CVE-2026-104851 (GCVE-0-2026-104851)

Vulnerability from cvelistv5 – Published: 2026-10-02 16:36 – Updated: 2026-10-02 16:36
VLAI
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.
Severity
8.8 (High)
CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:H/I:H/A:H
CWE
  • CWE-94 - Improper Control of Generation of Code ('Code Injection')
  • CWE-1336 - Improper Neutralization of Special Elements Used in a Template Engine
Assigner
References
Impacted products
Vendor Product Version CPE status
fsspec filesystem_spec Affected: >= 0.9.0, < 2026.6.0
guessed Create a notification for this product.
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{
  "containers": {
    "cna": {
      "affected": [
        {
          "product": "filesystem_spec",
          "vendor": "fsspec",
          "versions": [
            {
              "status": "affected",
              "version": "\u003e= 0.9.0, \u003c 2026.6.0"
            }
          ]
        }
      ],
      "descriptions": [
        {
          "lang": "en",
          "value": "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."
        }
      ],
      "metrics": [
        {
          "cvssV3_1": {
            "attackComplexity": "LOW",
            "attackVector": "NETWORK",
            "availabilityImpact": "HIGH",
            "baseScore": 8.8,
            "baseSeverity": "HIGH",
            "confidentialityImpact": "HIGH",
            "integrityImpact": "HIGH",
            "privilegesRequired": "NONE",
            "scope": "UNCHANGED",
            "userInteraction": "REQUIRED",
            "vectorString": "CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:H/I:H/A:H",
            "version": "3.1"
          }
        }
      ],
      "problemTypes": [
        {
          "descriptions": [
            {
              "cweId": "CWE-94",
              "description": "CWE-94: Improper Control of Generation of Code (\u0027Code Injection\u0027)",
              "lang": "en",
              "type": "CWE"
            }
          ]
        },
        {
          "descriptions": [
            {
              "cweId": "CWE-1336",
              "description": "CWE-1336: Improper Neutralization of Special Elements Used in a Template Engine",
              "lang": "en",
              "type": "CWE"
            }
          ]
        }
      ],
      "providerMetadata": {
        "dateUpdated": "2026-10-02T16:36:48.513Z",
        "orgId": "a0819718-46f1-4df5-94e2-005712e83aaa",
        "shortName": "GitHub_M"
      },
      "references": [
        {
          "name": "https://github.com/fsspec/filesystem_spec/security/advisories/GHSA-27vj-qcqg-25rc",
          "tags": [
            "x_refsource_CONFIRM"
          ],
          "url": "https://github.com/fsspec/filesystem_spec/security/advisories/GHSA-27vj-qcqg-25rc"
        },
        {
          "name": "https://github.com/fsspec/filesystem_spec/pull/2029",
          "tags": [
            "x_refsource_MISC"
          ],
          "url": "https://github.com/fsspec/filesystem_spec/pull/2029"
        },
        {
          "name": "https://github.com/fsspec/filesystem_spec/pull/2039",
          "tags": [
            "x_refsource_MISC"
          ],
          "url": "https://github.com/fsspec/filesystem_spec/pull/2039"
        },
        {
          "name": "https://github.com/fsspec/filesystem_spec/commit/86438783f93b1398ef245b92f0e6063b445b611c",
          "tags": [
            "x_refsource_MISC"
          ],
          "url": "https://github.com/fsspec/filesystem_spec/commit/86438783f93b1398ef245b92f0e6063b445b611c"
        },
        {
          "name": "https://github.com/fsspec/filesystem_spec/commit/a1c16ab3f07f354aa371c38f7b1b07ea7fd4c5c8",
          "tags": [
            "x_refsource_MISC"
          ],
          "url": "https://github.com/fsspec/filesystem_spec/commit/a1c16ab3f07f354aa371c38f7b1b07ea7fd4c5c8"
        },
        {
          "name": "https://github.com/fsspec/filesystem_spec/releases/tag/2026.6.0",
          "tags": [
            "x_refsource_MISC"
          ],
          "url": "https://github.com/fsspec/filesystem_spec/releases/tag/2026.6.0"
        }
      ],
      "source": {
        "advisory": "GHSA-27vj-qcqg-25rc",
        "discovery": "UNKNOWN"
      },
      "title": "fsspec: Server-Side Template Injection in ReferenceFileSystem leads to Remote Code Execution"
    }
  },
  "cveMetadata": {
    "assignerOrgId": "a0819718-46f1-4df5-94e2-005712e83aaa",
    "assignerShortName": "GitHub_M",
    "cveId": "CVE-2026-104851",
    "datePublished": "2026-10-02T16:36:48.513Z",
    "dateReserved": "2026-10-02T14:38:43.244Z",
    "dateUpdated": "2026-10-02T16:36:48.513Z",
    "state": "PUBLISHED"
  },
  "dataType": "CVE_RECORD",
  "dataVersion": "5.2",
  "vulnerability-lookup:meta": {
    "nvd": {
      "cve": {
        "affected": [
          {
            "affectedData": [
              {
                "product": "filesystem_spec",
                "vendor": "fsspec",
                "versions": [
                  {
                    "status": "affected",
                    "version": "\u003e= 0.9.0, \u003c 2026.6.0"
                  }
                ]
              }
            ],
            "source": "security-advisories@github.com"
          }
        ],
        "cveTags": [],
        "descriptions": [
          {
            "lang": "en",
            "value": "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."
          }
        ],
        "id": "CVE-2026-104851",
        "lastModified": "2026-10-02T18:47:49.947",
        "metrics": {
          "cvssMetricV31": [
            {
              "cvssData": {
                "attackComplexity": "LOW",
                "attackVector": "NETWORK",
                "availabilityImpact": "HIGH",
                "baseScore": 8.8,
                "baseSeverity": "HIGH",
                "confidentialityImpact": "HIGH",
                "integrityImpact": "HIGH",
                "privilegesRequired": "NONE",
                "scope": "UNCHANGED",
                "userInteraction": "REQUIRED",
                "vectorString": "CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:H/I:H/A:H",
                "version": "3.1"
              },
              "exploitabilityScore": 2.8,
              "impactScore": 5.9,
              "source": "security-advisories@github.com",
              "type": "Secondary"
            }
          ]
        },
        "published": "2026-10-02T17:17:03.763",
        "references": [
          {
            "source": "security-advisories@github.com",
            "url": "https://github.com/fsspec/filesystem_spec/commit/86438783f93b1398ef245b92f0e6063b445b611c"
          },
          {
            "source": "security-advisories@github.com",
            "url": "https://github.com/fsspec/filesystem_spec/commit/a1c16ab3f07f354aa371c38f7b1b07ea7fd4c5c8"
          },
          {
            "source": "security-advisories@github.com",
            "url": "https://github.com/fsspec/filesystem_spec/pull/2029"
          },
          {
            "source": "security-advisories@github.com",
            "url": "https://github.com/fsspec/filesystem_spec/pull/2039"
          },
          {
            "source": "security-advisories@github.com",
            "url": "https://github.com/fsspec/filesystem_spec/releases/tag/2026.6.0"
          },
          {
            "source": "security-advisories@github.com",
            "url": "https://github.com/fsspec/filesystem_spec/security/advisories/GHSA-27vj-qcqg-25rc"
          }
        ],
        "sourceIdentifier": "security-advisories@github.com",
        "vulnStatus": "Deferred",
        "weaknesses": [
          {
            "description": [
              {
                "lang": "en",
                "value": "CWE-94"
              },
              {
                "lang": "en",
                "value": "CWE-1336"
              }
            ],
            "source": "security-advisories@github.com",
            "type": "Primary"
          }
        ]
      }
    },
    "redhat_vex": {
      "aggregate_severity": "Important",
      "current_release_date": "2026-10-02T17:39:57+00:00",
      "cve": "CVE-2026-104851",
      "id": "CVE-2026-104851",
      "initial_release_date": "2026-10-02T16:36:48.513000+00:00",
      "product_status:known_affected": "90",
      "source": "Red Hat CSAF VEX",
      "status": "final",
      "title": "fsspec: fsspec: Arbitrary code execution via crafted reference documents",
      "url": "https://security.access.redhat.com/data/csaf/v2/vex/2026/cve-2026-104851.json",
      "version": "3"
    }
  }
}



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Forecast uses a logistic model when the trend is rising, or an exponential decay model when the trend is falling. Fitted via linearized least squares.

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Nomenclature

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Vulnerabilities whose description is nearest to this one in the vector space of the CIRCL/vulnerability-attack-technique-biencoder model. This is a similarity search over the bi-encoder space (plain cosine), not a classification, and it has no measured accuracy.