CVE-2026-104851

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

Published Oct 2, 2026 CVSS 3.1 · 8.8 High EPSS < 1% KEV · Not listed
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.

Remediation

No solution or workaround provided in the CVE record

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
Type Values Removed Values Added
Metrics ssvc

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

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

Weaknesses

Sources

Status
PUBLISHED
Assigner
GitHub_M
Published
Updated
Oct 5, 2026, 8:03 PM
Reserved
Oct 2, 2026, 2:38 PM
Status
Deferred
Published
Oct 2, 2026, 5:17 PM
Modified
Oct 5, 2026, 8:17 PM
Severity
Important
Public date
Oct 2, 2026, 4:36 PM