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

MITRE NVD CVE.ORG JSON API

Summary

CVECVE-2026-104851
StatePUBLISHED
AssignerGitHub_M
Source PriorityCVE Program / NVD first with legacy fallback
Published2026-10-02 17:17:03 UTC
Updated2026-10-02 18:47:49 UTC
Descriptionfsspec 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.

Risk And Classification

Primary CVSS: v3.1 8.8 HIGH from [email protected]

CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:H/I:H/A:H

Problem Types: CWE-94 | CWE-1336 | CWE-94 CWE-94: Improper Control of Generation of Code ('Code Injection') | CWE-1336 CWE-1336: Improper Neutralization of Special Elements Used in a Template Engine

VersionSourceTypeScoreSeverityVector
3.1[email protected]Secondary8.8HIGHCVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:H/I:H/A:H
3.1CNADECLARED8.8HIGHCVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:H/I:H/A:H

CVSS v3.1 Breakdown

Attack Vector
Network
Attack Complexity
Low
Privileges Required
None
User Interaction
Required
Scope
Unchanged
Confidentiality
High
Integrity
High
Availability
High

CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:H/I:H/A:H

Vendor Declared Affected Products

SourceVendorProductVersionPlatforms
CNA Fsspec Filesystem Spec affected >= 0.9.0, < 2026.6.0 Not specified

References

ReferenceSourceLinkTags
github.com/fsspec/filesystem_spec/releases/tag/2026.6.0 [email protected] github.com
github.com/fsspec/filesystem_spec/commit/a1c16ab3f07f354aa371c38f7b1b07e... [email protected] github.com
github.com/fsspec/filesystem_spec/pull/2029 [email protected] github.com
github.com/fsspec/filesystem_spec/pull/2039 [email protected] github.com
github.com/fsspec/filesystem_spec/commit/86438783f93b1398ef245b92f0e6063... [email protected] github.com
github.com/fsspec/filesystem_spec/security/advisories/GHSA-27vj-qcqg-25rc [email protected] github.com
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