
}

When bot views our submission React uses dangerouslySetInnerHTML to render our message, exposing bot to XSS attack as long as we can bypass the CSP.

This might not be so easy as it sounds...

default-src 'self'; script-src 'self' 'nonce-ZTg0ODI1MDYtYTc2Mi00OTRmLWIzZTgtODRlZTg0YzI5YTY2'; style-src 'self' 'unsafe-inline' *; img-src 'self' 'unsafe-inline' *; font-src 'self'; object-src 'none'; base-uri 'self'; form-action 'self'; frame-ancestors 'none'; upgrade-insecure-requests;

Beg-o-Matic_3000-2.png

Similar challenges (research~):

1. https://blog.arkark.dev/2023/12/28/seccon-finals/

2. https://blog.huli.tw/2022/08/21/en/corctf-2022-modern-blog-writeup/

3. https://waituck.sg/2023/12/11/0ctf-2023-newdiary-writeup.html

4. https://brycec.me/posts/corctf_2022_challenges

The solution was easier then expected, I was just overthinking about leaking the tokens with CSS, but you just needed header that bot head 💀. Dont overthink.

Solution by other players: USCG Beg-o-matic 3000 (CSRF) by FlagHoarders

@clovismint solution:

Beg-o-Matic_3000-3.png