CVE-2026-78207: critical vulnerability in exceljs
exceljs through 4.4.0 Prototype Pollution via deepMerge Reached From Note Serialization
Published · Updated
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28Vexday Risk Score
No sign of exploitation. No public exploitation artifact known so far.
ssvc Trackcvss 9.3epss 0.6%
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:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:H/VI:H/VA:L/SC:N/SI:N/SA:N
Affected products
exceljs · exceljsRelated CVEs — exceljs
In the same product, most dangerous first.
CVE-2026-78206HIGHexceljs through 4.4.0 Uncontrolled Resource Consumption via Unbounded xlsx DecompressionEPSS 0.6%CVE-2026-78208HIGHexceljs through 4.4.0 Path Traversal via Unvalidated addImage filenameEPSS 0.5%CVE-2026-78209HIGHexceljs through 4.4.0 CSV Formula Injection via Unescaped Cell ValuesEPSS 0.4%
References
https://github.com/exceljs/exceljshttps://github.com/exceljs/exceljs/blob/v4.4.0/lib/utils/under-dash.js#L155-L181https://github.com/mateocallec/exceljs-hardened/security/advisories/GHSA-qwr4-7h29-chpfhttps://www.vulncheck.com/advisories/exceljs-through-prototype-pollution-via-deepmerge-reached-from-note-serialization