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BIT-jupyterlab-2026-40171 — Jupyter Notebook and JupyterLab token theft via stored XSS in help command linker

2026-10-01T01:43:01.593958+00:00

Affected: Bitnami: jupyterlab

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.

CVE-2026-40171 — Jupyter Notebook and JupyterLab token theft via stored XSS in help command linker

2026-10-01T01:43:01.594032+00:00

Affected: jupyter notebook, jupyterlab help-extension, jupyterlab, jupyter-notebook help-extension

GHSA-rch3-82jr-f9w9 — Jupyter Notebook Vulnerable to Authentication Token Theft via CommandLinker XSS

2026-10-01T01:43:01.594078+00:00

Affected: npm: @jupyter-notebook/help-extension, PyPI: notebook, PyPI: jupyterlab, npm: @jupyterlab/help-extension

### Impact

A stored Cross-Site Scripting (XSS) vulnerability in Jupyter Notebook allows attackers to steal authentication tokens from users who open malicious notebook files and interact with elements that the attacker can make look indistinguishable from legitimate controls (single click interaction).

The vulnerability enables complete account takeover through the Jupyter REST API, allowing the attacker to: 1. Read all files 2. Modify/create files 3. Access running kernels and execute arbitrary code 4. Create terminals for shell access

### Patches

Jupyter Notebook 7.5.6 and JupyterLab 4.5.7 include patches for this vulnerability.

### Workarounds

The help extension can be disabled via CLI:

``` jupyter labextension disable @jupyter-notebook/help-extension jupyter labextension disable @jupyterlab/help-extension ```

### Hardening

The patched versions include a toggle to disable the command linker functionality altogether, for example via `overrides.json`:

```json { "@jupyterlab/apputils-extension:sanitizer": { "allowCommandLinker": false } } ```

### Resources

- https://jupyterlab.readthedocs.io/en/latest/user/commands.html#commands-in-markdown-output-and-files

### Acknowledgments

Reported by Daniel Teixeira - NVIDIA AI Red Team

PYSEC-2026-2538 — Jupyter Notebook Vulnerable to Authentication Token Theft via CommandLinker XSS

2026-10-01T01:43:01.594128+00:00

Affected: PyPI: jupyterlab