Mutation XSS Challenge (patched)

index2.js

const { JSDOM } = require('jsdom');
const http = require("http");

function parseConsistent(html) {
    let prevHtml = '';

    for (let i = 0; i < 10; i++) {
        // Parse until HTML is the same twice
        dom = new JSDOM(html);
        html = dom.window.document.body.innerHTML;
        if (html === prevHtml) {
            return dom;
        }
        prevHtml = html;
    }

    throw new Error('HTML is inconsistent');
}

function sanitize(html) {
    if (html.length > 1000) {
        throw new Error('HTML is too long');
    }

    const { document, NodeFilter } = parseConsistent(html).window;

    // Remove comments
    const nodeIterator = document.createNodeIterator(document.body, NodeFilter.SHOW_COMMENT);
    while (nodeIterator.nextNode()) {
        nodeIterator.referenceNode.remove();
    }
    // Remove dangerous text nodes
    const dangerousTags = document.querySelectorAll(
        'script, iframe, style, xmp, noembed, noframes, noscript, plaintext, template');
    dangerousTags.forEach(tag => tag.remove());

    // Remove all attributes
    const allTags = document.querySelectorAll('*');
    allTags.forEach(tag => {
        const attributes = Array.from(tag.attributes);
        attributes.forEach(attr => tag.removeAttribute(attr.name));
    });

    return document.body.innerHTML;
}

const server = http.createServer((req, res) => {
    const params = new URLSearchParams(req.url.split('?')[1]);
    const html = params.get('html') || '';
    res.setHeader('Content-Type', 'text/html; charset=utf-8');
    res.end(sanitize(html));
});

const PORT = process.env.PORT || 3000;
server.listen(PORT, () => {
    console.log(`Server is running http://localhost:${PORT}`);
});