{"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-2026-128337","cwes":["CWE-1321"],"description":"ExcelJS through 4.4.0 contains a prototype pollution vulnerability in mergeConditionalFormattings that allows attackers to modify Object.prototype by supplying an x14:cfRule id of __proto__. Attackers can craft an xlsx file that, when loaded with xlsx.load(), sets properties such as type, direction, border and cfvo on every object in the process until it restarts.","epss":null,"exploits":[],"kev":null,"metrics":[{"score":8.3,"severity":"high","source":"CNA: VulnCheck","vector":"CVSS:4.0/AV:N/AC:H/AT:P/PR:N/UI:N/VC:L/VI:H/VA:L/SC:N/SI:N/SA:N","version":"4.0"},{"score":7,"severity":"high","source":"CNA: VulnCheck","vector":"CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:L/I:H/A:L","version":"3.1"},{"score":8.3,"severity":"high","source":"NVD: disclosure@vulncheck.com","vector":"CVSS:4.0/AV:N/AC:H/AT:P/PR:N/UI:N/VC:L/VI:H/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":7,"severity":"high","source":"NVD: disclosure@vulncheck.com","vector":"CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:L/I:H/A:L","version":"3.1"}],"modifiedAt":1794565093920,"publishedAt":1794562417679,"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-86ch-m4gp-r5xf"},{"source":"CNA: VulnCheck","tags":["technical-description"],"url":"https://github.com/exceljs/exceljs/blob/v4.4.0/lib/xlsx/xform/sheet/worksheet-xform.js#L34-L42"},{"source":"CNA: VulnCheck","tags":["technical-description"],"url":"https://github.com/exceljs/exceljs/blob/v4.4.0/lib/xlsx/xform/sheet/worksheet-xform.js#L55-L74"},{"source":"CNA: VulnCheck","tags":["third-party-advisory"],"url":"https://www.vulncheck.com/advisories/exceljs-through-4.4.0-prototype-pollution-via-x14-conditional-formatting-rule-id"},{"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/xlsx/xform/sheet/worksheet-xform.js#L34-L42"},{"source":"disclosure@vulncheck.com","tags":[],"url":"https://github.com/exceljs/exceljs/blob/v4.4.0/lib/xlsx/xform/sheet/worksheet-xform.js#L55-L74"},{"source":"disclosure@vulncheck.com","tags":[],"url":"https://github.com/mateocallec/exceljs-hardened/security/advisories/GHSA-86ch-m4gp-r5xf"},{"source":"disclosure@vulncheck.com","tags":[],"url":"https://www.vulncheck.com/advisories/exceljs-through-4.4.0-prototype-pollution-via-x14-conditional-formatting-rule-id"}],"remediation":[],"revision":"453ef4861e2f17322be8ce7bb17eff967e88892ad4ead4eaddefb6930d3fce07","sources":[{"modifiedAt":1794562417679,"name":"CNA: VulnCheck","retrievedAt":1794564867439,"url":"https://www.cve.org/CVERecord?id=CVE-2026-128337"},{"modifiedAt":1794565093920,"name":"NVD","retrievedAt":1794572258396,"url":"https://nvd.nist.gov/vuln/detail/CVE-2026-128337"}],"ssvc":null,"status":"published","title":"ExcelJS through 4.4.0 Prototype Pollution via x14 Conditional Formatting Rule ID","updatedAt":1794572258396}