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Fencer Intel
high 8.8

CVE-2026-104851 json

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

published last mo. modified 25d ago also GHSA-27vj-qcqg-25rc , PYSEC-2026-4217 , EUVD-2026-91720

cvss
8.8
version 3.1, CNA
cisa kev
Not listed
not in CISA's catalog
epss
0.5%
EPSS 0.5% chance of exploitation in 30 days, percentile 41%
public exploits
0
none known

Summary

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.

Patch / fix

  • pypi fsspec 2026.6.0
  • fsspec Debian 14 2026.9.0-1

debian advisories DEBIAN-CVE-2026-104851

  • python-fsspec openSUSE Leap 16.0 2024.3.1-bp160.2.1

opensuse advisories openSUSE-SU-2026:22028-1

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Vendor advisories

What the vendors themselves say about their products: affected, fixed or not affected, and what to do.

red hat product security vex CVE-2026-104851 updated cvss 8.8

fsspec: fsspec: arbitrary code execution via unrestricted template rendering in ReferenceFileSystem

  • Red Hat Exploit Intelligence exploit-intelligence/vulnerability-analysis-rhel9 Red Hat Lightspeed Core lightspeed-core/rag-tool-cpu-rhel9, lightspeed-core/lightspeed-stack-rhel9, lightspeed-core/rag-tool-cuda-12.9-rhel9 Red Hat OpenShift Lightspeed openshift-lightspeed/lightspeed-ocp-rag-rhel9, openshift-lightspeed/lightspeed-service-api-rhel9, openshift-lightspeed-tech-preview/lightspeed-rag-tool-rhel9
    affected: workaround, no fix available
  • Red Hat AI Inference Server rhaii/vllm-tpu-rhel9, rhaiis/vllm-cpu-rhel9, rhaiis/vllm-tpu-rhel9, rhaii/vllm-gaudi-rhel9, rhaiis/vllm-cuda-rhel9, rhaiis/vllm-rocm-rhel9, +4 more
    affected: workaround, no fix available, no fix planned “Will not fix”
  • Red Hat Enterprise Linux AI (RHEL AI) 3 rhelai3/bootc-gaudi-rhel9
    affected: workaround, no fix planned “Will not fix”
  • Red Hat OpenShift AI (RHOAI) rhoai/odh-ogx-core-rhel9, rhoai/odh-vllm-gaudi-rhel9, rhoai/odh-llm-d-kv-cache-rhel9, rhoai/odh-llama-stack-core-rhel9, rhoai/odh-caikit-tgis-serving-rhel9, rhoai/odh-th06-cpu-torch210-py312-rhel9, +8 more
    affected: workaround, no fix available, no fix planned “Will not fix”
  • Red Hat Satellite 6 satellite/iop-insights-engine-rhel9
    affected: workaround, no fix available
  • Red Hat AI Inference Server 3.4 rhaii/vllm-cpu-rhel9 1791857301, rhaii/vllm-cuda-rhel9 1791857183, rhaii/vllm-rocm-rhel9 1791856725, rhaii/vllm-spyre-rhel9 1791858592, rhaii/model-opt-cuda-rhel9 1791857110
    fixed: vendor fix RHSA-2026:83116
  • Red Hat AI Inference Server 3.5 rhaii/vllm-spyre-rhel9 1791818357
    fixed: vendor fix RHSA-2026:82371
  • Red Hat Ansible Automation Platform 2.6 ansible-automation-platform-26/lightspeed-chatbot-rhel9 1791978798
    fixed: vendor fix RHSA-2026:87120
show 6 more
  • Red Hat Ansible Automation Platform 2.7 ansible-automation-platform-27/lightspeed-chatbot-rhel9 1792385971
    fixed: vendor fix RHSA-2026:87124
  • Red Hat Enterprise Linux AI 3.4 rhelai3/bootc-cuda-rhel9 1792612985, rhelai3/bootc-rocm-rhel9 1792612921, rhelai3/bootc-aws-cuda-rhel9 1792680701, rhelai3/bootc-gcp-cuda-rhel9 1792680694, rhelai3/disk-image-cuda-rhel9 1792701796, rhelai3/bootc-azure-cuda-rhel9 1792680694, +1 more
    fixed: vendor fix RHSA-2026:90440
  • Red Hat OpenShift AI 2.25 rhoai/odh-caikit-nlp-rhel9 1791448212, rhoai/odh-feature-server-rhel9 1792148523
    fixed: vendor fix RHSA-2026:87410
  • Red Hat OpenShift AI 3.4 rhoai/odh-automl-rhel9 1791535789, rhoai/odh-mlflow-rhel9 1791865967, rhoai/odh-autorag-rhel9 1791557539, rhoai/odh-ta-lmes-job-rhel9 1791470318, rhoai/odh-kserve-agent-rhel9 1791468381, rhoai/odh-kserve-router-rhel9 1791468401, +21 more
    fixed: vendor fix RHSA-2026:84734
  • Red Hat OpenShift AI 3.5 rhai/guidellm-rhel9 1793719302, rhoai/odh-mlflow-rhel9 1791947857, rhoai/odh-ta-lmes-job-rhel9 1792501995, rhoai/odh-th-torch-cpu-py312-rhel9 1791926611, rhoai/odh-th-torch-cuda-py312-rhel9 1791927642, rhoai/odh-th-torch-rocm-py312-rhel9 1791925861, +22 more
    fixed: vendor fix RHSA-2026:94631
  • Red Hat Ansible Automation Platform 2 ansible-automation-platform-25/lightspeed-chatbot-rhel8 Red Hat Ansible Automation Platform 2.6 ansible-automation-platform-26/hub-rhel9 1791947385, ansible-automation-platform-26/gateway-rhel9 1791971533, ansible-automation-platform-26/hub-web-rhel9 1791952205, ansible-automation-platform-26/receptor-rhel9 1791968536, ansible-automation-platform-26/mcp-tools-rhel9 1791941340, ansible-automation-platform-26/controller-rhel9 1791947602, +24 more Red Hat Ansible Automation Platform 2.7 ansible-automation-platform-27/hub-rhel9 1792388670, ansible-automation-platform-27/gateway-rhel9 1792429216, ansible-automation-platform-27/hub-web-rhel9 1792394496, ansible-automation-platform-27/receptor-rhel9 1792139928, ansible-automation-platform-27/mcp-tools-rhel9 1792425046, ansible-automation-platform-27/controller-rhel9 1792389457, +26 more Red Hat OpenShift AI (RHOAI) rhoai/odh-built-in-detector-rhel9, rhoai/odh-th06-cpu-torch291-py312-rhel9, rhoai/odh-llm-d-inference-scheduler-rhel9, rhoai/odh-th06-cuda130-torch291-py312-rhel9 Red Hat OpenShift AI 2.25 rhoai/odh-rhel9-operator 1792570619, rhoai/odh-vllm-cpu-rhel9 1792018436, rhoai/odh-dashboard-rhel9 1791853525, rhoai/odh-modelmesh-rhel9 1790881700, rhoai/odh-operator-bundle 1792571069, rhoai/odh-vllm-cuda-rhel9 1791358976, +64 more Red Hat OpenShift AI 3.4 rhoai/odh-cli-rhel9 1791509689, rhoai/odh-cli-rhel9 1792722177, rhoai/rhai-cli-rhel9 1791509689, rhoai/rhai-cli-rhel9 1792722177, rhoai/odh-automl-rhel9 1792697253, rhoai/odh-mlflow-rhel9 1793002327, +179 more
    +1 more products
    Red Hat OpenShift AI 3.5 rhoai/odh-cli-rhel9 1791945905, rhoai/rhai-cli-rhel9 1791945905, rhoai/odh-automl-rhel9 1791916705, rhoai/odh-autorag-rhel9 1791903266, rhoai/odh-trainer-rhel9 1791952138, rhoai/odh-core-bff-rhel9 1791945789, +86 more
    not affected: vulnerable code not present

Red Hat CSAF VEX © Red Hat, Inc., from https://security.access.redhat.com/data/csaf/v2/vex/; changed: reduced to product statuses and remediations. CC BY 4.0 · csaf

CISA SSVC

Exploitation
Proof of concept is public
Automatable
no
Technical impact
total
Assessed
last mo.

Exploit prediction

0.48% chance of exploitation in the next 30 days, higher than 41% of all scored CVEs (FIRST EPSS, 2026-11-09).

Exploits and checks

  • github.com https://github.com/fsspec/filesystem_spec/security/advisories/GHSA-27vj-qcqg-25rc referenced PoC, tagged "exploit" by a source, unverified

CVSS scores

assigned by version score vector
CNA 3.1 8.8 CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:H/I:H/A:H
GitHub 3.1 8.8 CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:H/I:H/A:H
OSV 3.1 8.8 CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:H/I:H/A:H

Affected packages

ecosystem package affected fixed in
pypi fsspec
>=0.9.0, <2026.6.0
2026.6.0

Affected products

  • fsspec filesystem_spec

Classification

Weakness
  • CWE-94 Improper Control of Generation of Code
  • CWE-1336 Improper Neutralization of Special Elements Used in a Template Engine

References

Sources

Fencer Intel keeps one entry per vulnerability: the CVE id wins, then GHSA, and records that alias each other are merged, except that two CVEs always keep separate entries. The same data is available as JSON.