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Vulnerability record · CVE-2026-33943 · published 27 March 2026

CVE-2026-33943: Capricorn86 happy dom code injection vulnerability

CCapricorn86 · Happy Dom

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.

9.8 CVSS 3.1 Critical EPSS 0.97% · top 39.6% CWE-94 · Code injectionCWE-917 · Expression language injection
9.8CVSS 3.1 base score
0.97%EPSS exploitation probability, 30 days
NoNot in CISA KEV
1Affected product versions listed by NVD
7References, 2 tagged exploit
15 Jul 2026Last modified by NVD

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.

CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H

Affected products

1 vulnerable configurations from NVD's CPE data, grouped by vendor and product.

References

LinkTags
https://github.com/capricorn86/happy-dom/commit/5437fdf8f13adb9590f9f52616d9f69c3ee8db3c Patch
https://github.com/capricorn86/happy-dom/releases/tag/v20.8.8 ProductRelease Notes
https://github.com/capricorn86/happy-dom/security/advisories/GHSA-6q6h-j7hj-3r64 ExploitVendor Advisory
https://access.redhat.com/security/cve/CVE-2026-33943
https://bugzilla.redhat.com/show_bug.cgi?id=2452522
https://github.com/capricorn86/happy-dom/security/advisories/GHSA-6q6h-j7hj-3r64 ExploitVendor Advisory
https://security.access.redhat.com/data/csaf/v2/vex/2026/cve-2026-33943.json

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Source: NIST National Vulnerability Database (record CVE-2026-33943), CISA KEV, FIRST EPSS (scores of 2026-09-27). This page is refreshed as NVD updates the record.