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High, CVSS 8.8amended

Happy DOM ECMAScriptModuleCompiler: unsanitized export names are interpolated as executable code

CVE-2026-33943GHSA-6q6h-j7hj-3r64

What to do

Vendor fix available. Upgrade each affected package to the fixed version on its release line (happy-dom 20.8.8), redeploy, then verify what is actually installed.

This page has no inventory attached, so it cannot say whether you are affected. A vendor fix is not proof that your deployment is fixed.

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Affected packages

  • npm happy-dom

    Affected
    >= 15.10.0, <= 20.8.7
    Fixed in
    20.8.8

Sources

Severity and exploitation
Exploitation
No confirmed exploitation recorded. Patch Next marks exploitation only from CISA KEV.
CVSS
8.8 · CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:H/I:H/A:H
EPSS
  • CVE-2026-33943: 0.65% estimated exploitation activity in the next 30 days; percentile 51.03 (FIRST EPSS, 2026-11-03). This is a model estimate, not proof of exploitation or customer exposure.
Source description

As published by the source; long descriptions are shortened.

Summary 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. Details Vulnerable file: packages/happy-dom/src/module/ECMAScriptModuleCompiler.ts, lines 371-385 The "Export object" handler extracts content from export { ... } using the regex export\s{([^}]+)}, then generates executable code by directly interpolating it: } else if (match[16] && isTopLevel && PRECEDINGSTATEMENTTOKENREGEXP.test(precedingToken)) { // Export object const parts = this.removeMultilineComments(match[16]).split(/\s,\s/); const exportCode: string[] = []; for (const part of parts) { const nameParts =…

Dates and revisions
Published by the source
Last modified by the source
Source last checked
  1. Revision 2 · amended ·

    Amended from ghsa record GHSA-6q6h-j7hj-3r64

  2. Revision 1 · created ·

    Published from osv record GHSA-6q6h-j7hj-3r64

Agent brief

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# Patch Next advisory brief: CVE-2026-33943

Advisory: Happy DOM ECMAScriptModuleCompiler: unsanitized export names are interpolated as executable code
IDs: CVE-2026-33943, GHSA-6q6h-j7hj-3r64
Record: https://patchnext.com/advisories/cve-2026-33943 (revision 2, source checked 26 Oct 2026, 12:47 UTC)
Inventory: none attached. This brief comes from a public page and does not say whether any deployment is affected.
Severity: High (CVSS 8.8)
Exploitation: no confirmed exploitation recorded. Patch Next confirms exploitation only from CISA KEV.
Vendor response: Vendor fix available; fixed versions by package: happy-dom 20.8.8. A vendor fix does not mean a deployment is fixed.

## Affected components
- npm happy-dom: affected >= 15.10.0, <= 20.8.7; fixed in 20.8.8

## Suggested inspection (read-only)
- `npm ls happy-dom --all`: lists every installed copy and version, including transitive ones. Run in the project root after `npm ci`.

## Supported action
Upgrade each affected component to a fixed version on its release line. For a transitive dependency, upgrade the parent package or add an override or constraint, then regenerate the lockfile. Redeploy every environment that ran an affected version.

## Required regression checks
- Run the test suite and a production build.
- Exercise the features that depend on happy-dom.
- Repeat the inspection and confirm that only fixed versions remain installed.

## Rollback considerations
- Keep the previous lockfile and deployment artifact. Rolling back reinstates the vulnerable version, so apply any documented mitigation while you fix forward.

## Unresolved questions
- Which deployments run an affected version?
- Exploitation status can change. Check again before lowering the priority.
- Mark the work resolved only after the fixed version is verified in production.

## Sources
- Verified: https://osv.dev/vulnerability/GHSA-6q6h-j7hj-3r64 (OSV record GHSA-6q6h-j7hj-3r64 lists affected ranges: npm happy-dom >=15.10.0 <20.8.8 (fixed))
- Verified: https://github.com/advisories/GHSA-6q6h-j7hj-3r64 (GitHub-reviewed advisory GHSA-6q6h-j7hj-3r64 lists affected ranges: npm happy-dom >=15.10.0 <=20.8.7)

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