CVE-2026-78207
exceljs through 4.4.0 Prototype Pollution via deepMerge Reached From Note Serialization
CVSS Score
9.4
EPSS Score
0.0%
EPSS Percentile
0th
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.
| CWE | CWE-1321 |
| Vendor | exceljs |
| Product | exceljs |
| Published | Aug 24, 2026 |
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CVSS v3 Breakdown
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:L Attack Vector
Network
Attack Complexity
Low
Privileges Required
None
User Interaction
None
Scope
Unchanged
Confidentiality
High
Integrity
High
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-qwr4-7h29-chpf github.com: https://github.com/exceljs/exceljs/blob/v4.4.0/lib/utils/under-dash.js#L155-L181 vulncheck.com: https://www.vulncheck.com/advisories/exceljs-through-prototype-pollution-via-deepmerge-reached-from-note-serialization
Credits
Matéo Florian Callec