{"dataType":"CVE_RECORD","dataVersion":"5.2","cveMetadata":{"cveId":"CVE-2026-128337","assignerOrgId":"83251b91-4cc7-4094-a5c7-464a1b83ea10","state":"PUBLISHED","assignerShortName":"VulnCheck","dateReserved":"2026-11-13T01:20:39.850Z","datePublished":"2026-11-13T09:33:37.679Z","dateUpdated":"2026-11-13T09:33:37.679Z"},"containers":{"cna":{"providerMetadata":{"orgId":"83251b91-4cc7-4094-a5c7-464a1b83ea10","shortName":"VulnCheck","dateUpdated":"2026-11-13T09:33:37.679Z"},"datePublic":"2026-10-16T00:00:00.000Z","title":"ExcelJS through 4.4.0 Prototype Pollution via x14 Conditional Formatting Rule ID","descriptions":[{"lang":"en","value":"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."}],"problemTypes":[{"descriptions":[{"lang":"en","description":"Improperly Controlled Modification of Object Prototype Attributes ('Prototype Pollution')","cweId":"CWE-1321","type":"CWE"}]}],"affected":[{"vendor":"exceljs","product":"exceljs","defaultStatus":"unaffected","versions":[{"version":"0","status":"affected","versionType":"semver","lessThanOrEqual":"4.4.0"}],"packageURL":"pkg:npm/exceljs"}],"cpeApplicability":[{"nodes":[{"operator":"OR","negate":false,"cpeMatch":[{"vulnerable":true,"criteria":"cpe:2.3:a:exceljs_project:exceljs:*:*:*:*:*:*:*:*","versionEndIncluding":"4.4.0"}]}]}],"metrics":[{"format":"CVSS","cvssV4_0":{"version":"4.0","vectorString":"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","attackVector":"NETWORK","attackComplexity":"HIGH","attackRequirements":"PRESENT","privilegesRequired":"NONE","userInteraction":"NONE","vulnConfidentialityImpact":"LOW","vulnIntegrityImpact":"HIGH","vulnAvailabilityImpact":"LOW","subConfidentialityImpact":"NONE","subIntegrityImpact":"NONE","subAvailabilityImpact":"NONE","baseScore":8.3,"baseSeverity":"HIGH"}},{"format":"CVSS","cvssV3_1":{"version":"3.1","vectorString":"CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:L/I:H/A:L","attackVector":"NETWORK","attackComplexity":"HIGH","privilegesRequired":"NONE","userInteraction":"NONE","scope":"UNCHANGED","confidentialityImpact":"LOW","integrityImpact":"HIGH","availabilityImpact":"LOW","baseScore":7,"baseSeverity":"HIGH"}}],"references":[{"url":"https://github.com/exceljs/exceljs","tags":["product"]},{"url":"https://github.com/mateocallec/exceljs-hardened/security/advisories/GHSA-86ch-m4gp-r5xf","tags":["third-party-advisory"],"name":"GitHub Security Advisory (GHSA-86ch-m4gp-r5xf)"},{"url":"https://github.com/exceljs/exceljs/blob/v4.4.0/lib/xlsx/xform/sheet/worksheet-xform.js#L34-L42","tags":["technical-description"]},{"url":"https://github.com/exceljs/exceljs/blob/v4.4.0/lib/xlsx/xform/sheet/worksheet-xform.js#L55-L74","tags":["technical-description"]},{"name":"VulnCheck Advisory: ExcelJS through 4.4.0 Prototype Pollution via x14 Conditional Formatting Rule ID","tags":["third-party-advisory"],"url":"https://www.vulncheck.com/advisories/exceljs-through-4.4.0-prototype-pollution-via-x14-conditional-formatting-rule-id"}],"credits":[{"lang":"en","value":"Matéo Florian Callec","type":"finder"}],"x_generator":{"engine":"vulncheck-endgame"}}}}