CVE
ExcelJS denial of service in data validation sqref handling
Affects ExcelJS 4.4.0 and earlier when an application loads attacker-supplied workbooks 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
- Not reported
Do first: Workaround: Until a fix is confirmed, stop passing untrusted workbooks to xlsx.load(). Limit that feature to files from trusted sources, or validate uploads before loading them.
- 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? →
- 31/100 · 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
Summary
ExcelJS through 4.4.0 contains a resource exhaustion vulnerability in data-validations-xform.js that allows attackers to exhaust CPU and memory by supplying unbounded sqref ranges. Attackers can provide a small crafted workbook with a sqref of A1:XFD1048576 to make xlsx.load() iterate billions of addresses, blocking the event loop and crashing the process with an uncatchable out-of-memory error.
Who should check
Teams running ExcelJS 4.4.0 or earlier that load untrusted .xlsx files with xlsx.load(), such as services accepting user uploads.
cve.now Index
- Exploitation?/40Unknown. No CISA SSVC exploitation rating yet
- Exposure17/25No login or user action needed, reachable over the network without a login · 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 76 if added to CISA KEV
- Would score about 71 if CISA's SSVC rates exploitation active
- Would score about 36 if advisories confirm default setups are exposed
What to do
Workaround: Until a fix is confirmed, stop passing untrusted workbooks to xlsx.load(). Limit that feature to files from trusted sources, or validate uploads before loading them.
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-2026-128341 (ExcelJS through 4.4.0 Denial of Service via Oversized Data Validation sqref), 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-2026-128341 (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 (exceljs <= 4.4.0). (source: https://www.vulncheck.com/advisories/exceljs-through-4.4.0-denial-of-service-via-oversized-data-validation-sqref)
- The application loads an attacker-supplied workbook with xlsx.load(). (source: https://www.vulncheck.com/advisories/exceljs-through-4.4.0-denial-of-service-via-oversized-data-validation-sqref)
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-2026-128341 is not listed as of cve.now's last read.
This KEV status is for CVE-2026-128341 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/issues/3093
- https://github.com/exceljs/exceljs
- https://github.com/mateocallec/exceljs-hardened/security/advisories/GHSA-f689-fh93-2pm2
- https://github.com/exceljs/exceljs/blob/v4.4.0/lib/xlsx/xform/sheet/data-validations-xform.js#L216-L227
- https://www.vulncheck.com/advisories/exceljs-through-4.4.0-denial-of-service-via-oversized-data-validation-sqref
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-2026-128341
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-2026-128341"}.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
- Report
- Repository
- Repository
- Link
Corrections
None so far.
Something wrong on this page? Report an error. Every fix is listed here.
Questions about CVE-2026-128341
Is CVE-2026-128341 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?
A small crafted workbook with a data validation sqref of A1:XFD1048576 makes xlsx.load() iterate billions of addresses. This exhausts CPU and memory, blocks the event loop, and crashes the process with an out-of-memory error that cannot be caught.Source: vulncheck.com
Which versions are affected by CVE-2026-128341?
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, but only where the application calls xlsx.load() on workbooks an attacker can supply. To check the setup, look at the exceljs version in the project's package.json or the output of npm ls exceljs, and search the code for xlsx.load() calls that read external files.Source: vulncheck.com
How do I fix CVE-2026-128341?
The checked facts do not name a fixed version or vendor patch, so no upgrade target can be confirmed from them. Check the ExcelJS release notes or advisory for a fix before choosing a version to move to.Source: vulncheck.com
What if there's no patch?
Until a fix is confirmed, stop passing untrusted workbooks to xlsx.load(). Limit that feature to files from trusted sources, or validate uploads before loading them.Source: vulncheck.com