fsspec — security advisory
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.
- Products
- fsspec
- Affected versions
- 0.6.1-0.1, 0.8.4-1, 2022.01.0-1, 2023.10.0-1, 2023.6.0-1, 2023.9.2-1, 2024.2.0-1, 2025.12.0-1, 2025.3.2-1ubuntu1
- Fixed versions
- Not specified
- CVEs
- CVE-2026-104851
- Confirmed fixed CVEs
- Not specified
- Updated in this feed
- 31 Oct 2026, 02:39 UTC · Revision 1
Source evidence
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.
osv:UBUNTU-CVE-2026-104851
fsspec
Fixed versions: Not specified
fsspec
Fixed versions: Not specified
fsspec
Fixed versions: Not specified
fsspec
Fixed versions: Not specified
fsspec
Fixed versions: Not specified
Complete source record
{
"id": "e2ea58ae926ee584c66dae48ec366c6d62fe678727a2a779745840429e3560b8",
"url": "https://osv.dev/vulnerability/UBUNTU-CVE-2026-104851",
"method": "structured",
"payload": {
"kind": "advisory",
"title": "UBUNTU-CVE-2026-104851",
"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.",
"evidence": "osv:UBUNTU-CVE-2026-104851",
"products": [
{
"name": {
"value": "fsspec",
"evidence": "/affected/0/package/name"
},
"prerequisites": [],
"fixed_versions": [],
"affected_versions": [
{
"value": "0.6.1-0.1",
"evidence": "/affected/0/versions"
}
]
},
{
"name": {
"value": "fsspec",
"evidence": "/affected/1/package/name"
},
"prerequisites": [],
"fixed_versions": [],
"affected_versions": [
{
"value": "0.8.4-1",
"evidence": "/affected/1/versions"
},
{
"value": "2022.01.0-1",
"evidence": "/affected/1/versions"
}
]
},
{
"name": {
"value": "fsspec",
"evidence": "/affected/2/package/name"
},
"prerequisites": [],
"fixed_versions": [],
"affected_versions": [
{
"value": "2023.6.0-1",
"evidence": "/affected/2/versions"
},
{
"value": "2023.9.2-1",
"evidence": "/affected/2/versions"
},
{
"value": "2023.10.0-1",
"evidence": "/affected/2/versions"
},
{
"value": "2024.2.0-1",
"evidence": "/affected/2/versions"
}
]
},
{
"name": {
"value": "fsspec",
"evidence": "/affected/3/package/name"
},
"prerequisites": [],
"fixed_versions": [],
"affected_versions": [
{
"value": "2025.12.0-1",
"evidence": "/affected/3/versions"
}
]
},
{
"name": {
"value": "fsspec",
"evidence": "/affected/4/package/name"
},
"prerequisites": [],
"fixed_versions": [],
"affected_versions": [
{
"value": "2025.3.2-1ubuntu1",
"evidence": "/affected/4/versions"
},
{
"value": "2025.12.0-1",
"evidence": "/affected/4/versions"
}
]
}
],
"severity": "high",
"structured": {
"id": "UBUNTU-CVE-2026-104851",
"aliases": [
"UBUNTU-CVE-2026-104851"
],
"metrics": [
{
"type": "CVSS_V3",
"score": "CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:H/I:H/A:H"
},
{
"type": "Ubuntu",
"score": "medium"
}
],
"affected": [
{
"ranges": [
{
"type": "ECOSYSTEM",
"events": [
{
"introduced": "0"
}
]
}
],
"package": {
"name": "fsspec",
"purl": "pkg:deb/ubuntu/fsspec?arch=source&distro=focal",
"ecosystem": "Ubuntu:20.04:LTS"
},
"versions": [
"0.6.1-0.1"
],
"database_specific": {
"source": "https://github.com/canonical/ubuntu-security-notices/blob/main/osv/cve/2026/UBUNTU-CVE-2026-104851.json"
},
"ecosystem_specific": {
"binaries": [
{
"binary_name": "python3-fsspec",
"binary_version": "0.6.1-0.1"
}
]
}
},
{
"ranges": [
{
"type": "ECOSYSTEM",
"events": [
{
"introduced": "0"
}
]
}
],
"package": {
"name": "fsspec",
"purl": "pkg:deb/ubuntu/fsspec?arch=source&distro=jammy",
"ecosystem": "Ubuntu:22.04:LTS"
},
"versions": [
"0.8.4-1",
"2022.01.0-1"
],
"database_specific": {
"source": "https://github.com/canonical/ubuntu-security-notices/blob/main/osv/cve/2026/UBUNTU-CVE-2026-104851.json"
},
"ecosystem_specific": {
"binaries": [
{
"binary_name": "python3-fsspec",
"binary_version": "2022.01.0-1"
}
]
}
},
{
"ranges": [
{
"type": "ECOSYSTEM",
"events": [
{
"introduced": "0"
}
]
}
],
"package": {
"name": "fsspec",
"purl": "pkg:deb/ubuntu/fsspec?arch=source&distro=noble",
"ecosystem": "Ubuntu:24.04:LTS"
},
"versions": [
"2023.6.0-1",
"2023.9.2-1",
"2023.10.0-1",
"2024.2.0-1"
],
"database_specific": {
"source": "https://github.com/canonical/ubuntu-security-notices/blob/main/osv/cve/2026/UBUNTU-CVE-2026-104851.json"
},
"ecosystem_specific": {
"binaries": [
{
"binary_name": "python3-fsspec",
"binary_version": "2024.2.0-1"
}
]
}
},
{
"ranges": [
{
"type": "ECOSYSTEM",
"events": [
{
"introduced": "0"
}
]
}
],
"package": {
"name": "fsspec",
"purl": "pkg:deb/ubuntu/fsspec?arch=source&distro=stonking",
"ecosystem": "Ubuntu:26.10"
},
"versions": [
"2025.12.0-1"
],
"database_specific": {
"source": "https://github.com/canonical/ubuntu-security-notices/blob/main/osv/cve/2026/UBUNTU-CVE-2026-104851.json"
},
"ecosystem_specific": {
"binaries": [
{
"binary_name": "python3-fsspec",
"binary_version": "2025.12.0-1"
}
]
}
},
{
"ranges": [
{
"type": "ECOSYSTEM",
"events": [
{
"introduced": "0"
}
]
}
],
"package": {
"name": "fsspec",
"purl": "pkg:deb/ubuntu/fsspec?arch=source&distro=resolute",
"ecosystem": "Ubuntu:26.04:LTS"
},
"versions": [
"2025.3.2-1ubuntu1",
"2025.12.0-1"
],
"database_specific": {
"source": "https://github.com/canonical/ubuntu-security-notices/blob/main/osv/cve/2026/UBUNTU-CVE-2026-104851.json"
},
"ecosystem_specific": {
"binaries": [
{
"binary_name": "python3-fsspec",
"binary_version": "2025.12.0-1"
}
]
}
}
],
"modified": "2026-10-17T12:58:42.713511223Z",
"provider": "osv",
"upstream": [
"CVE-2026-104851"
],
"references": [
"https://ubuntu.com/security/CVE-2026-104851",
"https://www.cve.org/CVERecord?id=CVE-2026-104851",
"https://github.com/fsspec/filesystem_spec/security/advisories/GHSA-27vj-qcqg-25rc",
"https://github.com/fsspec/filesystem_spec/commit/86438783f93b1398ef245b92f0e6063b445b611c",
"https://github.com/fsspec/filesystem_spec/commit/a1c16ab3f07f354aa371c38f7b1b07ea7fd4c5c8",
"https://github.com/fsspec/filesystem_spec/pull/2029",
"https://github.com/fsspec/filesystem_spec/pull/2039",
"https://github.com/fsspec/filesystem_spec/releases/tag/2026.6.0"
]
},
"related_cves": [
{
"value": "CVE-2026-104851",
"evidence": "/upstream"
}
],
"security_relevant": true,
"severity_evidence": "/severity/0/score"
},
"source_id": "core-osv",
"document_id": 358978,
"published_at": "2026-10-02T17:17:00+00:00"
}