{"id":"PYSEC-2026-3670","summary":"JupyterLab: PyPI extension blocklist package-name canonicalization bypass","details":"JupyterLab's PyPI extension manager enforces `blocked_extensions_uris` by comparing the requested install name to blocklist entries with a custom string normalization that is weaker than PyPI package-name canonicalization. An authenticated user can request a PyPI-equivalent spelling such as `JupyterLab.Git` for a blocklisted package such as `jupyterlab-git`; JupyterLab accepts the install request even though pip resolves the variant to the same package.\n\nThis has security implications only for deployments that combine all of the following:\n- an allowlist/blocklist configured with the intent of restricting which packages users can install;\n- the (default) PyPI Extension Manager enabled; and\n- kernels and terminals disabled or delegated to remote hosts (otherwise a user with kernel access can install packages directly regardless of this check) \n\n### Impact\n\nThe vulnerability lets an authenticated user install a package the operator specifically intended to block, defeating the allowlist/blocklist control. Because extensions in principle allow for arbitrary code execution, this vulnerability enables untrusted users to impact the integrity and availability of the jupyter-server instance that was provisioned to them. The user already has access to their own single-user server's data, so installing an extension grants no new read access.\n\nIn particular, the integrity of data can be impacted, and any hardening or restrictions on permitted user actions (download/upload limits) within the single-user server can be circumvented. Availability impact on a JupyterHub deployment is limited: while a user can be expected to exhaust their own kernel pod's resources, this vulnerability makes it easier to also exhaust the single-user server resources or generate more requests to shared resources; where limits are absent, resource exhaustion could potentially degrade the wider deployment.\n\n### Patches\n\nJupyterLab [`v4.6.2`](https://github.com/jupyterlab/jupyterlab/releases/tag/v4.6.2) and [`v4.5.10`](https://github.com/jupyterlab/jupyterlab/releases/tag/v4.5.10) contain the patch.\n\nUsers of applications that depend on JupyterLab, such as Notebook v7+, should update `jupyterlab` package too.\n\n### Workarounds\n\nNo action is required for deployments that do not have a custom allow/block list configured. Deployments wanting to disable programmatic extension installation entirely can switch to the read-only extension manager:\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\u003cimg width=\"293\" height=\"293\" alt=\"image\" src=\"https://github.com/user-attachments/assets/8016c809-633e-4ed0-a5bc-6bc4793caa0f\" /\u003e","aliases":["BIT-jupyterlab-2026-73416","CVE-2026-73416","GHSA-89vp-jrxv-24w8"],"modified":"2026-08-19T12:55:56.163961998Z","published":"2026-08-19T11:56:25.283562Z","references":[{"type":"WEB","url":"https://github.com/jupyterlab/jupyterlab/security/advisories/GHSA-89vp-jrxv-24w8"},{"type":"WEB","url":"https://github.com/jupyterlab/jupyterlab/pull/19184"},{"type":"WEB","url":"https://github.com/jupyterlab/jupyterlab/pull/19185"},{"type":"WEB","url":"https://github.com/jupyterlab/jupyterlab/pull/19186"},{"type":"WEB","url":"https://github.com/jupyterlab/jupyterlab/commit/be9303f5bcd5308eaeae953c5a3c903046682c2c"},{"type":"WEB","url":"https://github.com/jupyterlab/jupyterlab/commit/f1beab4a2027af4719d6edc07d52d6cf5a39a432"},{"type":"PACKAGE","url":"https://github.com/jupyterlab/jupyterlab"},{"type":"WEB","url":"https://github.com/jupyterlab/jupyterlab/releases/tag/v4.5.10"},{"type":"WEB","url":"https://github.com/jupyterlab/jupyterlab/releases/tag/v4.6.2"},{"type":"PACKAGE","url":"https://pypi.org/project/jupyterlab"},{"type":"ADVISORY","url":"https://github.com/advisories/GHSA-89vp-jrxv-24w8"},{"type":"ADVISORY","url":"https://nvd.nist.gov/vuln/detail/CVE-2026-73416"}],"affected":[{"package":{"name":"jupyterlab","ecosystem":"PyPI","purl":"pkg:pypi/jupyterlab"},"ranges":[{"type":"ECOSYSTEM","events":[{"introduced":"4.5.0"},{"fixed":"4.5.10"},{"introduced":"4.6.0"},{"fixed":"4.6.2"}]}],"versions":["4.5.0","4.5.1","4.5.2","4.5.3","4.5.4","4.5.5","4.5.6","4.5.7","4.5.8","4.5.9","4.6.0","4.6.1"],"database_specific":{"source":"https://github.com/pypa/advisory-database/blob/main/vulns/jupyterlab/PYSEC-2026-3670.yaml"}}],"schema_version":"1.9.0","severity":[{"type":"CVSS_V4","score":"CVSS:4.0/AV:N/AC:L/AT:P/PR:L/UI:N/VC:L/VI:H/VA:L/SC:N/SI:N/SA:N"}]}