CVE-2026-35397: Jupyter Server Path Traversal Vulnerability

{
  "schema_version" : "1.4.0",
  "id" : "GHSA-5789-5fc7-67v3",
  "modified" : "2026-08-28T18:30:43Z",
  "published" : "2026-05-05T16:49:10Z",
  "aliases" : [ "CVE-2026-35397" ],
  "summary" : "Jupyter Server: Path Traversal via incorrect startswith() root directory check allows access to sibling directories",
  "details" : "### Summary\n\nJupyter Server <=2.17.0 can access directories sibling to the root directory, if it starts with the root dir's name.\n\n### PoC\n\nMinimal:\n\n```\n.\n├── test/              <- root directory.\n│   └── test.txt\n└── testtest/\n    └── secret.txt     <- 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'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.\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.",
  "severity" : [ {
    "type" : "CVSS_V3",
    "score" : "CVSS:3.1/AV:N/AC:H/PR:L/UI:N/S:U/C:H/I:H/A:L"
  }, {
    "type" : "CVSS_V4",
    "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"
  } ],
  "affected" : [ {
    "package" : {
      "ecosystem" : "PyPI",
      "name" : "jupyter-server"
    },
    "ranges" : [ {
      "type" : "ECOSYSTEM",
      "events" : [ {
        "introduced" : "0"
      }, {
        "fixed" : "2.18.0"
      } ]
    } ],
    "database_specific" : {
      "last_known_affected_version_range" : "<= 2.17.0"
    }
  } ],
  "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"
  } ],
  "database_specific" : {
    "cwe_ids" : [ "CWE-22" ],
    "severity" : "HIGH",
    "github_reviewed" : true,
    "github_reviewed_at" : "2026-05-05T16:49:10Z",
    "nvd_published_at" : "2026-05-05T20:16:38Z"
  }
}