Happy DOM: SSRF via iframe and link stylesheet when parsing untrusted HTML

Exploitation

No confirmed exploitation recorded. Patch Next marks exploitation only from CISA KEV.

CVSS

8.6 · CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:C/C:H/I:N/A:N

EPSS

• CVE-2026-118660: 0.40% estimated exploitation activity in the next 30 days; percentile 34.78 (FIRST EPSS, 2026-11-03). This is a model estimate, not proof of exploitation or customer exposure.

As published by the source; long descriptions are shortened.

Summary happy-dom v20.8.9 makes real server-side HTTP requests to arbitrary URLs when parsing HTML containing ` ` or ` ` elements. This behavior is enabled by default (`disableIframePageLoading: false`, `disableCSSFileLoading: false`). When an application uses happy-dom to parse untrusted HTML on the server side, an attacker can trigger Server-Side Request Forgery by embedding these elements.

Affected Versions - happy-dom ` stylesheets fetch their `href` URL via real HTTP requests When untrusted HTML is parsed, these elements trigger real server-side HTTP requests to whatever URLs are specified. No special configuration or opt-in is needed.

Proof of Concept

Verified test (attacker server receives requests): ```javascript const http = require('http'); const { Window } = require('happy-dom'); // Start attacker server const srv = http.createServer((req, res) => { console.log(`SSRF HIT: ${req.method} ${req.url}`); res.writeHead(200, {'Content-Type': 'text/html'}); res.end('…

Published by the source

28 Oct 2026, 21:06 UTC

Last modified by the source

28 Oct 2026, 21:15 UTC

Source last checked

29 Oct 2026, 06:00 UTC

1. Revision 2 · amended · 29 Oct 2026

   Amended from osv record GHSA-c8p4-j97h-3vg8

2. Revision 1 · created · 28 Oct 2026

   Published from ghsa record GHSA-c8p4-j97h-3vg8

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# Patch Next advisory brief: CVE-2026-118660

Advisory: Happy DOM: SSRF via iframe and link stylesheet when parsing untrusted HTML
IDs: CVE-2026-118660, GHSA-c8p4-j97h-3vg8
Record: https://patchnext.com/advisories/cve-2026-118660 (revision 2, source checked 29 Oct 2026, 06:00 UTC)
Inventory: none attached. This brief comes from a public page and does not say whether any deployment is affected.
Severity: High (CVSS 8.6)
Exploitation: no confirmed exploitation recorded. Patch Next confirms exploitation only from CISA KEV.
Vendor response: Vendor fix available; fixed versions by package: happy-dom 21.0.0. A vendor fix does not mean a deployment is fixed.

## Affected components
- npm happy-dom: affected < 21.0.0; fixed in 21.0.0

## Suggested inspection (read-only)
- `npm ls happy-dom --all`: lists every installed copy and version, including transitive ones. Run in the project root after `npm ci`.

## Supported action
Upgrade each affected component to a fixed version on its release line. For a transitive dependency, upgrade the parent package or add an override or constraint, then regenerate the lockfile. Redeploy every environment that ran an affected version.

## Required regression checks
- Run the test suite and a production build.
- Exercise the features that depend on happy-dom.
- Repeat the inspection and confirm that only fixed versions remain installed.

## Rollback considerations
- Keep the previous lockfile and deployment artifact. Rolling back reinstates the vulnerable version, so apply any documented mitigation while you fix forward.

## Unresolved questions
- Which deployments run an affected version?
- Exploitation status can change. Check again before lowering the priority.
- Mark the work resolved only after the fixed version is verified in production.

## Sources
- Verified: https://github.com/advisories/GHSA-c8p4-j97h-3vg8 (GitHub-reviewed advisory GHSA-c8p4-j97h-3vg8 lists affected ranges: npm happy-dom >=0 <=20.14.6)
- Verified: https://osv.dev/vulnerability/GHSA-c8p4-j97h-3vg8 (OSV record GHSA-c8p4-j97h-3vg8 lists affected ranges: npm happy-dom >=0 <21.0.0 (fixed))

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