TI-2026-54393 Aliases CVE-2026-78207 GHSA-3cpv-r8x3-29fp

exceljs through 4.4.0 Prototype Pollution via deepMerge Reached From Note Serialization

MEDIUM 49CWE-1321Published 2026-08-24 · Updated 2026-11-08

Key facts

Attack vector: Network
Privileges required: None
User interaction: None
Attack complexity: Low
Attack requirements: None
Impact type: —
Confidentiality · integrity · availability: High · High · Low
Fix status: No fix listed

Attack profile from CVSS 4.0 · CNA. Fix status from CNA.

Summary

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.

Why it matters now

Exploitation None reported CISA SSVC · not in CISA KEV

EPSS 0.00603 49th percentileScored 2026-11-07

Fix No fix listed No fixed version in the sources yet

SSVC decision points

CISA ADP · SSVC 2.0.3

Exploitation: None
Automatable: Yes
Technical impact: Total

The decision (Track, Attend, Act) also depends on your mission and well-being impact; see CISA's SSVC guide.

Affected products

Vendor	Product	Affected versions	Fixed in	Status	Source
exceljs	exceljs	up to 4.4.0	—	No fix listed	CNA

exceljs Vendorexceljs Affected up to 4.4.0 Fixed in — No fix listed CNA

Remediation

No fixed version listed by the sources yet.

Timeline

2026-10-02 Threatist record created from CVE-2026-78207
2026-10-03 Alias added: GHSA-3cpv-r8x3-29fp

References

Advisory 1

GitHub Security Advisory (GHSA-qwr4-7h29-chpf)

Other 2

TI-2026-54392 exceljs through 4.4.0 Uncontrolled Resource Consumption via Unbounded xlsx Decompression CVSS 4.0HIGH 8.7
TI-2026-54394 exceljs through 4.4.0 Path Traversal via Unvalidated addImage filename CVSS 4.0HIGH 8.7
TI-2026-54395 exceljs through 4.4.0 CSV Formula Injection via Unescaped Cell Values CVSS 4.0HIGH 8.4

Sources

This product uses the NVD API but is not endorsed or certified by the NVD. Sources and licences