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CVE-2026-128337

7, high

exceljs Prototype Pollution Vulnerability

NVD (opens in a new tab) CVE.org (opens in a new tab)
CVSS
7, high high CVSS v3.1
EPSS, next 30 days
0.4% higher than 39.1% of scored CVEs
Exploitation
No public evidence
Published
13 Nov 2026yesterday

Description

ExcelJS through 4.4.0 contains a prototype pollution vulnerability in mergeConditionalFormattings that allows attackers to modify Object.prototype by supplying an x14:cfRule id of __proto__. Attackers can craft an xlsx file that, when loaded with xlsx.load(), sets properties such as type, direction, border and cfvo on every object in the process until it restarts.

Details

Vendor
Exceljs
Product
exceljs
Weakness
CWE-1321 (opens in a new tab)
Status
Awaiting analysis
Updated
13 Nov 2026
Assigner
disclosure@vulncheck.com

CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:L/I:H/A:L

References 5

Advisories 1

Other references 4

The kind is read from NVD's tags where present and from the shape of the URL otherwise, so treat it as a hint.

Other Exceljs CVEs

Every Exceljs CVE we hold

Same vendor in what we hold, not a known link between the flaws.

  • CVE-2026-128338 exceljs Allocation of Resources Without Limits or Throttling Vulnerability EPSS 0.6% 7.5, high
  • CVE-2026-128341 exceljs Allocation of Resources Without Limits or Throttling Vulnerability EPSS 0.6% 7.5, high
  • CVE-2026-128342 ExcelJS through 4.4.0 contains a denial of service vulnerability that allows attackers to block the event loop by supplying an unbounded… EPSS 0.6% 7.5, high
  • CVE-2026-128346 ExcelJS through 4.4.0 contains a resource leak vulnerability in the streaming WorkbookReader.parse that leaves temporary files and open… EPSS 0.6% 7.5, high

Beyond this page

Is CVE-2026-128337 in your network?

This page tells you how dangerous CVE-2026-128337 is out there. Whether it sits on one of your devices, only a scan of your own network can tell. That is what our systems do, every day, for the companies we protect.

  • EXYS7600 OCELOT

    Find it before attackers do

    Ocelot scans your network on a schedule and reports every vulnerability it finds by its CVE identifier, with its CVSS score and how many of your hosts are affected. A finding like CVE-2026-128337 comes with the devices to patch.

    Learn more about EXYS7600 OCELOT

  • EXYS7950 KONDRA

    Detect it if it's exploited

    Until the patch is applied, Kondra monitors your network, events and endpoints in real time. It keeps an inventory of the software installed on every endpoint, and its anomaly detection rules flag what an attacker does once inside.

    Learn more about EXYS7950 KONDRA
Check your exposure

Assembled from the NVD 2.0 API, the CISA Known Exploited Vulnerabilities Catalog and FIRST EPSS. Scores are as of our last collection on 14 Nov 2026, not the live upstream state.