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...