CVE-2026-78207
exceljs vulnerability
- Published23 Aug 2026
Description
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 3.1 breakdown
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:LRemediation
No fixed version is recorded in the NVD data. Check the vendor advisory for the latest guidance.
References
- https://github.com/exceljs/exceljs
- https://github.com/exceljs/exceljs/blob/v4.4.0/lib/utils/under-dash.js#L155-L181
- https://github.com/mateocallec/exceljs-hardened/security/advisories/GHSA-qwr4-7h29-chpf
- https://www.vulncheck.com/advisories/exceljs-through-prototype-pollution-via-deepmerge-reached-from-note-serialization
Related CVEs
Recent high-severity vulnerabilities sharing a weakness type.
Frequently asked
Is CVE-2026-78207 being actively exploited?
CVE-2026-78207 is not in the CISA KEV catalog. Its EPSS exploit probability is 0.60%.
How severe is CVE-2026-78207?
CVE-2026-78207 has a CVSS 3.1 base score of 9.4, rated critical. EPSS estimates a 0.60% probability of exploitation.
How do I fix CVE-2026-78207?
Apply the vendor's patch or advisory guidance, then verify no affected versions remain across your devices.
How Secuno handles this
Secuno correlates vulnerabilities like CVE-2026-78207 against the real software inventory on every managed device, as each hourly inventory arrives. Rather than a static severity, each match is scored in context: exploit availability, EPSS, the asset's exposure, and business criticality decide where it lands in the queue. If an affected version is present anywhere across your portfolio, it surfaces automatically with a prioritised remediation path.
Data from the NVD, CISA KEV catalog and FIRST EPSS. CVSS 3.1 base score shown where available.