JupyterLab CVE-2026-42266: PyPI Extension Manager Bypass
The National Vulnerability Database has disclosed CVE-2026-42266, a high-severity vulnerability (CVSS 8.8) affecting JupyterLab versions 4.0.0 through 4.5.6. This flaw allows the PyPI Extension Manager to bypass its intended allow-list (allowed_extensions_uris), enabling the installation of extensions from sources beyond the default PyPI index.
This isn’t just a misconfiguration; it’s a critical breakdown in trust boundaries. JupyterLab’s extensibility is a core feature, but when the gatekeeper for those extensions fails, it opens a direct channel for malicious code execution. An attacker with even low-privileged access to a JupyterLab instance could leverage this to install arbitrary, unvetted packages, leading to full compromise of the underlying system. The attacker’s calculus here is straightforward: exploit the trusted extension mechanism to achieve persistent access or escalate privileges.
Defenders need to recognize the severe implications. This isn’t theoretical; it’s a clear path to RCE. The fix is in JupyterLab version 4.5.7. Organizations using affected versions must prioritize this patch. This is a supply chain risk within your own tools, enabling insiders or compromised accounts to introduce further risk.
What This Means For You
- If your organization uses JupyterLab, check your deployment's version immediately. Any instance running 4.0.0 through 4.5.6 is vulnerable to unauthorized extension installation. Patch to version 4.5.7 without delay. Audit your JupyterLab environments for any unexpected or unapproved extensions.
Related ATT&CK Techniques
🛡️ Detection Rules
3 rules · 6 SIEM formats3 detection rules auto-generated for this incident, mapped to MITRE ATT&CK. Sigma YAML is free — export to any SIEM format via the Intel Bot.
JupyterLab PyPI Extension Manager Bypass Attempt (CVE-2026-42266) - Free Tier
title: JupyterLab PyPI Extension Manager Bypass Attempt (CVE-2026-42266) - Free Tier
id: scw-2026-05-13-ai-1
status: experimental
level: high
description: |
Detects attempts to install JupyterLab extensions from PyPI using the extension manager, which is vulnerable in versions 4.0.0 to 4.5.6. This rule specifically looks for the 'jupyter-server' process executing an 'install' command that references PyPI URLs, indicating a potential exploitation of CVE-2026-42266 where the allow-list of extensions was not properly enforced.
author: SCW Feed Engine (AI-generated)
date: 2026-05-13
references:
- https://shimiscyberworld.com/posts/nvd-CVE-2026-42266/
tags:
- attack.initial_access
- attack.t1190
logsource:
category: process_creation
detection:
selection:
Image|endswith:
- 'jupyter-server'
CommandLine|contains:
- 'install'
- '--pyproject'
CommandLine|contains_any:
- 'pypi.org'
- 'files.pythonhosted.org'
condition: selection
falsepositives:
- Legitimate administrative activity
Source: Shimi's Cyber World · License & reuse
Indicators of Compromise
| ID | Type | Indicator |
|---|---|---|
| CVE-2026-42266 | Misconfiguration | jupyterlab versions 4.0.0 to 4.5.6 |
| CVE-2026-42266 | Misconfiguration | JupyterLab PyPI Extension Manager allow-list bypass (allowed_extensions_uris) |
Written by SCW Vulnerability Desk
Source & Attribution
| Source Platform | NVD |
| Channel | National Vulnerability Database |
| Published | May 13, 2026 at 19:16 UTC |
This content was AI-rewritten and enriched by Shimi's Cyber World based on the original source. All intellectual property rights remain with the original author.
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