fsspec: Server-Side Template Injection in ReferenceFileSystem leads to Remote Code Execution (fsspec filesystem_spec)
At a glance
- Source
- NVD
- EPSS
- EPSS 0.47 % · percentile 41 ()
- State
- PUBLISHED
- Published
- Updated
- Assigner
- GitHub_M
- NVD status
- Deferred
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.
Weaknesses (CWE)
- CWE-94 — Improper Control of Generation of Code
- CWE-1336 — Improper Neutralization of Special Elements Used in a Template Engine
References
- https://github.com/fsspec/filesystem_spec/security/advisories/GHSA-27vj-qcqg-25rc
- https://github.com/fsspec/filesystem_spec/pull/2029
- https://github.com/fsspec/filesystem_spec/pull/2039
- https://github.com/fsspec/filesystem_spec/commit/86438783f93b1398ef245b92f0e6063b445b611c
- https://github.com/fsspec/filesystem_spec/commit/a1c16ab3f07f354aa371c38f7b1b07ea7fd4c5c8
- https://github.com/fsspec/filesystem_spec/releases/tag/2026.6.0
Scores
| Version | Score | Vector | Scored by |
|---|---|---|---|
| CVSS 3.1 | HIGH 8.8 | CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:H/I:H/A:H | GitHub_M |
| CVSS 3.1 | HIGH 8.8 | CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:H/I:H/A:H | NVD · security-advisories@github.com (Secondary) |
Advisories
- GHSA-27vj-qcqg-25rc — fsspec: Server-Side Template Injection in ReferenceFileSystem leads to Remote Code Execution
- PYSEC-2026-4217 — fsspec: Server-Side Template Injection in ReferenceFileSystem leads to Remote Code Execution
European references
- ENISA EUVD · EUVD-2026-91720
- GCVE · GCVE-0-2026-104851
CERT-FR advisories
- CERTFR-2026-AVI-1385 — Multiples vulnérabilités dans les produits VMware · cert.ssi.gouv.fr
Affected products
| Product | Versions |
|---|---|
| fsspec · filesystem_spec | affected >= 0.9.0, < 2026.6.0 |
Sources
| Source | Licence |
|---|---|
| CVE List (CVEProject cvelistV5) | CVE Program Terms of Use |
| EPSS (FIRST.org) | FIRST — attribution requested |
| ENISA EUVD | ENISA — reproduction authorised, source acknowledged |
| CERT-FR (ANSSI) | Licence Ouverte / Etalab 2.0 |
| NVD (NIST) via fkie-cad/nvd-json-data-feeds | Public domain — this product uses data from the NVD API but is not endorsed or certified by the NVD |