Home/CVE/Happy DOM is a JavaScript implementation of a web browser without its graphical user interface. Versions prior to 20.8.9
CVE

CVE-2026-34226

Happy DOM is a JavaScript implementation of a web browser without its graphical user interface. Versions prior to 20.8.9

Happy DOM is a JavaScript implementation of a web browser without its graphical user interface. Versions prior to 20.8.9 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.

Version 20.8.9 fixes the issue.

HIGH · CVSS 7.5 EPSS 0.00054
Act now
  • Public exploit or PoC is available
  • SSVC automatable: yes - attacks can be scripted at scale
  • CVSS base score ≥ 7.0
Sigma rules0 YARA rules0
⬡

Weakness Classification

CWE-201Insertion of Sensitive Information Into Sent Data
CWE-359Exposure of Private Personal Information to an Unauthorized Actor
▤

Affected Products & Versions

1
capricorn86 happy dom< 20.8.9
▤

Affected Packages

1
Language-ecosystem packages (from OSV) tied to this CVE, with the version that fixes it - the dependency-level detail NVD doesn’t carry.
npm happy-dom HIGH fixed in 20.8.9
⚠

Public Exploits & PoCs

1
pocgithub.com · GHSA-w4gp-fjgq-3q4ggithub.com
▣

Scoring & Timeline

7.5
HIGH · CVSS v3.1 · security-advisories@github.com
View on NVD
Attack Vector
Network Adjacent Local Physical
Attack Complexity
Low High
Privileges Required
None Low High
User Interaction
None Required
Scope
Unchanged Changed
Confidentiality
None Low High
Integrity
None Low High
Availability
None Low High
Published to NVD27 Mar 2026 · 10:16 PM
CVSS VectorCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:N/A:N
SSVC triage · cisa-vulnrichment
Exploitation
poc
Automatable
yes
Technical impact
partial
SSVC asks the questions that actually drive patch urgency: is it being exploited, can attacks be automated, and how total is the impact.
🔗

References & Sources

4
Source URLs (vendor pages, mailing lists, write-ups). Exploit/PoC links are in their own section above to avoid duplication.
https://github.com/capricorn86/happy-dom/blob/f8d8cad41e9722fab9eefb9dfb3cca696462e908/packages/happy-dom/src/fetch/utilities/FetchRequestHeaderUtility.tsPatch
https://github.com/capricorn86/happy-dom/commit/68324c21d7b98f53f7bb5a7b3e185bda7106e751Patch
https://github.com/capricorn86/happy-dom/pull/2117Issue TrackingPatch
https://github.com/capricorn86/happy-dom/releases/tag/v20.8.9ProductRelease Notes
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