{"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": "Mat\u00e9o Florian Callec", "type": "finder"}], "x_generator": {"engine": "vulncheck-endgame"}}}}

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