by Kastro
Paper/Archive/CVE-2026-78207

CVE-2026-78207

exceljs exceljs — exceljs through 4.4.0 Prototype Pollution via deepMerge Reached From Note Serialization

EPSS 0.6%CVSS 9.4
critical.is priorityof 100
38
CVSS 9.4 (CNA)9.4 / 10 × 3028.2Not in CISA KEV+300.0EPSS percentile 48.9.489 × 209.8No public exploit+100.0SSVC exploitation: none+100.0
Description · from the CVE record

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.

Affected

ProductAffectedFixed inSource
exceljs≤ 4.4.0–CNA

Scores by source

VulnCheck (CNA)9.4CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:L
VulnCheck (CNA)9.3CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:H/VI:H/VA:L/SC:N/SI:N/SA:N
CISA ADPSSVCExploitation: none · Automatable: yes · Technical impact: total

References

refgithub.com/exceljs/exceljswriteupgithub.com/mateocallec/exceljs-hardened/security/advisories/GHSA-qwr4-7h29-chpfwriteupgithub.com/exceljs/exceljs/blob/v4.4.0/lib/utils/under-dash.js#L155-L181writeupvulncheck.com/advisories/exceljs-through-prototype-pollution-via-deepmerge-reached-from-note-serialization