{
  "affected": [
    {
      "ranges": [
        {
          "database_specific": {
            "extracted_events": [
              {
                "range": [
                  {
                    "introduced": "0"
                  },
                  {
                    "last_affected": "4.4.0"
                  }
                ],
                "source": "AFFECTED_FIELD",
                "strategy": "StandardRange"
              }
            ]
          },
          "events": [
            {
              "introduced": "0"
            },
            {
              "last_affected": "ac96f9a61e9799c7776bd940f05c4a51d7200209"
            }
          ],
          "repo": "https://github.com/exceljs/exceljs",
          "type": "GIT"
        }
      ]
    }
  ],
  "aliases": [
    "GHSA-pwgq-2cgg-6ph9"
  ],
  "database_specific": {
    "cna_assigner": "VulnCheck",
    "cwe_ids": [
      "CWE-1321"
    ],
    "osv_generated_from": "https://github.com/CVEProject/cvelistV5/tree/main/cves/2026/128xxx/CVE-2026-128336.json"
  },
  "details": "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",
  "modified": "2026-11-14T02:30:41.558141451Z",
  "published": "2026-11-13T09:33:38.327Z",
  "references": [
    {
      "type": "ADVISORY",
      "url": "https://github.com/CVEProject/cvelistV5/tree/main/cves/2026/128xxx/CVE-2026-128336.json"
    },
    {
      "type": "PACKAGE",
      "url": "https://github.com/exceljs/exceljs"
    },
    {
      "type": "ARTICLE",
      "url": "https://github.com/exceljs/exceljs/blob/v4.4.0/lib/doc/defined-names.js#L182-L193"
    },
    {
      "type": "ARTICLE",
      "url": "https://github.com/exceljs/exceljs/blob/v4.4.0/lib/utils/cell-matrix.js#L50-L52"
    },
    {
      "type": "ADVISORY",
      "url": "https://github.com/mateocallec/exceljs-hardened/security/advisories/GHSA-pwgq-2cgg-6ph9"
    },
    {
      "type": "ADVISORY",
      "url": "https://nvd.nist.gov/vuln/detail/CVE-2026-128336"
    },
    {
      "type": "ADVISORY",
      "url": "https://www.vulncheck.com/advisories/exceljs-through-4.4.0-prototype-pollution-via-proto-defined-name"
    }
  ],
  "schema_version": "1.9.2",
  "severity": [
    {
      "score": "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",
      "type": "CVSS_V4"
    }
  ],
  "summary": "ExcelJS through 4.4.0 Prototype Pollution via __proto__ Defined Name"
}