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CVE-2026-78207

9.3 critical SSVC exploitation: none Deferred
NVD · CVE.org

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.

Fix

Nothing published yet: no patch, vendor advisory or mitigation reference on NVD, no vendor advisory in the News for this CVE, not in CISA's KEV, no fixed package version. BaselineWatch does not guess at one.

Change history 1

  1. First seenCVSS 9.3NVD modified 2026-10-14 13:10

Affected (CPE criteria) 0

NVD has not attached CPE configurations yet.

References 4