# CVE-2026-104851: fsspec: fsspec is a specification and Python implementation framework for filesystem interfaces

CVE-2026-104851 is fixed in 2 products on 1 platform, first by OPENSUSE-SU-2026:22028-1, released October 6, 2026. It is not reported as exploited. Patch Radar priority: High.

- Web page: https://patchblox.com/security/cve/CVE-2026-104851
- Priority: High
- CVSS: 8.8 (high)
- EPSS: 0.0048
- CISA KEV: not listed
- Exploited (vendor report): no
- Publicly disclosed: no
- Published: Oct 2, 2026

## Description

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.

## Where it's fixed

| Platform | Product | Fixed in | Fix | Released |
|---|---|---|---|---|
| Linux | fsspec Debian 14 | 2026.9.0-1 | [DEBIAN-CVE-2026-104851](https://patchblox.com/security/data/fix/linux/debian-cve-2026-104851.md) | Oct 13, 2026 |
| Linux | python-fsspec opensuse-leap 16.0 | 2024.3.1-bp160.2.1 | [OPENSUSE-SU-2026:22028-1](https://patchblox.com/security/data/fix/linux/opensuse-su-2026-22028-1.md) | Oct 6, 2026 |

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Data as of 2026-11-10T07:50:38Z UTC. Source: Patchblox Patch Radar (https://patchblox.com/security/patch-radar). Patchblox finds out-of-date software on Windows, macOS and Linux and updates it through release rings: https://patchblox.com/demo

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