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.
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References
History
Fri, 13 Nov 2026 09:45:00 +0000
| Type | Values Removed | Values Added |
|---|---|---|
| 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. | |
| Title | ExcelJS through 4.4.0 Prototype Pollution via __proto__ Defined Name | |
| First Time appeared |
Exceljs Project
Exceljs Project exceljs |
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| Weaknesses | CWE-1321 | |
| CPEs | cpe:2.3:a:exceljs_project:exceljs:*:*:*:*:*:*:*:* | |
| Vendors & Products |
Exceljs Project
Exceljs Project exceljs |
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| Metrics |
cvssV3_1
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MITRE
Status: PUBLISHED
Assigner: VulnCheck
Published:
Updated: 2026-11-13T09:33:38.327Z
Reserved: 2026-11-13T01:20:38.540Z
Link: CVE-2026-128336
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Weaknesses