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🛡️ CVE-2026-42266 — jupyterlab

🟠 CVSS 8.0 — High ✅ No Known Exploit CWE-20 OSV
8.0
CVSS Score
0 Low4 Medium7 High9 Critical10

Description

JupyterLab has an Extension Manager API/GUI Policy Discrepancy, allowing 3rd party (malicious) extensions install via POST request

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.

This has security implications for deployments that:

  • have allow-listed specific extensions with aim to prevent users from installing packages
  • have the kernel and terminals disabled or delegated to remote hosts (thus no access to install packages in the single-user server environment)
  • 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)
  • have the (default) PyPI Extension Manager enabled

Impact

An 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.

Patches

JupyterLab [v4.5.7](https://github.com/jupyterlab/jupyterlab/releases/tag/v4.5.7) contains the patch.

Users of applications that depend on JupyterLab, such as Notebook v7+, should update jupyterlab package too.

Workarounds

Switch to read-only extension manager by adding the following command line option:

```bash

--LabApp.extension_manager=readonly

```

or the following traitlet:

```python

c.LabApp.extension_manager = 'readonly'

```

You can confirm that the read-only manager is in use from GUI:

<img width="293" height="293" alt="image" src="https://github.com/user-attachments/assets/8016c809-633e-4ed0-a5bc-6bc4793caa0f" />

Note: configuration of a PyPI proxy with allow-listed packages is not sufficient to protect from this vulnerability.

References

  • allow-list https://jupyterlab.readthedocs.io/en/stable/user/extensions.html#listing-configuration
  • https://jupyterhub.readthedocs.io/en/5.2.1/explanation/websecurity.html
  • https://jupyterlab.readthedocs.io/en/latest/user/extensions.html#extension-manager-implementations

How this vulnerability can be exploited

This issue can be reached over the network, attack complexity is low, an attacker needs low-level privileges on the target. No user interaction is required. The scope is unchanged, so the impact stays within the vulnerable component. Rated impact: confidentiality high, integrity high, availability high.

CVSS metrics in full

The score comes from this vector: CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H

  • Attack vector: Network — reachable from anywhere that can route to the service.
  • Attack complexity: Low — the attack works reliably, with no preparation.
  • Privileges required: Low — an ordinary user account is enough.
  • User interaction: None — nobody has to be tricked into anything.
  • Scope: Unchanged — the damage stays inside the vulnerable component.
  • Confidentiality impact: High — total loss, or loss the attacker controls.
  • Integrity impact: High — total loss, or loss the attacker controls.
  • Availability impact: High — total loss, or loss the attacker controls.

Weakness class

CVE-2026-42266 is classified as CWE-20: Improper Input Validation. The application accepts input without checking that it has the expected form, so malformed values reach code that assumes they are well formed.

Affected software

CVE-2026-42266 is recorded against 1 package.

  • jupyterlab (from 4.0.0 up to 4.5.7)

Timeline and source

Published on 5 May 2026 and last revised on 27 July 2026. No public exploit is currently recorded for this entry. A vendor advisory or fix has been published. Record sourced from OSV.

References

github.com (Web)
nvd.nist.gov (Advisory)
github.com (Package)
github.com (Web)
github.com (Web)
jupyterhub.readthedocs.io (Web)
jupyterlab.readthedocs.io (Web)

Other advisories for this package

jupyterlab has other advisories on record. If you are patching this one, these are worth checking on the same host:

Same weakness in other software

These advisories are the same class of weakness (CWE-20: Improper Input Validation) in other software:

CVE-2026-42266 on other distributions

Each distribution ships its own build and its own fixed version. Pick the one you run:

Details

Severity HIGH
CVSS Score 8.0
CVSS Vector CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H
CWE CWE-20
Public Exploit ✅ No
Source OSV
Published 2026-05-05
Updated 2026-08-20
Modified 2026-07-27

Affected Packages

Software From version Fixed in
jupyterlab 4.0.0 4.5.7

Site Security Check

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ⓘ Data Notice: The information presented above has been compiled from publicly available internet sources. Boteraser aggregates this data solely for informational purposes and does not independently classify, evaluate, or endorse any findings about the vulnerabilities listed. The accuracy and completeness of this information is the sole responsibility of the original publishers. Boteraser and its operators accept no liability for any decisions made based on this data.

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