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.
Published: 2026-10-02
Score: 8.8 High
EPSS: < 1% Very Low
KEV: No
Impact: n/a
Action: n/a
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Remediation

No vendor fix or workaround currently provided.

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Tracking

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Advisories
Source ID Title
Github GHSA Github GHSA GHSA-27vj-qcqg-25rc fsspec: Server-Side Template Injection in ReferenceFileSystem leads to Remote Code Execution
History

Mon, 05 Oct 2026 21:30:00 +0000

Type Values Removed Values Added
Metrics ssvc

{'options': {'Automatable': 'no', 'Exploitation': 'poc', 'Technical Impact': 'total'}, 'version': '2.0.3'}


Sun, 04 Oct 2026 22:15:00 +0000

Type Values Removed Values Added
First Time appeared Fsspec
Fsspec filesystem Spec
Vendors & Products Fsspec
Fsspec filesystem Spec

Sat, 03 Oct 2026 00:30:00 +0000

Type Values Removed Values Added
References
Metrics threat_severity

None

threat_severity

Important


Fri, 02 Oct 2026 16:45:00 +0000

Type Values Removed Values Added
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.
Title fsspec: Server-Side Template Injection in ReferenceFileSystem leads to Remote Code Execution
Weaknesses CWE-1336
CWE-94
References
Metrics cvssV3_1

{'score': 8.8, 'vector': 'CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:H/I:H/A:H'}


Subscriptions

Fsspec Filesystem Spec
cve-icon MITRE

Status: PUBLISHED

Assigner: GitHub_M

Published:

Updated: 2026-10-05T20:03:36.502Z

Reserved: 2026-10-02T14:38:43.244Z

Link: CVE-2026-104851

cve-icon Vulnrichment

Updated: 2026-10-05T20:03:16.024Z

cve-icon NVD

Status : Deferred

Published: 2026-10-02T17:17:03.763

Modified: 2026-10-05T20:17:09.373

Link: CVE-2026-104851

cve-icon Redhat

Severity : Important

Publid Date: 2026-10-02T16:36:48Z

Links: CVE-2026-104851 - Bugzilla

cve-icon OpenCVE Enrichment

Updated: 2026-10-04T20:53:34Z

Weaknesses