{"dataType": "CVE_RECORD", "dataVersion": "5.2", "cveMetadata": {"cveId": "CVE-2026-78207", "assignerOrgId": "83251b91-4cc7-4094-a5c7-464a1b83ea10", "state": "PUBLISHED", "assignerShortName": "VulnCheck", "dateReserved": "2026-08-24T00:15:01.656Z", "datePublished": "2026-08-24T00:30:47.125Z", "dateUpdated": "2026-08-24T00:30:47.125Z"}, "containers": {"cna": {"providerMetadata": {"orgId": "83251b91-4cc7-4094-a5c7-464a1b83ea10", "shortName": "VulnCheck", "dateUpdated": "2026-08-24T00:30:47.125Z"}, "datePublic": "2026-08-23T00:00:00.000Z", "title": "exceljs through 4.4.0 Prototype Pollution via deepMerge Reached From Note Serialization", "descriptions": [{"lang": "en", "value": "exceljs-hardened before 5.0.0 contains a prototype pollution vulnerability in the deepMerge helper that fails to reject __proto__, constructor, or prototype keys when merging note objects. Attackers can assign parsed JSON with a malicious __proto__ property to cell notes, modifying Object.prototype and affecting all plain objects created in the process."}], "problemTypes": [{"descriptions": [{"lang": "en", "description": "Improperly Controlled Modification of Object Prototype Attributes ('Prototype Pollution')", "cweId": "CWE-1321", "type": "CWE"}]}], "affected": [{"vendor": "exceljs", "product": "exceljs", "collectionURL": "https://www.npmjs.com/package/exceljs", "packageName": "exceljs", "packageURL": "pkg:npm/exceljs", "defaultStatus": "unaffected", "versions": [{"version": "0", "lessThanOrEqual": "4.4.0", "status": "affected", "versionType": "semver"}]}], "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:L/AT:N/PR:N/UI:N/VC:H/VI:H/VA:L/SC:N/SI:N/SA:N", "attackVector": "NETWORK", "attackComplexity": "LOW", "attackRequirements": "NONE", "privilegesRequired": "NONE", "userInteraction": "NONE", "vulnConfidentialityImpact": "HIGH", "vulnIntegrityImpact": "HIGH", "vulnAvailabilityImpact": "LOW", "subConfidentialityImpact": "NONE", "subIntegrityImpact": "NONE", "subAvailabilityImpact": "NONE", "baseScore": 9.3, "baseSeverity": "CRITICAL"}}, {"format": "CVSS", "cvssV3_1": {"version": "3.1", "vectorString": "CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:L", "attackVector": "NETWORK", "attackComplexity": "LOW", "privilegesRequired": "NONE", "userInteraction": "NONE", "scope": "UNCHANGED", "confidentialityImpact": "HIGH", "integrityImpact": "HIGH", "availabilityImpact": "LOW", "baseScore": 9.4, "baseSeverity": "CRITICAL"}}], "references": [{"url": "https://github.com/exceljs/exceljs", "tags": ["product"]}, {"url": "https://github.com/mateocallec/exceljs-hardened/security/advisories/GHSA-qwr4-7h29-chpf", "tags": ["third-party-advisory"]}, {"url": "https://github.com/exceljs/exceljs/blob/v4.4.0/lib/utils/under-dash.js#L155-L181", "tags": ["technical-description"]}, {"name": "VulnCheck Advisory: exceljs through 4.4.0 Prototype Pollution via deepMerge Reached From Note Serialization", "tags": ["third-party-advisory"], "url": "https://www.vulncheck.com/advisories/exceljs-through-prototype-pollution-via-deepmerge-reached-from-note-serialization"}], "credits": [{"lang": "en", "value": "Mat\u00e9o Florian Callec", "type": "finder"}], "x_generator": {"engine": "vulncheck-endgame"}}}}

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{"affected": [{"configurations": [{"platform": null, "status": "affected", "versions": {"scheme": "semver", "value": "[0,4.4.0]"}}], "enrichment": {"confidence": 95.0, "confidence_source": "inferred", "scores": [{"score": 95.0, "source": "inferred"}, {"score": 100.0, "source": "matching"}]}, "original": {"product": "exceljs", "source": "cna", "vendor": "exceljs"}, "product": "exceljs", "vendor": "exceljs_project"}], "created": "2026-08-24T01:30:04.791743+00:00", "updated": "2026-08-24T02:30:10.675014+00:00", "vendors": ["exceljs_project", "exceljs_project$PRODUCT$exceljs"]}