Client-Side Enforcement of Server-Side Security Affecting jupyterlab package, versions [,4.5.7)[4.6.0a4, 4.6.0a5)
Threat Intelligence
The probability is the direct output of the EPSS model, and conveys an overall sense of the threat of exploitation in the wild. The percentile measures the EPSS probability relative to all known EPSS scores. Note: This data is updated daily, relying on the latest available EPSS model version. Check out the EPSS documentation for more details.
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Test your applications- Snyk IDSNYK-PYTHON-JUPYTERLAB-16425771
- published6 May 2026
- disclosed5 May 2026
- creditPhuong Cao
Introduced: 5 May 2026
CVE-2026-42266 (opens in a new tab)How to fix?
Upgrade jupyterlab to version 4.5.7, 4.6.0a5 or higher.
Overview
jupyterlab is a JupyterLab computational environment.
Affected versions of this package are vulnerable to Client-Side Enforcement of Server-Side Security via improper enforcement of the allowed_extensions_uris. An attacker can gain unauthorized access to install unapproved extensions by sending crafted POST requests. This can lead to privilege escalation, data exfiltration, lateral movement within the network, and persistent compromise of the server infrastructure.
Note: This is only exploitable if the PyPI Extension Manager is enabled and the deployment relies on allow-listed extensions for security.
Workaround
This vulnerability can be mitigated by switching the extension manager to read-only mode using the command line option '--LabApp.extension_manager=readonly' or by setting the traitlet 'c.LabApp.extension_manager = "readonly"'.