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

Q: How do I fix CVE-2026-33943?

happy dom: upgrade to 20.8.8. Exact commands for each OS are on this page.

Q: Is CVE-2026-33943 being exploited?

CVE-2026-33943 is not on the CISA Known Exploited Vulnerabilities list at the time of the last update. Check again, as this can change.

Q: What does CVE-2026-33943 affect?

CVE-2026-33943 affects happy dom. Severity is high (CVSS 8.8). Happy DOM is a JavaScript implementation of a web browser without its graphical user interface. In versions 15.10.0 through 20.8.7, a code injection vulnerability in `ECMAScriptModuleCompiler` allows an attacker to achieve Remote Code Execu

Q: How urgent is CVE-2026-33943?

Priority 48/100. High severity; Public exploit reference

This month

HIGH 8.8UPGRADE

CVE-2026-33943 is a high-severity flaw (CVSS 8.8) 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. In versions 15.10.0 through 20.8.7, a code injection vulnerability in `ECMAScriptModuleCompiler` allows an attacker to achieve Remote Code Execution (RCE) by injecting arbitrary JavaScript expressions inside `export { }` declarations in ES module scripts processed by happy-dom. The compiler directly interpolates unsanitized content into generated code

Why this priority

High severity
Public exploit reference

A fixed release or distro patch exists.

Risk facts

CVSS score	8.8 (High)
Attack vector	Network (remote)
Attack complexity	Low
Privileges needed	None
User interaction	Required
EPSS exploit chance	0.6% (top 49%)
CISA exploited list	No
Weakness	CWE-94, CWE-917
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 00:10 UTCUpdated Record last modified

capricorn86 happy dom UPGRADE

Affected: >= 15.10.0 and < 20.8.8

Fixed in: 20.8.8

Safe to downgrade to: a release before 15.10.0

1. Check installed version

npm ls happy-dom

2. UPGRADE to 20.8.8

npm install happy-dom@">=20.8.8"

3. If no update is available yet, DOWNGRADE to a release before 15.10.0

npm view happy-dom versions npm install happy-dom@"<15.10.0"

Downgrade risk

Downgrading can break dependent software and may reopen older bugs. Read the distro advisory first and test on a non-production host.

After downgrade

Restart the service, and keep the package held until a fixed release ships.

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-2026-33943?

happy dom: upgrade to 20.8.8. Exact commands for each OS are on this page.

Is CVE-2026-33943 being exploited?

CVE-2026-33943 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-2026-33943 affect?

CVE-2026-33943 affects happy dom. Severity is high (CVSS 8.8). Happy DOM is a JavaScript implementation of a web browser without its graphical user interface. In versions 15.10.0 through 20.8.7, a code injection vulnerability in `ECMAScriptModuleCompiler` allows an attacker to achieve Remote Code Execu

How urgent is CVE-2026-33943?

Priority 48/100. High severity; Public exploit reference

References

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