Description
exceljs through 4.4.0 contains a prototype pollution vulnerability in the deepMerge helper that fails to reject __proto__, constructor, or prototype keys when merging note objects. Attackers can assign parsed JSON with a malicious __proto__ property to cell notes, modifying Object.prototype and affecting all plain objects created in the process.
Published: 2026-08-24
Score: 9.3 Critical
EPSS: < 1% Very Low
KEV: No
Impact: n/a
Action: n/a
AI Analysis

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Remediation

No vendor fix or workaround currently provided.

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Tracking

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Advisories

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History

Sat, 29 Aug 2026 12:00:00 +0000

Type Values Removed Values Added
Description exceljs-hardened before 5.0.0 contains a prototype pollution vulnerability in the deepMerge helper that fails to reject __proto__, constructor, or prototype keys when merging note objects. Attackers can assign parsed JSON with a malicious __proto__ property to cell notes, modifying Object.prototype and affecting all plain objects created in the process. exceljs through 4.4.0 contains a prototype pollution vulnerability in the deepMerge helper that fails to reject __proto__, constructor, or prototype keys when merging note objects. Attackers can assign parsed JSON with a malicious __proto__ property to cell notes, modifying Object.prototype and affecting all plain objects created in the process.

Mon, 24 Aug 2026 18:30:00 +0000

Type Values Removed Values Added
Metrics ssvc

{'options': {'Automatable': 'yes', 'Exploitation': 'none', 'Technical Impact': 'total'}, 'version': '2.0.3'}


Mon, 24 Aug 2026 00:45:00 +0000

Type Values Removed Values Added
Description exceljs-hardened before 5.0.0 contains a prototype pollution vulnerability in the deepMerge helper that fails to reject __proto__, constructor, or prototype keys when merging note objects. Attackers can assign parsed JSON with a malicious __proto__ property to cell notes, modifying Object.prototype and affecting all plain objects created in the process.
Title exceljs through 4.4.0 Prototype Pollution via deepMerge Reached From Note Serialization
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': 9.4, 'vector': 'CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:L'}

cvssV4_0

{'score': 9.3, 'vector': 'CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:H/VI:H/VA:L/SC:N/SI:N/SA:N'}


Subscriptions

Exceljs Project Exceljs
cve-icon MITRE

Status: PUBLISHED

Assigner: VulnCheck

Published:

Updated: 2026-08-29T11:47:57.933Z

Reserved: 2026-08-24T00:15:01.656Z

Link: CVE-2026-78207

cve-icon Vulnrichment

Updated: 2026-08-24T17:46:54.055Z

cve-icon NVD

Status : Received

Published: 2026-08-24T01:16:58.137

Modified: 2026-08-29T12:16:48.753

Link: CVE-2026-78207

cve-icon Redhat

No data.

cve-icon OpenCVE Enrichment

Updated: 2026-08-29T14:30:05Z

Weaknesses