CVE-2026-42266: Extension Installation Vulnerability in JupyterLab
Platform
python
Component
jupyterlab
Fixed in
4.5.7
CVE-2026-42266 is a high-severity vulnerability affecting JupyterLab versions 4.0.0 through 4.5.6. It allows attackers to bypass the intended restriction on extension sources, enabling the installation of malicious extensions from outside the default PyPI index. This can lead to arbitrary code execution within the JupyterLab environment. The vulnerability is fixed in version 4.5.7 and has been published on May 13, 2026.
Detect this CVE in your project
Upload your requirements.txt file and we'll tell you instantly if you're affected.
Impact and Attack Scenarios
The core impact of CVE-2026-42266 lies in the ability to install arbitrary extensions. An attacker could leverage this to inject malicious code into the JupyterLab environment, gaining control over user sessions and potentially accessing sensitive data. This could manifest as a rogue extension that steals credentials, modifies notebooks, or even compromises the underlying system. The blast radius extends to any user utilizing a vulnerable JupyterLab instance, particularly those with administrative privileges or access to sensitive data within notebooks. While no direct precedent exists mirroring this exact vulnerability, the potential for malicious extension installation shares similarities with other supply chain attacks targeting software ecosystems.
Exploitation Context
CVE-2026-42266 is currently not listed on KEV (Kernel Exploit Vulnerability Database) or EPSS (Exploit Prediction Scoring System). The lack of an EPSS score suggests a low to medium probability of exploitation, primarily due to the technical expertise required to identify and exploit the vulnerability. No public proof-of-concept (POC) code has been publicly released as of the publication date. The NVD (National Vulnerability Database) and CISA (Cybersecurity and Infrastructure Security Agency) entries were published on May 13, 2026.
Threat Intelligence
Exploit Status
CISA SSVC
CVSS Vector
What do these metrics mean?
- Attack Vector
- Network — remotely exploitable over the internet. No physical or local access required. Widest attack surface.
- Attack Complexity
- Low — no special conditions required. Attacker can exploit reliably without depending on rare configurations or timing.
- Privileges Required
- Low — any valid user account is sufficient. Basic authenticated access required.
- User Interaction
- None — attack is automatic and silent. Victim does nothing: no click, no file open.
- Scope
- Unchanged — impact is limited to the vulnerable component itself.
- Confidentiality
- High — complete confidentiality loss. Attacker can read all data: credentials, keys, personal data.
- Integrity
- High — attacker can write, modify, or delete any data: databases, config files, or code.
- Availability
- High — complete crash or resource exhaustion. Full denial of service.
Affected Software
Weakness Classification (CWE)
Timeline
- Reserved
- Published
Mitigation and Workarounds
The primary mitigation for CVE-2026-42266 is to upgrade JupyterLab to version 4.5.7 or later. If upgrading is not immediately feasible, consider implementing stricter network controls to prevent JupyterLab instances from accessing untrusted PyPI mirrors. Additionally, review and audit existing JupyterLab extensions to identify any potentially malicious or outdated components. While a WAF or proxy cannot directly prevent this vulnerability, they can be configured to monitor for suspicious extension installation requests. There are no specific Sigma or YARA rules available for this vulnerability at this time, but monitoring extension installation logs is recommended.
How to fix
Actualice JupyterLab a la versión 4.5.7 o superior para mitigar esta vulnerabilidad. La actualización corrige la política de cumplimiento de la lista de control de acceso de las extensiones, evitando la instalación de extensiones maliciosas desde fuentes no autorizadas.
Frequently asked questions
What is CVE-2026-42266 — Extension Installation Vulnerability in JupyterLab?
CVE-2026-42266 is a high-severity vulnerability in JupyterLab (versions 4.0.0–<4.5.7) that allows attackers to bypass extension source restrictions and install malicious extensions from arbitrary PyPI sources, potentially leading to code execution.
Am I affected by CVE-2026-42266 in JupyterLab?
You are affected if you are using JupyterLab versions 4.0.0 through 4.5.6. Check your version using jupyter lab --version.
How do I fix CVE-2026-42266 in JupyterLab?
Upgrade JupyterLab to version 4.5.7 or later. This resolves the vulnerability by correctly enforcing the allowedextensionsuris list.
Is CVE-2026-42266 being actively exploited?
As of May 13, 2026, there is no public evidence of active exploitation, but the vulnerability's potential impact warrants immediate remediation.
Where can I find the official JupyterLab advisory for CVE-2026-42266?
Refer to the official JupyterLab security advisory, which can be found on the JupyterLab GitHub repository and the NVD database (search for CVE-2026-42266).
Is your project affected?
Upload your dependency file and we'll tell you instantly if this and other CVEs hit you.
Detect this CVE in your project
Upload your requirements.txt file and we'll tell you instantly if you're affected.
Scan your Python project now — no account
Upload your requirements.txt and get the vulnerability report instantly. No account. Uploading the file is just the start: with an account you get continuous monitoring, Slack/email alerts, multi-project and white-label reports.
Drag & drop your dependency file
composer.lock, package-lock.json, requirements.txt, Gemfile.lock, pubspec.lock, Dockerfile...