Vulnerability record/PUBLISHED/Published Aug 24, 2026 00:30:47 UTC
CVE-2026-78207
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.
Base score9.3/ 10
SeverityCriticalCVSS 4.0
Exploitability / impact
CVSS metric breakdown
Base severityCritical
Attack vectorNetworkAV
Attack complexityLowAC
Attack requirementsNoneAT
Privileges requiredNonePR
User interactionNoneUI
Vulnerable system confidentialityHighVC
Vulnerable system integrityHighVI
Vulnerable system availabilityLowVA
Subsequent system confidentialityNoneSC
Subsequent system integrityNoneSI
Subsequent system availabilityNoneSA
CVSS vector string
CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:H/VI:H/VA:L/SC:N/SI:N/SA:NCVSS communicates standardized severity and impact characteristics. It does not establish whether a system is exploitable in your specific environment.
Record context
CVE Numbering AuthorityVulnCheck
Last updatedNov 8, 2026 14:09:03 UTC
PublishedAug 24, 2026 00:30:47 UTC
ReservedAug 24, 2026 00:15:01 UTC
Credits
- Matéo Florian Callec