CVE-2026-128336
ExcelJS through 4.4.0 Prototype Pollution via __proto__ Defined Name
CVSS Score
4.8
EPSS Score
0.0%
EPSS Percentile
0th
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.
| CWE | CWE-1321 |
| Vendor | exceljs |
| Product | exceljs |
| Published | Nov 13, 2026 |
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CVSS v3 Breakdown
CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:N/I:L/A:L Attack Vector
Network
Attack Complexity
High
Privileges Required
None
User Interaction
None
Scope
Unchanged
Confidentiality
None
Integrity
Low
Availability
Low
Affected Versions
exceljs / exceljs
0 ≤ 4.4.0
References
github.com: https://github.com/exceljs/exceljs github.com: https://github.com/mateocallec/exceljs-hardened/security/advisories/GHSA-pwgq-2cgg-6ph9 github.com: https://github.com/exceljs/exceljs/blob/v4.4.0/lib/utils/cell-matrix.js#L50-L52 github.com: https://github.com/exceljs/exceljs/blob/v4.4.0/lib/doc/defined-names.js#L182-L193 vulncheck.com: https://www.vulncheck.com/advisories/exceljs-through-4.4.0-prototype-pollution-via-proto-defined-name
Credits
Matéo Florian Callec