CVE-2026-128336
Published:November 13, 2026
Updated:November 13, 2026
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.
Affected Packages
https://github.com/mateocallec/exceljs-hardened.git (GITHUB):
Affected version(s) >=v5.0.0 <v5.1.0Fix Suggestion:
Update to version v5.1.0exceljs-hardened (NPM):
Affected version(s) >=5.0.0 <5.1.0Fix Suggestion:
Update to version 5.1.0Additional Notes
The description of this vulnerability differs from MITRE.
Related Resources (6)
Do you need more information?
Contact UsCVSS v4
Base Score:
6.3
Attack Vector
NETWORK
Attack Complexity
HIGH
Attack Requirements
PRESENT
Privileges Required
NONE
User Interaction
NONE
Vulnerable System Confidentiality
NONE
Vulnerable System Integrity
LOW
Vulnerable System Availability
LOW
Subsequent System Confidentiality
NONE
Subsequent System Integrity
NONE
Subsequent System Availability
NONE
CVSS v3
Base Score:
4.8
Attack Vector
NETWORK
Attack Complexity
HIGH
Privileges Required
NONE
User Interaction
NONE
Scope
UNCHANGED
Confidentiality
NONE
Integrity
LOW
Availability
LOW
Weakness Type (CWE)
Improperly Controlled Modification of Object Prototype Attributes