Jupyter JupyterLab/JupyterLite Plural Forms cross site scripting

Summaryinfo

A vulnerability categorized as problematic has been discovered in Jupyter JupyterLab and JupyterLite. The affected element is an unknown function of the component Plural Forms. Such manipulation leads to cross site scripting. This vulnerability is uniquely identified as CVE-2026-102830. The attack can be launched remotely. No exploit exists.

Detailsinfo

A vulnerability was found in Jupyter JupyterLab and JupyterLite (affected version unknown) and classified as problematic. Affected by this issue is an unknown functionality of the component Plural Forms. The manipulation with an unknown input leads to a cross site scripting vulnerability. Using CWE to declare the problem leads to CWE-79. The product does not neutralize or incorrectly neutralizes user-controllable input before it is placed in output that is used as a web page that is served to other users. Impacted is integrity. CVE summarizes:

JupyterLab is an extensible environment for interactive and reproducible computing, based on the Jupyter Notebook Architecture. From JupyterLab 3.0.0 until 4.5.11 and 4.6.4, and in JupyterLite Core 0.8.3 and earlier, the Plural-Forms header in a selected third-party language pack can append JavaScript after a valid plural rule because prefix-only regular-expression validation accepts a matching prefix without requiring the entire header to match. JupyterLab passes the accepted expression to new Function, so loading the catalogue and translating a plural string executes the appended code in the authenticated JupyterLab origin. Where Jupyter Server kernels, terminals, and APIs are exposed, the code can use authenticated server APIs to read or modify files and run code. Impact is much more limited in JupyterLite because it typically lacks most exposed Jupyter Server surfaces. The default English locale is unaffected because it does not load a translation catalogue. This issue is fixed in JupyterLab 4.5.11 and 4.6.4 and JupyterLite Core 0.8.4.

The advisory is shared for download at github.com. This vulnerability is handled as CVE-2026-102830 since 09/29/2026. The exploitation is known to be easy. The attack may be launched remotely. Successful exploitation requires user interaction by the victim. There are neither technical details nor an exploit publicly available. The MITRE ATT&CK project declares the attack technique as T1059.007.

There is no information about possible countermeasures known. It may be suggested to replace the affected object with an alternative product.

Once again VulDB remains the best source for vulnerability data.

Productinfo

Vendor

• Jupyter

Name

• JupyterLab
• JupyterLite

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