CVE-2026-42266: Jupyterlab JupyterLab Has An Extension Manager Vulnerability

{
  "schema_version" : "1.4.0",
  "id" : "GHSA-37w4-hwhx-4rc4",
  "modified" : "2026-06-08T20:15:06Z",
  "published" : "2026-05-05T20:53:18Z",
  "aliases" : [ "CVE-2026-42266" ],
  "summary" : "JupyterLab has an Extension Manager API/GUI Policy Discrepancy, allowing 3rd party (malicious) extensions install via POST request",
  "details" : "The allow-list of extensions that can be installed from PyPI Extension Manager (`allowed_extensions_uris`) is not correctly enforced by JupyterLab prior to 4.5.7. The PyPI Extension Manager was not contained to packages listed on the default PyPI index.\n\nThis has security implications for deployments that:\n- have allow-listed specific extensions with aim to prevent users from installing packages\n- have the kernel and terminals disabled or delegated to remote hosts (thus no access to install packages in the single-user server environment)\n- have multi-tenant deployments that is not configured for untrusted users (as per documented on JupyterHub https://jupyterhub.readthedocs.io/en/5.2.1/explanation/websecurity.html)\n- have the (default) PyPI Extension Manager enabled\n\n### Impact\n\nAn authenticated attacker - such as a student in a shared JupyterHub environment or a user in a multi-tenant JupyterLab deployment - can escalate their privileges. This might allow for data exfiltration, lateral movement within the network, and persistent compromise of the server infrastructure.\n\n### Patches\n\nJupyterLab [`v4.5.7`](https://github.com/jupyterlab/jupyterlab/releases/tag/v4.5.7) contains the patch.\n\nUsers of applications that depend on JupyterLab, such as Notebook v7+, should update `jupyterlab` package too.\n\n### Workarounds\n\nSwitch to read-only extension manager by adding the following command line option:\n\n```bash\n--LabApp.extension_manager=readonly\n```\n\nor the following traitlet:\n\n```python\nc.LabApp.extension_manager = 'readonly'\n```\n\nYou can confirm that the read-only manager is in use from GUI:\n\n<img width=\"293\" height=\"293\" alt=\"image\" src=\"https://github.com/user-attachments/assets/8016c809-633e-4ed0-a5bc-6bc4793caa0f\" />\n\nNote: configuration of a PyPI proxy with allow-listed packages is not sufficient to protect from this vulnerability.\n\n### References\n\n- allow-list https://jupyterlab.readthedocs.io/en/stable/user/extensions.html#listing-configuration\n- https://jupyterhub.readthedocs.io/en/5.2.1/explanation/websecurity.html\n- https://jupyterlab.readthedocs.io/en/latest/user/extensions.html#extension-manager-implementations",
  "severity" : [ {
    "type" : "CVSS_V3",
    "score" : "CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H"
  } ],
  "affected" : [ {
    "package" : {
      "ecosystem" : "PyPI",
      "name" : "jupyterlab"
    },
    "ranges" : [ {
      "type" : "ECOSYSTEM",
      "events" : [ {
        "introduced" : "4.0.0"
      }, {
        "fixed" : "4.5.7"
      } ]
    } ],
    "database_specific" : {
      "last_known_affected_version_range" : "<= 4.5.6"
    }
  } ],
  "references" : [ {
    "type" : "WEB",
    "url" : "https://github.com/jupyterlab/jupyterlab/security/advisories/GHSA-37w4-hwhx-4rc4"
  }, {
    "type" : "ADVISORY",
    "url" : "https://nvd.nist.gov/vuln/detail/CVE-2026-42266"
  }, {
    "type" : "PACKAGE",
    "url" : "https://github.com/jupyterlab/jupyterlab"
  }, {
    "type" : "WEB",
    "url" : "https://github.com/jupyterlab/jupyterlab/releases/tag/v4.5.7"
  }, {
    "type" : "WEB",
    "url" : "https://github.com/pypa/advisory-database/tree/main/vulns/jupyterlab/PYSEC-2026-164.yaml"
  }, {
    "type" : "WEB",
    "url" : "https://jupyterhub.readthedocs.io/en/5.2.1/explanation/websecurity.html"
  }, {
    "type" : "WEB",
    "url" : "https://jupyterlab.readthedocs.io/en/latest/user/extensions.html#extension-manager-implementations"
  } ],
  "database_specific" : {
    "cwe_ids" : [ "CWE-20", "CWE-602", "CWE-88" ],
    "severity" : "HIGH",
    "github_reviewed" : true,
    "github_reviewed_at" : "2026-05-05T20:53:18Z",
    "nvd_published_at" : "2026-05-13T16:16:47Z"
  }
}