Vulnerability · Published Oct 2, 2026 · Assigned by GitHub_M
CVE-2026-104851fsspec: Server-Side Template Injection in ReferenceFileSystem leads to Remote Code Execution
High 8.8
In plain English
A high-severity code injection in filesystem_spec from fsspec. Proof-of-concept exploit code is public. The chance it is exploited in the next 30 days is estimated at 0.5% (higher than 41% of all known vulnerabilities). Fixed versions are available - upgrade the affected package.
Official 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.
Affected packages & fixed versions
| Ecosystem | Package | Fixed in | Advisory |
|---|---|---|---|
| Debian:12 | fsspec | no fix listed | DEBIAN-CVE-2026-104851 |
| Debian:13 | fsspec | no fix listed | DEBIAN-CVE-2026-104851 |
| Debian:14 | fsspec | 2026.9.0-1 | DEBIAN-CVE-2026-104851 |
| PyPI | fsspec | 2026.6.0 | GHSA-27vj-qcqg-25rc |
| PyPI | fsspec | 2026.6.0 | PYSEC-2026-4217 |
| Ubuntu:22.04:LTS | fsspec | no fix listed | UBUNTU-CVE-2026-104851 |
| Ubuntu:24.04:LTS | fsspec | no fix listed | UBUNTU-CVE-2026-104851 |
| Ubuntu:26.04:LTS | fsspec | no fix listed | UBUNTU-CVE-2026-104851 |
| Ubuntu:26.10 | fsspec | no fix listed | UBUNTU-CVE-2026-104851 |
Affected products (as reported)
| Vendor | Product | Versions |
|---|---|---|
| fsspec | filesystem_spec | >= 0.9.0, < 2026.6.0 |
Weakness: CWE-94, CWE-1336 · Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:H/I:H/A:H
References
- https://github.com/fsspec/filesystem_spec/security/advisories/GHSA-27vj-qcqg-25rc x_refsource_CONFIRM
- https://github.com/fsspec/filesystem_spec/pull/2029 x_refsource_MISC
- https://github.com/fsspec/filesystem_spec/pull/2039 x_refsource_MISC
- https://github.com/fsspec/filesystem_spec/commit/86438783f93b1398ef245b92f0e6063b445b611c x_refsource_MISC
- https://github.com/fsspec/filesystem_spec/commit/a1c16ab3f07f354aa371c38f7b1b07ea7fd4c5c8 x_refsource_MISC
- https://github.com/fsspec/filesystem_spec/releases/tag/2026.6.0 x_refsource_MISC