vulnerability / NVI-00013009 / Revision 2
fsspec: Server-Side Template Injection in ReferenceFileSystem leads to Remote Code Execution
GitHub lists this reviewed advisory for fsspec. Published version ranges and source prerequisites are shown below; this is not an inspection of a visitor’s application.
This report has not inspected your inventory, configuration, deployed build, reachability or evidence. A catalog listing and a severity score do not establish exposure or compromise.
01 / Meaning
Why it matters
Published affected context helps an owner decide what evidence to gather. This report has not examined your application.
8.8 high
GitHub source severity; exploitability and local consequence require separate evidence.
As of · GitHub Advisory Database
8.8 HIGH (3.1)
security-advisories@github.com severity; no combined Null risk score.
02 / Applicability
The affected context
Affected versions, configuration prerequisites and known exclusions are public. Confirm each one against the deployed service.
fsspec
source listed>= 0.9.0, < 2026.6.0
### Summary `fsspec.implementations.reference.ReferenceFileSystem` parses a "references" JSON document (Kerchunk format) supplied either inline or via a URL. The parser renders fields from this JSON through **un-sandboxed** `jinja2.Template(...).render(...)` calls in three locations. An attacker who controls the JSON document — typically by hosting it at a URL that the victim opens with `fsspec.filesystem("reference", fo=URL)` or via `xarray.open_dataset("reference://...")` — achieves arbitrary Python code execution on the victim machine, before any data is read. This mirrors the pattern of CVE-2024-34359 in `llama-cpp-python`, where externally-sourced template strings were rendered with the default unrestricted Jinja2 environment. ### Affected versions All versions of `fsspec` from `0.9.0` onward (vulnerable code introduced in commit `0fb8d56b684ee74ad9ad4587fd560bde1b116450`, 2021-03-12). Confirmed on the latest released version `2025.10.0`. ### Affected sinks All in `fsspec/implementations/reference.py`: | Sink | Location | Trigger | |---|---|---| | A — `_process_references1._render_jinja` | lines 1016-1018 | `simple_temp
03 / Response
What to do next
- investigate
Identify the exact component and deployed version, examine the linked publisher’s conditions, and retain evidence of any mitigation.
Confirm current vendor support, compatibility and deployment evidence. This report has not tested a fix in your system. NIST National Vulnerability Database
A fixed release is not deployment evidence.
Check current vendor support and compatibility. After making a change, verify the deployed build and relevant runtime conditions. Keep the evidence, owner and time. An updated lockfile alone does not prove what is running.
04 / Limits
What this report cannot establish
- Customer inventory, deployment, reachability and exploitation have not been inspected.
- NVD lastModified does not establish freshness of every associated CPE record.
05 / Provenance
Sources you can inspect
Each assertion retains its source. Mirrored records may repeat one underlying publisher; additional links are not independent corroboration.
- GHSA-27vj-qcqg-25rc ↗
GitHub Advisory Database · vendor advisory
Observed . GitHub Advisory Database; CC-BY-4.0. Each advisory links its original attribution. Null normalizes fields.
- CVE-2026-104851 ↗
NIST National Vulnerability Database · official catalog
Observed . This product uses data from the NVD API but is not endorsed or certified by the NVD.
Public revision history
Only published revisions appear here. Routine fetches do not create a material-change event.
- Revision 2 ·
Source facts changed; compare the preserved prior revision.
- Revision 1 ·
First indexed by Null; source disclosure date is shown separately.