---
id: "CVE-2026-128342"
page: "https://infrastack.ai/live/CVE-2026-128342"
kind: "vulnerability"
aliases: ["CVE-2026-128342"]
title: "ExcelJS: crafted workbook sheetId stalls the Node event loop"
severity: "high"
cvss: 8.7
epss: null
exploited: false
status: "open"
category: "package"
products: []
ecosystems: []
tags: ["exceljs", "node", "npm", "package"]
not_affected_if: ["no-untrusted-xlsx-input"]
published_at: "2026-11-13T10:18:14+00:00"
first_seen_at: "2026-11-13T10:47:34+00:00"
updated_at: "2026-11-13T10:49:16+00:00"
sources: [{"source": "nvd", "url": "https://nvd.nist.gov/vuln/detail/CVE-2026-128342", "first_seen_at": "2026-11-13T10:47:34+00:00"}]
exploit_sources: []
---

# ExcelJS: crafted workbook sheetId stalls the Node event loop

Link for people: https://infrastack.ai/live/CVE-2026-128342 (this .md is for agents)

ExcelJS through 4.4.0 trusts the sheetId value in xl/workbook.xml without a bound. A crafted spreadsheet with a huge sheetId makes worksheet lookups stall the event loop for seconds.

_Summary, check and fix written by a model from the sources; labelled as such._

## How to check

- Check the installed version with `npm ls exceljs`
- Find where the app parses uploaded or untrusted .xlsx files with ExcelJS, such as `Workbook.xlsx.load` or `readFile`

## Fix

- Move to a release newer than `4.4.0`; the sources do not name the fixed version

## Timeline

- 2026-11-13T10:47:34+00:00 nvd https://nvd.nist.gov/vuln/detail/CVE-2026-128342

## Documents

- [advisory] Vendor advisory: github.com https://github.com/mateocallec/exceljs-hardened/security/advisories/GHSA-9vv6-5g3h-prg5
- [advisory] Third-party advisory: www.vulncheck.com https://www.vulncheck.com/advisories/exceljs-through-4.4.0-denial-of-service-via-oversized-worksheet-sheetid

## From the sources

ExcelJS through 4.4.0 contains a denial of service vulnerability that allows attackers to block the event loop by supplying an unbounded sheetId in xl/workbook.xml. Attackers can provide a workbook with a huge sheetId, making the sparse worksheet array walk stall worksheets, getWorksheet and writeBuffer for seconds.

---

_Free to read, with fair use of about 60 pages a minute. For higher limits or API access: sales@infrastack.ai_