filesystem_spec up to 2026.5.x ReferenceFileSystem reference.py special elements in template engine

CVSS Meta Temp Score
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CTI Interest Score
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7.4$0-$5k0.72-

Summaryinfo

A vulnerability was found in filesystem_spec up to 2026.5.x. It has been rated as critical. The impacted element is the function _process_references1._render_jinja/_process_templates/_process_gen of the file fsspec/implementations/reference.py of the component ReferenceFileSystem. The manipulation leads to special elements in template engine. This vulnerability is traded as CVE-2026-104851. It is possible to initiate the attack remotely. There is no exploit available. Upgrading the affected component is advised.

Detailsinfo

A vulnerability was found in filesystem_spec up to 2026.5.x. It has been rated as critical. This issue affects the function _process_references1._render_jinja/_process_templates/_process_gen of the file fsspec/implementations/reference.py of the component ReferenceFileSystem. The manipulation with an unknown input leads to a special elements in template engine vulnerability. Using CWE to declare the problem leads to CWE-1336. The product uses a template engine to insert or process externally-influenced input, but it does not neutralize or incorrectly neutralizes special elements or syntax that can be interpreted as template expressions or other code directives when processed by the engine. Impacted is confidentiality, integrity, and availability. The summary by CVE is:

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.

The advisory is shared at github.com. The identification of this vulnerability is CVE-2026-104851 since 10/02/2026. The exploitation is known to be easy. The attack may be initiated remotely. No form of authentication is needed for a successful exploitation. It demands that the victim is doing some kind of user interaction. Technical details are known, but no exploit is available. MITRE ATT&CK project uses the attack technique T1221 for this issue.

Upgrading to version 2026.6.0 eliminates this vulnerability.

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Productinfo

Name

Version

CPE 2.3info

CPE 2.2info

CVSSv4info

VulDB Vector: 🔒
VulDB Reliability: 🔍

CVSSv3info

VulDB Meta Base Score: 7.6
VulDB Meta Temp Score: 7.4

VulDB Base Score: 6.3
VulDB Temp Score: 6.0
VulDB Vector: 🔒
VulDB Reliability: 🔍

CNA Base Score: 8.8
CNA Vector (GitHub_M): 🔒

CVSSv2info

AVACAuCIA
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VectorComplexityAuthenticationConfidentialityIntegrityAvailability
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VulDB Base Score: 🔒
VulDB Temp Score: 🔒
VulDB Reliability: 🔍

Exploitinginfo

Class: Special elements in template engine
CWE: CWE-1336 / CWE-791 / CWE-790
CAPEC: 🔒
ATT&CK: 🔒

Physical: No
Local: No
Remote: Yes

Availability: 🔒
Status: Not defined
Price Prediction: 🔍
Current Price Estimation: 🔒

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Threat Intelligenceinfo

Interest: 🔍
Active Actors: 🔍
Active APT Groups: 🔍

Countermeasuresinfo

Recommended: Upgrade
Status: 🔍

0-Day Time: 🔒

Upgrade: filesystem_spec 2026.6.0

Timelineinfo

10/02/2026 Advisory disclosed
10/02/2026 +0 days CVE reserved
10/02/2026 +0 days VulDB entry created
10/02/2026 +0 days VulDB entry last update

Sourcesinfo

Advisory: github.com
Status: Confirmed

CVE: CVE-2026-104851 (🔒)
GCVE (CVE): GCVE-0-2026-104851
GCVE (VulDB): GCVE-100-413189

Entryinfo

Created: 10/02/2026 18:54
Changes: 10/02/2026 18:54 (65)
Complete: 🔍
Cache ID: 216::103

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