CVE
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.
Written by anthropic/claude-haiku-5.5 from the sources below. Verify against them.
- Exploited
- Proof of concept public, per CISA
- Fix
- See vendor advisory
- Who is exposed
- Not reported
Do first: Workaround: 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.
- Published
- Last modified
- Whether it needs action now or is a reference record, by fixed rules, with why. Last checked is when cve.now last re-read it.What do these mean? →
- Reference
- Last checked
- FIRST's estimate of the chance attackers exploit it in the next 30 days, updated daily.What do these mean? →
- 0.63% · 50th percentile
- A 0-100 score for how much a CVE matters across the industry: exploitation, exposure, how widely the software is used, severity and whether a fix exists.What do these mean? →
- 49/100 · provisional
- How many real-world setups can hit the bug, from the vendor's advisory and CISA data. It does not know your setup.What do these mean? →
- Unclear
- Whether working attack code is public (Exploit-DB, Metasploit, Nuclei or GitHub). Public code makes attacks easier.What do these mean? →
- None on Exploit-DB, Metasploit or GitHub
- Exploitation: poc
- Automatable: yes
- Technical impact: partial
Summary
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$1048576 from xl/workbook.xml cell by cell, causing an uncatchable fatal heap out-of-memory error during xlsx.load().
Who should check
Teams running ExcelJS 4.4.0 or earlier that call xlsx.load() on untrusted .xlsx files
cve.now Index
- Exploitation15/40CISA rates a proof of concept as public
- Exposure20/25No login or user action needed, CISA rates it automatable · Unknown: Advisories don't say whether default setups are affected
- Reach?/20Unknown. No tracked technology or package matched
- Severity8.7/10CVSS 8.7
- No patch5/5No fixed version listed; see vendor advisory
What would change the score
- Would score about 79 if added to CISA KEV
- Would score about 74 if CISA's SSVC rates exploitation active
- Would score about 54 if advisories confirm default setups are exposed
What to do
Workaround: No patch is listed in the checked facts. Limit exposure by not loading workbooks from untrusted sources with xlsx.load(), since the crash happens during loading.
Check your systems with an agent
Paste this into a coding or ops agent. It checks your systems read-only and reports a table per asset.
Check whether my systems are affected by CVE-2026-128340 (ExcelJS through 4.4.0 Memory Exhaustion via Oversized Defined Name Range), using the cve.now data below.
Rules: work read-only. Do not run exploit code, proof-of-concept scripts or scanners that send attack payloads, and do not change any configuration, package, image or deployment. Report findings only.
What cve.now has for CVE-2026-128340 (entry last updated 2026-11-13):
Affected:
- exceljs exceljs: through 4.4.0
Fixed versions: none listed yet.
Conditions (all must be true for the bug to be hit):
- ExcelJS version 4.4.0 or earlier (source: https://www.vulncheck.com/advisories/exceljs-through-4.4.0-memory-exhaustion-via-oversized-defined-name-range)
- The workbook's xl/workbook.xml contains an oversized defined-name cell range, such as S!$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"}.Timeline
- CVE published
- First seen by cve.now
- CISA SSVC assessment
Exploitation: poc · Automatable: yes · Technical impact: partial
- Record last updated
Affected versions
- exceljs exceljs
through 4.4.0
Evidence 7
Vendor advisory · 1
Establishes: Affected and fixed versions.
- Advisory
CVE record · 2
Establishes: The identifier and description.
- Record
- Record
Other links · 4
- Repository
- Repository
- Repository
- Link
Corrections
None so far.
Something wrong on this page? Report an error. Every fix is listed here.
Questions about CVE-2026-128340
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: cve.now feed data
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: vulncheck.com
Which versions are affected by CVE-2026-128340?
exceljs: through 4.4.0.Source: cve.now feed data
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: vulncheck.com
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: vulncheck.com
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: vulncheck.com