CVE-2026-78207
exceljs through 4.4.0 Prototype Pollution via deepMerge Reached From Note Serialization
- State
- Published
- Severity
- 9.3 Critical
- Published
- Aug 24, 2026
- Updated
- Aug 29, 2026
- Reserved
- Aug 24, 2026
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.
Scores
| CVSS | Score | Vector | Source |
|---|---|---|---|
| 4.0 | 9.3 Critical | 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 | VulnCheck |
| 3.1 | 9.4 Critical | CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:L | VulnCheck |
Weaknesses
- CWE-1321 Improperly Controlled Modification of Object Prototype Attributes ('Prototype Pollution')
Affected Products
| Product | Versions |
|---|---|
exceljsexceljs |
|
References
- https://github.com/exceljs/exceljsproduct
- GitHub Security Advisory (GHSA-qwr4-7h29-chpf)third-party-advisory
- https://github.com/exceljs/exceljs/blob/v4.4.0/lib/utils/under-dash.js#L155-L181technical-description
- VulnCheck Advisory: exceljs through 4.4.0 Prototype Pollution via deepMerge Reached From Note Serializationthird-party-advisory
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