Jupyter Notebook and JupyterLab token theft via stored XSS in help command linker

Summary

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.

Timeline

1. May 6, 2026, 7:36 PM UTCCVE published
2. May 7, 2026, 12:00 AM UTCCISA SSVC assessment

   Exploitation: none · Automatable: no · Technical impact: total

3. May 8, 2026, 3:55 AM UTCRecord last updated

Affected versions

• jupyter notebook

  From 7.0.0 · through 7.5.5

• jupyterlab help-extension

  through 4.5.6

• jupyterlab jupyterlab

  through 4.5.6

• jupyter-notebook help-extension

  From 7.0.0 · through 7.5.5

• @jupyter-notebook/help-extensionnpm

  From 7.0.0 · fixed in 7.5.6

• notebookPyPI

  From 7.0.0 · fixed in 7.5.6

• jupyterlabPyPI

  fixed in 4.5.7

• @jupyterlab/help-extensionnpm

  fixed in 4.5.7

References 1