Happy DOM GHSA-c8p4-j97h-3vg8 / CVE-2026-118660: parsing untrusted HTML makes the server fetch iframe and stylesheet URLs (SSRF). What changed in happy-dom 21.0.0 and how do I upgrade?

Applies to: npm happy-dom <= 20.14.6 parsing untrusted HTML (server-side rendering, scrapers, test runners with network access)

How it was checked: Compiled on 2026-10-28 from the Happy DOM GitHub security advisory, the GitHub Advisory Database entry and the 21.0.0 release notes; not reproduced by Exuvia.

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Fix

What it is: Happy DOM is a JavaScript implementation of a browser DOM, used in tests (Vitest, Bun) and sometimes on servers to parse or render HTML. Up to 20.14.6 it loaded iframe pages and <link rel="stylesheet"> files with real HTTP requests by default. If a server parses HTML from users (comments, emails, scraped pages, LLM output) with Happy DOM, that HTML can make the server request any URL, including internal services and cloud metadata addresses: server-side request forgery. Published October 28, 2026 (high); fixed in 21.0.0 by turning both kinds of loading off by default. Am I affected: - happy-dom 20.14.6 or earlier (npm ls happy-dom). - Real risk only when untrusted HTML is parsed in a process that can reach things worth protecting (production servers, CI runners with cloud credentials). Test suites that only load your own fixtures are low risk, but upgrading is still simple. Fix: 1. Upgrade to happy-dom 21.0.0 or later. It's a major version: iframe page loading and CSS file loading are now off by default, the old disableCSSFileLoading setting is deprecated, and the new settings are enableCSSFileLoading and enableIframePageLoading. 2. If your tests relied on loading CSS files or iframe pages, turn them back on only for trusted content: new Window({ settings: { enableCSSFileLoading: true, enableIframePageLoading: true } }). Don't enable them where untrusted HTML is parsed. 3. If you can't upgrade yet: set disableIframePageLoading: true and disableCSSFileLoading: true in the Window settings wherever untrusted HTML is parsed, and restrict the server's outbound network access (block internal ranges and 169.254.169.254). Verify: npm ls happy-dom shows 21.0.0+, and parsing a test page whose iframe/stylesheet points at a URL you control produces no request. Sources: https://github.com/capricorn86/happy-dom/security/advisories/GHSA-c8p4-j97h-3vg8 https://github.com/advisories/GHSA-c8p4-j97h-3vg8 https://github.com/capricorn86/happy-dom/releases/tag/v21.0.0

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