CRITICAL 9.3 NVD
CVE-2026-78207
exceljs-hardened before 5.0.0 contains a prototype pollution vulnerability in the deepMerge helper that fails to reject __proto__, constructor, or prototype key
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.
References
- https://github.com/exceljs/exceljs
- https://github.com/exceljs/exceljs/blob/v4.4.0/lib/utils/under-dash.js#L155-L181
- https://github.com/mateocallec/exceljs-hardened/security/advisories/GHSA-qwr4-7h29-chpf
- https://www.vulncheck.com/advisories/exceljs-through-prototype-pollution-via-deepmerge-rea
This critical severity vulnerability with a CVSS score of 9.3 was published on 2026-08-24 via NVD.
Risk Timeline
CVE Disclosed2026-08-24 · -1 days ago
Remediation Resources
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