How severe is CVE-2026-33943?

CVE-2026-33943 has a CVSS 3.x base score of 8.8, rated high severity. It is exploitable over network with low attack complexity, requires no privileges and user interaction. Impact on confidentiality is high, integrity high, and availability high.

Is CVE-2026-33943 being actively exploited?

It is not currently listed in CISA's KEV catalog. Its EPSS exploit-prediction score is 1% (52nd percentile), an estimate of the probability of exploitation in the next 30 days.

What products are affected by CVE-2026-33943?

CVE-2026-33943 affects Capricorn86 Happy Dom. See the affected-products list for the exact vulnerable versions.

How do I fix CVE-2026-33943?

Review the linked vendor and NVD advisories for patched versions and mitigations, then upgrade or apply the recommended workaround. Given its high severity, prioritise patching exposed systems.

Does CVE-2026-33943 have an EU (EUVD) identifier?

Yes. CVE-2026-33943 is tracked in the ENISA EU Vulnerability Database (EUVD) as EUVD-2026-16864.

When was CVE-2026-33943 published?

CVE-2026-33943 was published on 2026-03-27 and last updated on 2026-06-30.

CVE-2026-33943

CVE-2026-33943 is a high-severity vulnerability in Capricorn86 Happy Dom with a CVSS 3.x base score of 8.8. It is not currently listed as actively exploited by CISA, and its EPSS exploit-prediction score is low. The underlying weakness is classified as CWE-94.

Key facts

Severity: High (CVSS 3.x base score 8.8)
EPSS exploit prediction: 1% (52nd percentile)
Actively exploited: Not listed in CISA KEV
EU (EUVD) id: EUVD-2026-16864
Weakness: CWE-94
Affected product: Capricorn86 Happy Dom
Published: 2026-03-27
Last modified: 2026-06-30

Description

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 as an executable expression, and the quote filter does not strip backticks, allowing template literal-based payloads to bypass sanitization. Version 20.8.8 fixes the issue.

Frequently asked questions

What is CVE-2026-33943?: 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 as an executable expression, and the quote filter does not strip backticks, allowing template literal-based payloads to bypass sanitization. Version 20.8.8 fixes the issue.
How severe is CVE-2026-33943?: CVE-2026-33943 has a CVSS 3.x base score of 8.8, rated high severity. It is exploitable over network with low attack complexity, requires no privileges and user interaction. Impact on confidentiality is high, integrity high, and availability high.
Is CVE-2026-33943 being actively exploited?: It is not currently listed in CISA's KEV catalog. Its EPSS exploit-prediction score is 1% (52nd percentile), an estimate of the probability of exploitation in the next 30 days.
What products are affected by CVE-2026-33943?: CVE-2026-33943 affects Capricorn86 Happy Dom. See the affected-products list for the exact vulnerable versions.
How do I fix CVE-2026-33943?: Review the linked vendor and NVD advisories for patched versions and mitigations, then upgrade or apply the recommended workaround. Given its high severity, prioritise patching exposed systems.
Does CVE-2026-33943 have an EU (EUVD) identifier?: Yes. CVE-2026-33943 is tracked in the ENISA EU Vulnerability Database (EUVD) as EUVD-2026-16864.
When was CVE-2026-33943 published?: CVE-2026-33943 was published on 2026-03-27 and last updated on 2026-06-30.

References

Affected products (1)

cpe:2.3:a:capricorn86:happy_dom:*:*:*:*:*:node.js:*:*

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