CVE-2026-54527 is a critical stored cross-site scripting flaw (CVSS 9.0) in the jupyterlab-git extension from 0.30.0b3 before 0.54.0. A crafted filename in a rename commit runs script when someone views the rename diff in the Git History tab. Upgrade to jupyterlab-git 0.54.0.
What's affected
- jupyterlab-git from 0.30.0b3 up to but not including 0.54.0, per the record.
- Fixed in 0.54.0. The release notes list this CVE and CVE-2026-54528 under security fixes.
- Anyone who opens commit history of repositories they did not create, on a JupyterLab server.
How to check if you're exposed
Check the installed extension version in each environment.
pip show jupyterlab-git
jupyter labextension list
If the version is 0.30.0b3 or later but below 0.54.0, you are exposed. Pay attention to shared JupyterLab servers, since a victim there can have a terminal available in the same session.
What to do now
- Raise the jupyterlab-git requirement to 0.54.0 or later, reinstall, and restart JupyterLab.
- Rebuild images and environments that pin an older version.
- Until then, avoid opening the rename diff view for repositories from untrusted sources.
- Review the other security fix in 0.54.0, CVE-2026-54528.
Why it matters
The class is CWE-79, cross-site scripting. The advisory says the diff header code passed Git filenames straight into an HTML property when rendering renamed files, so a filename that contained markup was treated as markup.
The score is high because script in a JupyterLab page runs with the user's session, and JupyterLab can start terminals. The advisory credits Amazon Web Services Security with the report. The record does not mark the CVE as exploited in the wild. Filenames are input like any other, so they need escaping too.
For your own projects, the free in-browser dependency scan needs no install, and the Gold directory tracks this CVE.
Quick check
Can I be hit just by cloning a repository?
The advisory describes a user cloning, opening the Git History tab, clicking the rename commit and then the renamed file. Those steps are needed.
Sources
- https://github.com/jupyterlab/jupyterlab-git/security/advisories/GHSA-f962-v9hr-pfg5
- https://github.com/jupyterlab/jupyterlab-git/releases/tag/v0.54.0
Last reviewed: 19 October 2026.
