A stored cross‑site scripting vulnerability in the help command linker allows an attacker to embed malicious notebook content that, when viewed or interacted with by a user, steals the authentication token. Possession of the token gives the attacker full control over the Jupyter session through the REST API, enabling them to read or modify files, execute arbitrary code, and create terminal sessions. The weakness is a classic cross‑site scripting flaw (CWE‑79).

The vulnerability affects Jupyter Notebook versions 7.0.0 through 7.5.5 and JupyterLab versions 4.5.6 and earlier. It also affects the @jupyter-notebook/help-extension package prior to 7.5.6 and the @jupyterlab/help-extension package prior to 4.5.7. All products listed are identified in the advisories for Jupyter Notebook and JupyterLab. If you are running any version within those ranges, you are at risk.

The CVSS score of 8.4 indicates a high‑severity flaw and the lack of an EPSS score does not diminish the documented attack path. The vulnerability can be exploited by placing a malicious notebook on the server, after which a user’s single click on a hidden link in the help section triggers token theft. The attacker then rolls the full functionality of the Jupyter REST API to maintain a persistent foothold. The vulnerability is not listed in the CISA KEV catalog; however, its impact is significant for any environment where Jupyter is used for data science or notebook collaboration.