CVE-2026-34226: Happy DOM is a JavaScript implementation of a web browser without its graphical user interface

This week

HIGH 7.5REMOTEUPGRADE

CVE-2026-34226 is a high-severity flaw (CVSS 7.5) affecting happy dom. Below: why it ranks where it does, which versions are affected, what to do, and the exact commands.

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.

Why this priority

High severity
Public exploit reference
Remotely exploitable, no login, no user action

A fixed release or distro patch exists.

Risk facts

CVSS score	7.5 (High)
Attack vector	Network (remote)
Attack complexity	Low
Privileges needed	None
User interaction	None
EPSS exploit chance	0.5% (top 60%)
CISA exploited list	No
Weakness	CWE-201, CWE-359
Published	2026-03-27
Last modified	2026-10-26

Publisher (CNA): GitHub, Inc. · Vendor: capricorn86

Last updated 2026-10-26 · Sources: CVE Program, NVD, CISA KEV, EPSS and vendor advisories · How we score

Am I affected?

Timeline

2026-03-27 22:16 UTCPublished CVE record published
2026-10-26 21:10 UTCUpdated Record last modified

capricorn86 happy dom UPGRADE

Affected: < 20.8.9

Fixed in: 20.8.9

Safe to downgrade to: no unaffected older release

1. Check installed version

npm ls happy-dom

2. UPGRADE to 20.8.9

npm install happy-dom@">=20.8.9"

Verify at the official source NVD · CVE Program · Report a problem with this page
Scores and fixes here are computed automatically from those and other public sources. Confirm with the vendor advisory before changing production systems.

Quick answers

How do I fix CVE-2026-34226?

happy dom: upgrade to 20.8.9. Exact commands for each OS are on this page.

Is CVE-2026-34226 being exploited?

CVE-2026-34226 is not on the CISA Known Exploited Vulnerabilities list at the time of the last update. Check again, as this can change.

What does CVE-2026-34226 affect?

CVE-2026-34226 affects happy dom. Severity is high (CVSS 7.5). 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(...,

How urgent is CVE-2026-34226?

Priority 46/100. High severity; Public exploit reference; Remotely exploitable, no login, no user action

Related CVEs

CVE-2026-33943 HIGH 8.8 UPGRADE Happy DOM is a JavaScript implementation of a web browser without its graphical user interface

References

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