{
  "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-86ch-m4gp-r5xf"
  ],
  "database_specific": {
    "cna_assigner": "VulnCheck",
    "cwe_ids": [
      "CWE-1321"
    ],
    "osv_generated_from": "https://github.com/CVEProject/cvelistV5/tree/main/cves/2026/128xxx/CVE-2026-128337.json"
  },
  "details": "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.",
  "id": "CVE-2026-128337",
  "modified": "2026-11-14T02:30:57.041066823Z",
  "published": "2026-11-13T09:33:37.679Z",
  "references": [
    {
      "type": "ADVISORY",
      "url": "https://github.com/CVEProject/cvelistV5/tree/main/cves/2026/128xxx/CVE-2026-128337.json"
    },
    {
      "type": "PACKAGE",
      "url": "https://github.com/exceljs/exceljs"
    },
    {
      "type": "ARTICLE",
      "url": "https://github.com/exceljs/exceljs/blob/v4.4.0/lib/xlsx/xform/sheet/worksheet-xform.js#L34-L42"
    },
    {
      "type": "ARTICLE",
      "url": "https://github.com/exceljs/exceljs/blob/v4.4.0/lib/xlsx/xform/sheet/worksheet-xform.js#L55-L74"
    },
    {
      "type": "ADVISORY",
      "url": "https://github.com/mateocallec/exceljs-hardened/security/advisories/GHSA-86ch-m4gp-r5xf"
    },
    {
      "type": "ADVISORY",
      "url": "https://nvd.nist.gov/vuln/detail/CVE-2026-128337"
    },
    {
      "type": "ADVISORY",
      "url": "https://www.vulncheck.com/advisories/exceljs-through-4.4.0-prototype-pollution-via-x14-conditional-formatting-rule-id"
    }
  ],
  "schema_version": "1.9.2",
  "severity": [
    {
      "score": "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",
      "type": "CVSS_V4"
    }
  ],
  "summary": "ExcelJS through 4.4.0 Prototype Pollution via x14 Conditional Formatting Rule ID"
}