CVE-2026-78207
CriticalCVSS 9.4Summary
The exceljs-hardened library before version 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.
Risk Assessment
An attacker can manipulate application behavior, potentially leading to unauthorized access, privilege escalation, or other attacks depending on the context of library usage.
Recommendation
Update exceljs-hardened to version 5.0.0 or later, which includes a fix for this vulnerability.
Original NVD description (English source)
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.