ExcelJS through 4.4.0 contains a prototype pollution vulnerability in mergeConditionalFormattings that allows attackers to modify Object.prototype by supplying an x14:cfRule id of __proto__. Attackers can craft an xlsx file that, when loaded with xlsx.load(), sets properties such as type, direction, border and cfvo on every object in the process until it restarts.

Attack Vector Network

Attack Complexity High

Privileges Required None

Attack Requirements Present

User Interaction None

Vulnerable System Confidentiality Impact Low

Vulnerable System Integrity Impact High

Vulnerable System Availability Impact Low

Subsequent System Confidentiality Impact None

Subsequent System Integrity Impact None

Subsequent System Availability Impact None

Attack Vector Network

Attack Complexity High

Privileges Required None

Scope Unchanged

Confidentiality Impact Low

Integrity Impact High

Availability Impact Low

User Interaction None

No CVSS v3.0

No CVSS v2

This CVE is not in the KEV list.

No EPSS score available.

Key SSVC decision points have not yet been added.

Default status is the baseline for the product, each version can override it (e.g. patched versions marked unaffected).

Vendor Product Default status Versions
exceljs exceljs unaffected
Version Status Constraints
0 affected ≤ 4.4.0

No data.

No data.

No data.

Project Subscriptions

Vendors Products
Exceljs Project Subscribe
Exceljs Subscribe
Advisories

No advisories yet.

Fixes

Solution

No solution given by the vendor.

Workaround

No workaround given by the vendor.

References
Link Providers
https://github.com/exceljs/exceljs cve-icon
https://github.com/exceljs/exceljs/blob/v4.4.0/lib/xlsx/xform/sheet/worksheet-xform.js#L34-L42 cve-icon
https://github.com/exceljs/exceljs/blob/v4.4.0/lib/xlsx/xform/sheet/worksheet-xform.js#L55-L74 cve-icon
https://github.com/mateocallec/exceljs-hardened/security/advisories/GHSA-86ch-m4gp-r5xf cve-icon
https://www.vulncheck.com/advisories/exceljs-through-4.4.0-prototype-pollution-via-x14-conditional-formatting-rule-id cve-icon
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 in mergeConditionalFormattings that allows attackers to modify Object.prototype by supplying an x14:cfRule id of __proto__. Attackers can craft an xlsx file that, when loaded with xlsx.load(), sets properties such as type, direction, border and cfvo on every object in the process until it restarts.
Title ExcelJS through 4.4.0 Prototype Pollution via x14 Conditional Formatting Rule ID
First Time appeared Exceljs Project
Exceljs Project exceljs
Weaknesses CWE-1321
CPEs cpe:2.3:a:exceljs_project:exceljs:*:*:*:*:*:*:*:*
Vendors & Products Exceljs Project
Exceljs Project exceljs
References
Metrics cvssV3_1

{'score': 7, 'vector': 'CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:L/I:H/A:L'}

cvssV4_0

{'score': 8.3, 'vector': 'CVSS:4.0/AV:N/AC:H/AT:P/PR:N/UI:N/VC:L/VI:H/VA:L/SC:N/SI:N/SA:N'}

Projects

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cve-icon MITRE

Status: PUBLISHED

Assigner: VulnCheck

Published:

Updated: 2026-11-13T09:33:37.679Z

Reserved: 2026-11-13T01:20:39.850Z

Link: CVE-2026-128337

cve-icon Vulnrichment

No data.

cve-icon NVD

No data.

cve-icon Redhat

No data.

cve-icon OpenCVE Enrichment

No data.

Weaknesses