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CVE-2026-128336

MediumCVSS 4.8/10Last modified Nov 13, 2026

Description

ExcelJS through 4.4.0 contains a prototype pollution vulnerability that allows attackers to add numeric keys to Object.prototype through a crafted defined name referencing a __proto__ sheet. Attackers can supply an xlsx whose xl/workbook.xml definedName range targets __proto__, causing CellMatrix to write empty arrays onto Object.prototype process-wide when workbook.xlsx.load() runs.

Metrics

CVSS 3.1 4.8/10CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:N/I:L/A:L

Weakness enumeration

Affected software

No affected versions have been published.

Timeline

Published: Nov 13, 2026
Last modified: Nov 13, 2026
NVD status: Deferred

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CVE-2026-128336: Medium severity, CVSS 4.8 | Vulnix