CVE-2026-128336

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{"affected": [{"affectedData": [{"defaultStatus": "unaffected", "packageURL": "pkg:npm/exceljs", "product": "exceljs", "vendor": "exceljs", "versions": [{"lessThanOrEqual": "4.4.0", "status": "affected", "version": "0", "versionType": "semver"}]}], "source": "disclosure@vulncheck.com"}], "cveTags": [], "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."}], "id": "CVE-2026-128336", "lastModified": "2026-11-13T10:18:13.757", "metrics": {"cvssMetricV31": [{"cvssData": {"attackComplexity": "HIGH", "attackVector": "NETWORK", "availabilityImpact": "LOW", "baseScore": 4.8, "baseSeverity": "MEDIUM", "confidentialityImpact": "NONE", "integrityImpact": "LOW", "privilegesRequired": "NONE", "scope": "UNCHANGED", "userInteraction": "NONE", "vectorString": "CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:N/I:L/A:L", "version": "3.1"}, "exploitabilityScore": 2.2, "impactScore": 2.5, "source": "disclosure@vulncheck.com", "type": "Primary"}], "cvssMetricV40": [{"cvssData": {"Automatable": "NOT_DEFINED", "Recovery": "NOT_DEFINED", "Safety": "NOT_DEFINED", "attackComplexity": "HIGH", "attackRequirements": "PRESENT", "attackVector": "NETWORK", "availabilityRequirement": "NOT_DEFINED", "baseScore": 6.3, "baseSeverity": "MEDIUM", "confidentialityRequirement": "NOT_DEFINED", "exploitMaturity": "NOT_DEFINED", "integrityRequirement": "NOT_DEFINED", "modifiedAttackComplexity": "NOT_DEFINED", "modifiedAttackRequirements": "NOT_DEFINED", "modifiedAttackVector": "NOT_DEFINED", "modifiedPrivilegesRequired": "NOT_DEFINED", "modifiedSubAvailabilityImpact": "NOT_DEFINED", "modifiedSubConfidentialityImpact": "NOT_DEFINED", "modifiedSubIntegrityImpact": "NOT_DEFINED", "modifiedUserInteraction": "NOT_DEFINED", "modifiedVulnAvailabilityImpact": "NOT_DEFINED", "modifiedVulnConfidentialityImpact": "NOT_DEFINED", "modifiedVulnIntegrityImpact": "NOT_DEFINED", "privilegesRequired": "NONE", "providerUrgency": "NOT_DEFINED", "subAvailabilityImpact": "NONE", "subConfidentialityImpact": "NONE", "subIntegrityImpact": "NONE", "userInteraction": "NONE", "valueDensity": "NOT_DEFINED", "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/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", "vulnAvailabilityImpact": "LOW", "vulnConfidentialityImpact": "NONE", "vulnIntegrityImpact": "LOW", "vulnerabilityResponseEffort": "NOT_DEFINED"}, "source": "disclosure@vulncheck.com", "type": "Secondary"}]}, "published": "2026-11-13T10:18:13.757", "references": [{"source": "disclosure@vulncheck.com", "url": "https://github.com/exceljs/exceljs"}, {"source": "disclosure@vulncheck.com", "url": "https://github.com/exceljs/exceljs/blob/v4.4.0/lib/doc/defined-names.js#L182-L193"}, {"source": "disclosure@vulncheck.com", "url": "https://github.com/exceljs/exceljs/blob/v4.4.0/lib/utils/cell-matrix.js#L50-L52"}, {"source": "disclosure@vulncheck.com", "url": "https://github.com/mateocallec/exceljs-hardened/security/advisories/GHSA-pwgq-2cgg-6ph9"}, {"source": "disclosure@vulncheck.com", "url": "https://www.vulncheck.com/advisories/exceljs-through-4.4.0-prototype-pollution-via-proto-defined-name"}], "sourceIdentifier": "disclosure@vulncheck.com", "vulnStatus": "Received", "weaknesses": [{"description": [{"lang": "en", "value": "CWE-1321"}], "source": "disclosure@vulncheck.com", "type": "Primary"}]}

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