CVE
ExcelJS memory exhaustion in worksheet column parsing
Affects exceljs 4.4.0 and earlier when a workbook with a worksheet col element that has an unbounded max attribute is loaded with xlsx.load(). No fixed version is listed in the checked facts.
Written by anthropic/claude-haiku-5.5 from the sources below. Verify against them.
- Exploited
- No known exploitation
- Fix
- See vendor advisory
- Who is exposed
- Default setups
Do first: Check every install: default setups are affected.
- 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? →
- 36/100 · 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? →
- Default setups
- 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
Summary
exceljs through 4.4.0 contains a memory exhaustion vulnerability that allows attackers to crash applications by supplying a worksheet col element with an unbounded max attribute. Attackers can craft a small workbook with a huge max value, causing xlsx.load() to allocate hundreds of millions of Column objects and abort the process with an uncatchable heap out-of-memory error.
Who should check
Teams loading untrusted .xlsx files with exceljs 4.4.0 or earlier via xlsx.load(), such as services accepting user uploads.
cve.now Index
- Exploitation?/40Unknown. No CISA SSVC exploitation rating yet
- Exposure22/25Default setups, reachable over the network without a login
- 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 76 if added to CISA KEV
- Would score about 71 if CISA's SSVC rates exploitation active
What to do
Check every install: default setups are affected.
Workaround: The checked facts give no workaround. Limiting exposure means not loading workbooks from untrusted sources with xlsx.load() until a fix is available.
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-2026-128338 (ExcelJS through 4.4.0 Memory Exhaustion via Unbounded Worksheet Column 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-2026-128338 (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-unbounded-worksheet-column-range)
- The workbook contains a worksheet col element with an unbounded max attribute, loaded with xlsx.load() (source: https://www.vulncheck.com/advisories/exceljs-through-4.4.0-memory-exhaustion-via-unbounded-worksheet-column-range)
Setup: the bug is reachable in a default setup; no special feature or setting is needed.
Attacker needs: network access, no login, no user action.
CISA KEV: CVE-2026-128338 is not listed as of cve.now's last read.
This KEV status is for CVE-2026-128338 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-w57r-3mm6-w6g7
- https://github.com/exceljs/exceljs/blob/v4.4.0/lib/doc/column.js#L307-L316
- https://github.com/exceljs/exceljs/blob/v4.4.0/lib/xlsx/xform/sheet/col-xform.js#L43-L47
- https://www.vulncheck.com/advisories/exceljs-through-4.4.0-memory-exhaustion-via-unbounded-worksheet-column-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-2026-128338
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-2026-128338"}.Timeline
- CVE published
- First seen by cve.now
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-2026-128338
Is CVE-2026-128338 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: cve.now feed data
What does this mean?
Loading a workbook with a worksheet col element that has an unbounded max attribute can exhaust memory. The Node.js process then crashes with an out-of-memory abort that try/catch cannot handle.Source: vulncheck.com, github.com
Which versions are affected by CVE-2026-128338?
exceljs: through 4.4.0.Source: cve.now feed data
Am I affected, and how do I check?
exceljs version 4.4.0 or earlier is affected, and the trigger is a workbook containing a worksheet col element with an unbounded max attribute that is loaded with xlsx.load(). To check the installed version, look at the exceljs entry in the project's lockfile or run npm ls exceljs.Source: vulncheck.com, github.com
How do I fix CVE-2026-128338?
The checked facts name no fixed version or vendor patch, so no upgrade target can be given. Check the advisory for a fix before relying on any version.Source: vulncheck.com, github.com
What if there's no patch?
The checked facts give no workaround. Limiting exposure means not loading workbooks from untrusted sources with xlsx.load() until a fix is available.Source: vulncheck.com, github.com