CVE-2021-41134: Stored XSS in Jupyter nbdime

Severity: medium (CVSS 5.4 v3.1)
Exploited in the wild: not listed in CISA KEV
EPSS: 0.7% probability of exploitation in the next 30 days
Public exploit or detection template: none known
Published: 2021-11-03 · updated 2026-06-17
Weakness: CWE-79

Description

nbdime provides tools for diffing and merging of Jupyter Notebooks. In affected versions a stored cross-site scripting (XSS) issue exists within the Jupyter-owned nbdime project. It appears that when reading the file name and path from disk, the extension does not sanitize the string it constructs before returning it to be displayed. The diffNotebookCheckpoint function within nbdime causes this issue. When attempting to display the name of the local notebook (diffNotebookCheckpoint), nbdime appears to simply append .ipynb to the name of the input file. The NbdimeWidget is then created, and the base string is passed through to the request API function. From there, the frontend simply renders the HTML tag and anything along with it. Users are advised to patch to the most recent version of the affected product.

Affected products

jupyter nbdime: from 1.0.0 before 1.1.1; from 2.0.0 before 2.1.1; from 3.0.0 through 3.1.1; from 5.0.0 before 5.0.2; from 6.0.0 before 6.1.2 — fixed in 1.1.1, 2.1.1, 5.0.2, 6.1.2
jupyter Nbdime-Jupyterlab: from 1.0.0 before 1.0.1; from 2.0.0 before 2.1.1 — fixed in 1.0.1, 2.1.1

How to fix

Upgrade to a fixed version: jupyter nbdime 1.1.1, 2.1.1, 5.0.2, 6.1.2; jupyter Nbdime-Jupyterlab 1.0.1, 2.1.1. Check the vendor advisory for mitigations.

References

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