{"affected":[{"defaultStatus":"unaffected","ecosystem":"npm","packageName":"exceljs","product":"exceljs","source":"CNA: VulnCheck","vendor":"exceljs","versions":[{"lessThanOrEqual":"4.4.0","status":"affected","version":"0","versionType":"semver"}]}],"cveId":"CVE-2026-128336","cwes":["CWE-1321"],"description":"ExcelJS through 4.4.0 contains a prototype pollution vulnerability that allows attackers to add numeric keys to Object.prototype through a crafted defined name referencing a __proto__ sheet. Attackers can supply an xlsx whose xl/workbook.xml definedName range targets __proto__, causing CellMatrix to write empty arrays onto Object.prototype process-wide when workbook.xlsx.load() runs.","epss":null,"exploits":[],"kev":null,"metrics":[{"score":6.3,"severity":"medium","source":"CNA: VulnCheck","vector":"CVSS:4.0/AV:N/AC:H/AT:P/PR:N/UI:N/VC:N/VI:L/VA:L/SC:N/SI:N/SA:N","version":"4.0"},{"score":4.8,"severity":"medium","source":"CNA: VulnCheck","vector":"CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:N/I:L/A:L","version":"3.1"},{"score":6.3,"severity":"medium","source":"NVD: disclosure@vulncheck.com","vector":"CVSS:4.0/AV:N/AC:H/AT:P/PR:N/UI:N/VC:N/VI:L/VA:L/SC:N/SI:N/SA:N/E:X/CR:X/IR:X/AR:X/MAV:X/MAC:X/MAT:X/MPR:X/MUI:X/MVC:X/MVI:X/MVA:X/MSC:X/MSI:X/MSA:X/S:X/AU:X/R:X/V:X/RE:X/U:X","version":"4.0"},{"score":4.8,"severity":"medium","source":"NVD: disclosure@vulncheck.com","vector":"CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:N/I:L/A:L","version":"3.1"}],"modifiedAt":1794565093757,"publishedAt":1794562418327,"references":[{"source":"CNA: VulnCheck","tags":["product"],"url":"https://github.com/exceljs/exceljs"},{"source":"CNA: VulnCheck","tags":["third-party-advisory"],"url":"https://github.com/mateocallec/exceljs-hardened/security/advisories/GHSA-pwgq-2cgg-6ph9"},{"source":"CNA: VulnCheck","tags":["technical-description"],"url":"https://github.com/exceljs/exceljs/blob/v4.4.0/lib/utils/cell-matrix.js#L50-L52"},{"source":"CNA: VulnCheck","tags":["technical-description"],"url":"https://github.com/exceljs/exceljs/blob/v4.4.0/lib/doc/defined-names.js#L182-L193"},{"source":"CNA: VulnCheck","tags":["third-party-advisory"],"url":"https://www.vulncheck.com/advisories/exceljs-through-4.4.0-prototype-pollution-via-proto-defined-name"},{"source":"disclosure@vulncheck.com","tags":[],"url":"https://github.com/exceljs/exceljs"},{"source":"disclosure@vulncheck.com","tags":[],"url":"https://github.com/exceljs/exceljs/blob/v4.4.0/lib/doc/defined-names.js#L182-L193"},{"source":"disclosure@vulncheck.com","tags":[],"url":"https://github.com/exceljs/exceljs/blob/v4.4.0/lib/utils/cell-matrix.js#L50-L52"},{"source":"disclosure@vulncheck.com","tags":[],"url":"https://github.com/mateocallec/exceljs-hardened/security/advisories/GHSA-pwgq-2cgg-6ph9"},{"source":"disclosure@vulncheck.com","tags":[],"url":"https://www.vulncheck.com/advisories/exceljs-through-4.4.0-prototype-pollution-via-proto-defined-name"}],"remediation":[],"revision":"efc7c2c9a27eebf8d5777164a4311b4d9b629c023f078b7acc5bf287ce21d06a","sources":[{"modifiedAt":1794562418327,"name":"CNA: VulnCheck","retrievedAt":1794564866329,"url":"https://www.cve.org/CVERecord?id=CVE-2026-128336"},{"modifiedAt":1794565093757,"name":"NVD","retrievedAt":1794572258239,"url":"https://nvd.nist.gov/vuln/detail/CVE-2026-128336"}],"ssvc":null,"status":"published","title":"ExcelJS through 4.4.0 Prototype Pollution via __proto__ Defined Name","updatedAt":1794572258239}