---
id: CVE-2026-104851
title: >-
  fsspec is a specification and Python implementation framework for filesystem
  interfaces
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 unre…
severity: high
cvss: 8.8
cvssVector: 'CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:H/I:H/A:H'
cwe:
  - CWE-94
  - CWE-1336
vendor: fsspec
product: filesystem_spec
affected:
  - 'filesystem_spec >= 0.9.0, < 2026.6.0'
published: '2026-10-02'
updated: '2026-10-02'
sourceUpdated: '2026-10-02T17:17:03.763'
source: NVD
sourceUrl: 'https://nvd.nist.gov/vuln/detail/CVE-2026-104851'
references:
  - url: >-
      https://github.com/fsspec/filesystem_spec/commit/86438783f93b1398ef245b92f0e6063b445b611c
    label: security-advisories@github.com
  - url: >-
      https://github.com/fsspec/filesystem_spec/commit/a1c16ab3f07f354aa371c38f7b1b07ea7fd4c5c8
    label: security-advisories@github.com
  - url: 'https://github.com/fsspec/filesystem_spec/pull/2029'
    label: security-advisories@github.com
  - url: 'https://github.com/fsspec/filesystem_spec/pull/2039'
    label: security-advisories@github.com
  - url: 'https://github.com/fsspec/filesystem_spec/releases/tag/2026.6.0'
    label: security-advisories@github.com
  - url: >-
      https://github.com/fsspec/filesystem_spec/security/advisories/GHSA-27vj-qcqg-25rc
    label: security-advisories@github.com
tags:
  - nvd
  - cve.org
ingestedAt: '2026-10-02T17:24:03.905Z'
---

## Overview

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.

## Remediation

Refer to the linked advisories for vendor-supplied fixes and affected version ranges.