8.8 High

Happy DOM: Incomplete fix for CVE-2026-33943: unsanitized import alias leads to host code execution

CVE-2026-115895

Summary The ESM compiler in happy-dom@20.14.5 does not validate imported local binding aliases before interpolating them into generated JavaScript. As a result, an invalid ESM import alias can be transformed into a valid JavaScript destructuring default initializer and executed. This appears to be an alternate injection path and incomplete remediation of GHSA-6q6h-j7hj-3r64 / CVE-2026-33943. The previous fix validates importName in the local export { ... } handler, but the named import handler still places an unvalidated alias directly into code context. These issues were confirmed through the public Window and APIs using the published happy-dom npm package. The PoC reaches the Node.js host process, obtains node:fs, and creates a proof directory on the host filesystem. Confirmed affected versions The PoC was directly tested against: happy-dom@17.0.0 happy-dom@20.0.0 happy-dom@20.1.0 happy-dom@20.14.5 The same PoC does not trigger on happy-dom@16.8.1. The ESM compiler was introduced by commit 7bc831df2, first released in v17.0.0. The vulnerable interpolation remains present through v20.14.5, the latest release at the time of testing. Suggested affected range: text = 17.0.0,…

Assessment

CVSS: 8.8 (v3.1)
Severity: High
EPSS: 0.00473% chance of exploitation in the next 30 days
Known exploited: Not listed in CISA KEV
Exploit availability: Nothing found in Exploit-DB, Metasploit, Nuclei or public PoC repositories
Published: 23 October 2026
Last updated: 23 October 2026
Affected: npm · happy-dom
Weakness: CWE-94

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

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