fsspec: Server-Side Template Injection in ReferenceFileSystem leads to Remote Code Execution

{
  "id": "7fae96110bff87b0ff32191cf7c1d05018ea2eee5f9fb507c2b9750f6a113400",
  "url": "https://osv.dev/vulnerability/CVE-2026-104851",
  "method": "structured",
  "payload": {
    "kind": "advisory",
    "title": "fsspec: Server-Side Template Injection in ReferenceFileSystem leads to Remote Code Execution",
    "summary": "fsspec is a specification and Python implementation framework for filesystem interfaces. From 0.9.0 until 2026.6.0, fsspec.implementations.reference.ReferenceFileSystem evaluates fields from Kerchunk reference JSON documents through unrestricted jinja2.Template(...).render(...) calls in _process_references1._render_jinja, _process_templates, and _process_gen in fsspec/implementations/reference.py. A document supplied inline or fetched from an attacker-controlled URL can provide template expressions that execute Python code when the reference filesystem is opened, including through consumers such as xarray, before referenced data is read. The _process_gen path is reached whenever a document includes a gen array, while the other paths depend on template-related options and values. This issue is fixed in version 2026.6.0.",
    "evidence": "osv:CVE-2026-104851",
    "products": [],
    "severity": "high",
    "structured": {
      "id": "CVE-2026-104851",
      "aliases": [
        "CVE-2026-104851",
        "GHSA-27vj-qcqg-25rc",
        "PYSEC-2026-4217"
      ],
      "metrics": [
        {
          "type": "CVSS_V3",
          "score": "CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:H/I:H/A:H"
        }
      ],
      "affected": [
        {
          "ranges": [
            {
              "repo": "https://github.com/fsspec/filesystem_spec",
              "type": "GIT",
              "events": [
                {
                  "introduced": "c7d996685de74d2e3dc7f68b3c4722842a6914bc"
                },
                {
                  "fixed": "a2457004d03e0312f715f90f58873de5ab195a37"
                },
                {
                  "fixed": "86438783f93b1398ef245b92f0e6063b445b611c"
                },
                {
                  "fixed": "a1c16ab3f07f354aa371c38f7b1b07ea7fd4c5c8"
                }
              ],
              "database_specific": {
                "extracted_events": [
                  {
                    "range": [
                      {
                        "introduced": "0.9.0"
                      },
                      {
                        "fixed": "2026.6.0"
                      }
                    ],
                    "source": "AFFECTED_FIELD",
                    "strategy": "StringRangeExpression"
                  },
                  {
                    "range": [
                      {
                        "fixed": "86438783f93b1398ef245b92f0e6063b445b611c"
                      }
                    ],
                    "source": "REFERENCES_COMMIT"
                  },
                  {
                    "range": [
                      {
                        "fixed": "a1c16ab3f07f354aa371c38f7b1b07ea7fd4c5c8"
                      }
                    ],
                    "source": "REFERENCES_COMMIT"
                  },
                  {
                    "range": [
                      {
                        "fixed": "a2457004d03e0312f715f90f58873de5ab195a37"
                      }
                    ],
                    "source": "REFERENCES_TAG",
                    "original_tag": "2026.6.0"
                  }
                ]
              }
            }
          ],
          "versions": [
            "2026.4.0",
            "2026.3.0",
            "2026.2.0",
            "2026.1.0",
            "2025.12.0",
            "2025.10.0",
            "2025.9.0",
            "2025.7.0",
            "2025.5.1",
            "2025.5.0",
            "2025.3.2",
            "2025.3.1",
            "2025.3.0",
            "2025.2.0",
            "2024.12.0",
            "2024.10.0",
            "2024.9.0",
            "2024.6.1",
            "2024.6.0",
            "2024.5.0",
            "2024.3.1",
            "2024.3.0",
            "2024.2.0",
            "2023.12.2",
            "2023.12.1",
            "2023.12.0",
            "2023.10.0",
            "2023.9.2",
            "2023.9.1",
            "2023.9.0",
            "2023.6.0",
            "2023.5.0",
            "2023.4.0",
            "2023.3.0",
            "2023.1.0",
            "2022.11.0",
            "2022.10.0",
            "2022.8.2",
            "2022.8.1",
            "2022.8.0",
            "2022.7.1",
            "2022.7.0",
            "2022.5.0",
            "2022.3.0",
            "2022.02.0",
            "2022.01.0",
            "2021.11.1",
            "2021.11.0",
            "2021.10.1",
            "2021.10.0",
            "2021.09.0",
            "2021.08.1",
            "2021.07.0",
            "2021.06.1",
            "2021.06.0",
            "2021.05.0",
            "2021.04.0",
            "0.9.0"
          ],
          "database_specific": {
            "source": "https://storage.googleapis.com/cve-osv-conversion/osv-output/CVE-2026-104851.json"
          }
        }
      ],
      "modified": "2026-10-28T02:30:31.524422611Z",
      "provider": "osv",
      "references": [
        "https://github.com/fsspec/filesystem_spec/releases/tag/2026.6.0",
        "https://github.com/CVEProject/cvelistV5/tree/main/cves/2026/104xxx/CVE-2026-104851.json",
        "https://github.com/fsspec/filesystem_spec/security/advisories/GHSA-27vj-qcqg-25rc",
        "https://nvd.nist.gov/vuln/detail/CVE-2026-104851",
        "https://github.com/fsspec/filesystem_spec/commit/86438783f93b1398ef245b92f0e6063b445b611c",
        "https://github.com/fsspec/filesystem_spec/commit/a1c16ab3f07f354aa371c38f7b1b07ea7fd4c5c8",
        "https://github.com/fsspec/filesystem_spec/pull/2029",
        "https://github.com/fsspec/filesystem_spec/pull/2039"
      ],
      "provider_metadata": {
        "cwe_ids": [
          "CWE-1336",
          "CWE-94"
        ],
        "cna_assigner": "GitHub_M",
        "osv_generated_from": "https://github.com/CVEProject/cvelistV5/tree/main/cves/2026/104xxx/CVE-2026-104851.json"
      }
    },
    "related_cves": [
      {
        "value": "CVE-2026-104851",
        "evidence": "/id"
      }
    ],
    "security_relevant": true,
    "severity_evidence": "/severity/0/score"
  },
  "source_id": "core-osv",
  "document_id": 498539,
  "published_at": "2026-10-02T16:36:48.513+00:00"
}