CVE-2026-40171

Description

In Jupyter Notebook versions 7.0.0 through 7.5.5, JupyterLab versions 4.5.6 and earlier, and the corresponding @jupyter-notebook/help-extension and @jupyterlab/help-extension packages before 7.5.6 and 4.5.7, a stored cross-site scripting issue in the help command linker can be chained with attacker-controlled notebook content to steal authentication tokens with a single click. An attacker can craft a malicious notebook file containing elements that appear indistinguishable from legitimate controls and trigger execution when a user interacts with them. Successful exploitation allows theft of the user's authentication token and complete takeover of the Jupyter session through the REST API, including reading files, creating or modifying files, accessing kernels to execute arbitrary code, and creating terminals for shell access. This issue has been fixed in Notebook 7.5.6, JupyterLab 4.5.7, @jupyter-notebook/help-extension 7.5.6, and @jupyterlab/help-extension 4.5.7. As a workaround, disable the affected help extensions or set allowCommandLinker to false in the sanitizer configuration.

How to fix CVE-2026-40171

To remediate CVE-2026-40171, upgrade the affected package to a fixed version below.

—upgrade to 7.5.6 or later
—upgrade to 7.5.6 or later
—upgrade to 4.5.7 or later
—upgrade to 4.5.7 or later
—upgrade to 4.5.7 or later
—upgrade to 7.5.6 or later
—upgrade to 7.5.6 or later
—upgrade to 7.5.6 or later
—upgrade to 4.5.7 or later

Is CVE-2026-40171 being exploited?

Low — EPSS is 0.5%, meaning exploitation activity has not been observed at scale.

Affected packages (9)

>= 7.0.0, < 7.5.6
>= 7.0.0, < 7.5.6
from 0, < 4.5.7
from 0, < 4.5.7
from 0, < 4.5.7
>= 7.0.0, < 7.5.6
>= 7.0.0, < 7.5.6
>= 7.0.0, < 7.5.6
from 0, < 4.5.7

CVSS scores

Source	Version	Severity	Vector
osv	CVSS 4.0	—	CVSS:4.0/AV:N/AC:L/AT:N/PR:H/UI:A/VC:H/VI:H/VA:H/SC:N/SI:N/SA:N