CVE-2026-78207
exceljs through 4.4.0 Prototype Pollution via deepMerge Reached From Note Serialization
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.
Fixes and workarounds
No remediation reported in collected sources.
Missing remediation information is not evidence that no patch exists.
Affected products and versions
| Product | Versions | Authority |
|---|---|---|
| exceljs exceljs exceljs
npm |
≥ 0; ≤ 4.4.0 (affected, semver)
Other versions: unaffected |
CNA: VulnCheck |
Version ranges are source assertions. Check the vendor advisory and your installed configuration before determining exposure.
CVSS assessments
| Version / score | Vector | Authority |
|---|---|---|
| 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 | CNA: 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 | CNA: VulnCheck |
Exploit evidence
No exploit evidence in collected sources. This is not proof of no exploitation.
References
- https://github.com/exceljs/exceljsCNA: VulnCheck · product
- https://github.com/mateocallec/exceljs-hardened/security/advisories/GHSA-qwr4-7h29-chpfCNA: VulnCheck · third-party-advisory, vendor-advisory
- https://github.com/exceljs/exceljs/blob/v4.4.0/lib/utils/under-dash.js#L155-L181CNA: VulnCheck · technical-description
- https://www.vulncheck.com/advisories/exceljs-through-prototype-pollution-via-deepmerge-reached-from-note-serializationCNA: VulnCheck · third-party-advisory
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