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CVE-2026-78207 Details

UNDERGOING ENRICHMENT

The CVE is currently being enriched by the Volerion team. The enrichment process results in the association of reference link tags, CVSS, and CPE applicability statement data.

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.

Metrics

CVSS 3.x Severity and Vector Strings:

VolerionCVSS-B:…Vector:This vulnerability is currently being analyzed.

CNA: [email protected]CVSS-B:9.4 CRITICALVector:CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:L

References to Advisories, Solutions, and Tools

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URL	Source(s)	Tag(s)
https://github.com/exceljs/exceljs	[email protected]
https://github.com/exceljs/exceljs/blob/v4.4.0/lib/utils/under-dash.js#L155-L181	[email protected]
https://github.com/mateocallec/exceljs-hardened/security/advisories/GHSA-qwr4-7h29-chpf	[email protected]
https://www.vulncheck.com/advisories/exceljs-through-prototype-pollution-via-deepmerge-reached-from-note-serialization	[email protected]

Weakness Enumeration

CWE-ID	CWE Name	Source
CWE-1321	Improperly Controlled Modification of Object Prototype Attributes ('Prototype Pollution')	[email protected]

Affected Products

This vulnerability is currently being analyzed

Change History

3 change records found show changes

Date	Action	Recorded By
Aug 29, 2026	CVE Modified	[email protected]
Aug 24, 2026	CVE Modified	CISA-ADP
Aug 24, 2026	New CVE Received	[email protected]