Vulnerability 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.
CVSS Score
CRITICAL
Related Weaknesses (CWE)
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-qwr4-7h
- https://www.vulncheck.com/advisories/exceljs-through-prototype-pollution-via-dee
FAQ
What is CVE-2026-78207?
CVE-2026-78207 is a vulnerability with a CVSS score of 9.4 (CRITICAL). 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 assig...
How severe is CVE-2026-78207?
CVE-2026-78207 has been rated CRITICAL with a CVSS base score of 9.4/10. This is considered a critical vulnerability requiring immediate attention.
Is there a patch for CVE-2026-78207?
Check the references section above for vendor advisories and patch information. Review vendor security bulletins for remediation guidance.