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[ CVE-2026-104851 · Published 2 Oct 2026 ]

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

CVSS 8.8 EPSS <1%1 agency advisoryFix available

[ Why it matters ]Priority signals

  • Public proof-of-concept exploit exists (CISA SSVC)

[ Description ]Official 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.

[ Fixes ]Fixes and patches

  • fsspec 2026.6.0Fixed version · GitHub Advisories · pip package fsspec: upgrade to 2026.6.0 or later (affected >= 0.9.0, < 2026.6.0)

[ Advisories ]Government CERT advisories

[ Packages ]Affected open-source packages

[ References ]References