{"dataType": "CVE_RECORD", "dataVersion": "5.2", "cveMetadata": {"cveId": "CVE-2026-128336", "assignerOrgId": "83251b91-4cc7-4094-a5c7-464a1b83ea10", "state": "PUBLISHED", "assignerShortName": "VulnCheck", "dateReserved": "2026-11-13T01:20:38.540Z", "datePublished": "2026-11-13T09:33:38.327Z", "dateUpdated": "2026-11-13T09:33:38.327Z"}, "containers": {"cna": {"providerMetadata": {"orgId": "83251b91-4cc7-4094-a5c7-464a1b83ea10", "shortName": "VulnCheck", "dateUpdated": "2026-11-13T09:33:38.327Z"}, "datePublic": "2026-10-16T00:00:00.000Z", "title": "ExcelJS through 4.4.0 Prototype Pollution via __proto__ Defined Name", "descriptions": [{"lang": "en", "value": "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."}], "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:N/VI:L/VA:L/SC:N/SI:N/SA:N", "attackVector": "NETWORK", "attackComplexity": "HIGH", "attackRequirements": "PRESENT", "privilegesRequired": "NONE", "userInteraction": "NONE", "vulnConfidentialityImpact": "NONE", "vulnIntegrityImpact": "LOW", "vulnAvailabilityImpact": "LOW", "subConfidentialityImpact": "NONE", "subIntegrityImpact": "NONE", "subAvailabilityImpact": "NONE", "baseScore": 6.3, "baseSeverity": "MEDIUM"}}, {"format": "CVSS", "cvssV3_1": {"version": "3.1", "vectorString": "CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:N/I:L/A:L", "attackVector": "NETWORK", "attackComplexity": "HIGH", "privilegesRequired": "NONE", "userInteraction": "NONE", "scope": "UNCHANGED", "confidentialityImpact": "NONE", "integrityImpact": "LOW", "availabilityImpact": "LOW", "baseScore": 4.8, "baseSeverity": "MEDIUM"}}], "references": [{"url": "https://github.com/exceljs/exceljs", "tags": ["product"]}, {"url": "https://github.com/mateocallec/exceljs-hardened/security/advisories/GHSA-pwgq-2cgg-6ph9", "tags": ["third-party-advisory"], "name": "GitHub Security Advisory (GHSA-pwgq-2cgg-6ph9)"}, {"url": "https://github.com/exceljs/exceljs/blob/v4.4.0/lib/utils/cell-matrix.js#L50-L52", "tags": ["technical-description"]}, {"url": "https://github.com/exceljs/exceljs/blob/v4.4.0/lib/doc/defined-names.js#L182-L193", "tags": ["technical-description"]}, {"name": "VulnCheck Advisory: ExcelJS through 4.4.0 Prototype Pollution via __proto__ Defined Name", "tags": ["third-party-advisory"], "url": "https://www.vulncheck.com/advisories/exceljs-through-4.4.0-prototype-pollution-via-proto-defined-name"}], "credits": [{"lang": "en", "value": "Mat\u00e9o Florian Callec", "type": "finder"}], "x_generator": {"engine": "vulncheck-endgame"}}}}

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