CVE-2021-41134 is a medium-severity (CVSS 5.4) Cross-site Scripting (XSS) vulnerability in nbdime. A fix is available for nbdime — see the affected versions and patch details below.
Stored XSS in Jupyter nbdime
EPSS Exploitation Probability
Probability of exploitation in the next 30 days, from FIRST.org EPSS.
How urgent is this, really
CVE-2021-41134 by exploitation likelihood (EPSS) against impact (CVSS). Outside the shaded patch-first corner.
Where this sits among everything scored
Of 385,738 CVEs with a current EPSS score, this one falls in the < 10% band (highlighted). Counts from FIRST.org, log-scaled.
Real-World Exposure
How broadly this vulnerability is actually deployed: weekly install volume shows current usage, and reverse-dependency count shows how many other packages break if it stays unpatched.
nbdimenpmnbdime-jupyterlabnpmDescription
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 Packages
| Ecosystem | Package | Vulnerable range | Fix |
|---|---|---|---|
| 📦npm | nbdime | all versions | 5.0.2npm install nbdime@5.0.2 |
| 📦npm | nbdime | ≥ 6.0.0&&< 6.1.2 | 6.1.2npm install nbdime@6.1.2 |
| 📦npm | nbdime-jupyterlab | all versions | 1.0.1npm install nbdime-jupyterlab@1.0.1 |
| 📦npm | nbdime-jupyterlab | ≥ 2.0.0&&< 2.1.1 | 2.1.1npm install nbdime-jupyterlab@2.1.1 |
| 🐍PyPI | nbdime | all versions | 1.1.1pip install --upgrade 'nbdime==1.1.1' |
| 🐍PyPI | nbdime | ≥ 2.0.0&&< 2.1.1 | 2.1.1pip install --upgrade 'nbdime==2.1.1' |
Affected Products
nbdimejupyternbdime-jupyterlabjupyterDetection & mitigation playbook
Open-source dependencyDetect
Scan your dependency tree (package-lock.json, pnpm-lock.yaml, requirements.txt, go.sum, etc.) for nbdime, including transitive dependencies — a direct dependency you never call can still pull in a vulnerable version.
Fix
Update nbdime to 5.0.2 or later, then make sure no transitive (indirect) dependency still pins the vulnerable range — O3 confirms CVE-2021-41134 is resolved across your whole dependency graph.
Workarounds
Escape or sanitise the affected output on the server side rather than relying on client-side filtering, and add a Content-Security-Policy that blocks inline script execution so injected markup cannot run even if it reaches the page.
Frequently Asked Questions
Is CVE-2021-41134 in your dependencies?
Find it across npm, PyPI, including transitive dependencies.