PhpSpreadsheet: XmlScanner Bypass via Double-Encoded unentity() TOCTOU Allows XXE and Denial of Service

{
  "id": "5af4b26433ed23a0861ed962460b30385ecb9efa93728c4f0df17ff9dbceacde",
  "url": "https://osv.dev/vulnerability/CVE-2026-108357",
  "method": "structured",
  "payload": {
    "kind": "advisory",
    "title": "PhpSpreadsheet: XmlScanner Bypass via Double-Encoded unentity() TOCTOU Allows XXE and Denial of Service",
    "summary": "PhpSpreadsheet is a pure PHP library for reading and writing spreadsheet files. From 3.3.0 until 3.10.8 and 5.10.0, Reader\\Xml passes stored SpreadsheetML XML through XmlScanner::scan in Xml::canRead and Xml::trySimpleXMLLoadStringPrivate, while Xml::unentity decodes numeric entities only after each DOCTYPE pattern check. A double-encoded less-than character is reduced by the first callback to another encoded character and by the second callback to a literal less-than sign, so SimpleXML receives an unchecked DOCTYPE and entity declaration. Processing attacker-controlled SpreadsheetML XML can cause entity-expansion denial of service and can permit local file access or SSRF on PHP before 8.0 or when LIBXML_NOENT is enabled. This issue is fixed in versions 3.10.8 and 5.10.0.",
    "evidence": "osv:CVE-2026-108357",
    "products": [],
    "severity": "high",
    "structured": {
      "id": "CVE-2026-108357",
      "aliases": [
        "CVE-2026-108357",
        "GHSA-rxj4-h86g-25gc"
      ],
      "metrics": [
        {
          "type": "CVSS_V4",
          "score": "CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:L/VI:N/VA:H/SC:L/SI:N/SA:N"
        }
      ],
      "affected": [
        {
          "ranges": [
            {
              "repo": "https://github.com/phpoffice/phpspreadsheet",
              "type": "GIT",
              "events": [
                {
                  "introduced": "87ddd21eb0b6b7ad20a11d314348ef307475f547"
                },
                {
                  "fixed": "fee9c1ca8d9f1f676f007ac1ab134ce43624bd52"
                },
                {
                  "introduced": "2d4b9f3582102aafb6b1378fff8a20eeeacfb31c"
                },
                {
                  "fixed": "eb18727acf6b1f4cc67145a52ab04f9fd4c28d53"
                },
                {
                  "fixed": "89f455c133e1a7e2d4abfadc43ce29eb7450d781"
                },
                {
                  "fixed": "980b5c294493856f1a25754f1e8a1d2185b93738"
                }
              ],
              "database_specific": {
                "extracted_events": [
                  {
                    "range": [
                      {
                        "introduced": "3.3.0"
                      },
                      {
                        "fixed": "3.10.8"
                      }
                    ],
                    "source": "AFFECTED_FIELD",
                    "strategy": "StringRangeExpression"
                  },
                  {
                    "range": [
                      {
                        "introduced": "4.0.0"
                      },
                      {
                        "fixed": "5.10.0"
                      }
                    ],
                    "source": "AFFECTED_FIELD",
                    "strategy": "StringRangeExpression"
                  },
                  {
                    "range": [
                      {
                        "fixed": "89f455c133e1a7e2d4abfadc43ce29eb7450d781"
                      }
                    ],
                    "source": "REFERENCES_COMMIT"
                  },
                  {
                    "range": [
                      {
                        "fixed": "980b5c294493856f1a25754f1e8a1d2185b93738"
                      }
                    ],
                    "source": "REFERENCES_COMMIT"
                  },
                  {
                    "range": [
                      {
                        "fixed": "fee9c1ca8d9f1f676f007ac1ab134ce43624bd52"
                      }
                    ],
                    "source": "REFERENCES_TAG",
                    "original_tag": "3.10.8"
                  },
                  {
                    "range": [
                      {
                        "fixed": "eb18727acf6b1f4cc67145a52ab04f9fd4c28d53"
                      }
                    ],
                    "source": "REFERENCES_TAG",
                    "original_tag": "5.10.0"
                  }
                ]
              }
            }
          ],
          "versions": [
            "5.9.0",
            "3.10.7",
            "3.10.6",
            "5.8.0",
            "3.10.5",
            "5.7.0",
            "5.6.0",
            "3.10.4",
            "5.5.0",
            "3.10.3",
            "5.4.0",
            "5.3.0",
            "3.10.2",
            "5.1.0",
            "5.2.0",
            "3.10.1",
            "3.10.0",
            "5.0.0",
            "3.9.3",
            "4.5.0",
            "3.9.2",
            "4.4.0",
            "4.3.0",
            "4.3.1",
            "4.2.0",
            "4.1.0",
            "3.3.0",
            "3.9.0",
            "3.9.1",
            "4.0.0",
            "3.8.0",
            "3.7.0",
            "3.6.0",
            "3.5.0",
            "3.4.0"
          ],
          "database_specific": {
            "source": "https://storage.googleapis.com/cve-osv-conversion/osv-output/CVE-2026-108357.json"
          }
        }
      ],
      "modified": "2026-10-28T02:30:32.926882887Z",
      "provider": "osv",
      "references": [
        "https://github.com/PHPOffice/PhpSpreadsheet/releases/tag/3.10.8",
        "https://github.com/PHPOffice/PhpSpreadsheet/releases/tag/5.10.0",
        "https://github.com/CVEProject/cvelistV5/tree/main/cves/2026/108xxx/CVE-2026-108357.json",
        "https://github.com/PHPOffice/PhpSpreadsheet/security/advisories/GHSA-rxj4-h86g-25gc",
        "https://nvd.nist.gov/vuln/detail/CVE-2026-108357",
        "https://github.com/PHPOffice/PhpSpreadsheet/commit/89f455c133e1a7e2d4abfadc43ce29eb7450d781",
        "https://github.com/PHPOffice/PhpSpreadsheet/commit/980b5c294493856f1a25754f1e8a1d2185b93738"
      ],
      "provider_metadata": {
        "cwe_ids": [
          "CWE-611",
          "CWE-776"
        ],
        "cna_assigner": "GitHub_M",
        "osv_generated_from": "https://github.com/CVEProject/cvelistV5/tree/main/cves/2026/108xxx/CVE-2026-108357.json"
      }
    },
    "related_cves": [
      {
        "value": "CVE-2026-108357",
        "evidence": "/id"
      }
    ],
    "security_relevant": true,
    "severity_evidence": "/severity/0/score"
  },
  "source_id": "core-osv",
  "document_id": 500162,
  "published_at": "2026-10-22T17:38:16.098+00:00"
}