{"id":"CVE-2026-128337","aliases":[],"cve":{"records":[{"id":"CVE-2026-128337","source":"VulnCheck","state":"PUBLISHED","reasons":[],"replacements":[],"disputed":false,"unsupportedWhenAssigned":false,"reserved":"2026-11-13T01:20:39.850Z","published":"2026-11-13T09:33:37.679Z","modified":"2026-11-13T09:33:37.679Z"}],"publishers":[{"name":"VulnCheck","role":"CNA","organizationId":"83251b91-4cc7-4094-a5c7-464a1b83ea10","modified":"2026-11-13T09:33:37.679Z"}],"references":[{"url":"https://github.com/exceljs/exceljs","tags":["product"],"source":"VulnCheck"},{"url":"https://github.com/mateocallec/exceljs-hardened/security/advisories/GHSA-86ch-m4gp-r5xf","tags":["third-party-advisory"],"source":"VulnCheck"},{"url":"https://github.com/exceljs/exceljs/blob/v4.4.0/lib/xlsx/xform/sheet/worksheet-xform.js#L34-L42","tags":["technical-description"],"source":"VulnCheck"},{"url":"https://github.com/exceljs/exceljs/blob/v4.4.0/lib/xlsx/xform/sheet/worksheet-xform.js#L55-L74","tags":["technical-description"],"source":"VulnCheck"},{"url":"https://www.vulncheck.com/advisories/exceljs-through-4.4.0-prototype-pollution-via-x14-conditional-formatting-rule-id","tags":["third-party-advisory"],"source":"VulnCheck"}],"weaknesses":[{"id":"CWE-1321","description":"Improperly Controlled Modification of Object Prototype Attributes ('Prototype Pollution')","source":"VulnCheck"}],"applicability":[{"source":"VulnCheck","statements":[{"nodes":[{"operator":"OR","negate":false,"cpeMatch":[{"vulnerable":true,"criteria":"cpe:2.3:a:exceljs_project:exceljs:*:*:*:*:*:*:*:*","versionEndIncluding":"4.4.0"}]}]}]}],"prioritization":[]},"title":"ExcelJS through 4.4.0 Prototype Pollution via x14 Conditional Formatting Rule ID","titleSource":"VulnCheck","descriptionSource":"VulnCheck","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restarts.","score":8.3,"severity":"high","published":"2026-11-13T09:33:37.679Z","modified":"2026-11-13T09:33:37.679Z","withdrawn":false,"knownExploited":false,"affected":[],"products":[{"vendor":"exceljs","name":"exceljs","platforms":[],"versions":[{"version":"0","status":"affected","lessThanOrEqual":"4.4.0","versionType":"semver"}],"defaultStatus":"unaffected","packageURL":"pkg:npm/exceljs","packageIdentity":{"ecosystem":"npm","name":"exceljs"},"cpes":[],"source":"VulnCheck","url":"https://www.cve.org/CVERecord?id=CVE-2026-128337"}],"remediation":[],"references":["https://github.com/exceljs/exceljs","https://github.com/mateocallec/exceljs-hardened/security/advisories/GHSA-86ch-m4gp-r5xf","https://github.com/exceljs/exceljs/blob/v4.4.0/lib/xlsx/xform/sheet/worksheet-xform.js#L34-L42","https://github.com/exceljs/exceljs/blob/v4.4.0/lib/xlsx/xform/sheet/worksheet-xform.js#L55-L74","https://www.vulncheck.com/advisories/exceljs-through-4.4.0-prototype-pollution-via-x14-conditional-formatting-rule-id"],"sources":[{"name":"CVE","id":"CVE-2026-128337","modified":"2026-11-13T09:33:37.679Z","url":"https://www.cve.org/CVERecord?id=CVE-2026-128337"}],"assessments":[{"source":"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","score":8.3},{"source":"VulnCheck","vector":"CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:L/I:H/A:L","score":7}],"sourceAffected":[],"observedAt":"2026-11-13T17:58:05.129Z","kev":{"status":"not-listed","checkedAt":"2026-11-15T00:15:33.603Z"},"coverage":[{"source":"NVD","status":"refresh-failed","attemptedAt":"2026-11-14T09:10:33.338Z"},{"source":"GHSA","status":"available","checkedAt":"2026-11-14T09:00:31.401Z","attemptedAt":"2026-11-14T09:00:31.401Z"},{"source":"EUVD","status":"available","checkedAt":"2026-11-14T08:50:31.925Z","attemptedAt":"2026-11-14T08:50:31.925Z"},{"source":"EPSS","status":"available","checkedAt":"2026-11-14T08:50:32.355Z","attemptedAt":"2026-11-14T08:50:32.355Z"}],"evidence":[{"source":"ENISA EUVD","id":"EUVD-2026-125040","url":"https://euvd.enisa.europa.eu/vulnerability/EUVD-2026-125040","modified":"Nov 13, 2026, 9:33:37 AM","score":8.3,"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","checkedAt":"2026-11-14T08:50:31.925Z"},{"source":"FIRST EPSS","id":"CVE-2026-128337","url":"https://www.first.org/epss/","probability":0.00445,"percentile":0.39182,"date":"2026-11-13","checkedAt":"2026-11-14T08:50:32.355Z"},{"source":"GitHub Advisory Database","id":"GHSA-2vgm-9qpx-xwqx","url":"https://github.com/advisories/GHSA-2vgm-9qpx-xwqx","modified":"2026-11-13T12:31:49Z","score":7,"vector":"CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:L/I:H/A:L","checkedAt":"2026-11-14T09:00:31.401Z"}],"aiSummary":{"text":"ExcelJS through 4.4.0 has a prototype pollution vulnerability via x14 Conditional Formatting Rule ID, allowing attackers to modify Object.prototype. Attackers can craft an xlsx file to set properties on every object.","model":"@cf/meta/llama-3.3-70b-instruct-fp8-fast","generatedAt":"2026-11-14T03:36:01.810Z","sources":[{"name":"CVE","url":"https://www.cve.org/CVERecord?id=CVE-2026-128337"}]}}