Vulnerability Description
Jupyter Server is the backend for Jupyter web applications. Prior to 2.20, the nbconvert HTTP handlers in jupyter_server render user-authored notebook HTML under the Jupyter origin without a sandbox directive in their Content-Security-Policy. Combined with nbconvert.HTMLExporter's default non-sanitizing behavior, a notebook carrying an HTML payload in a display_data output triggers stored XSS with cookie access, full /api/* authority, and kernel RCE. This vulnerability is fixed in 2.20.
CVSS Score
MEDIUM
Affected Products
| Vendor | Product | Versions |
|---|---|---|
| Jupyter | Jupyter Server | < 2.20.0 |
Related Weaknesses (CWE)
References
- https://github.com/jupyter-server/jupyter_server/commit/6cbee8d65e71abac851c4492Patch
- https://github.com/jupyter-server/jupyter_server/security/advisories/GHSA-fcw5-xMitigationPatchVendor Advisory
- https://access.redhat.com/errata/RHSA-2026:43038
- https://access.redhat.com/security/cve/CVE-2026-44727
- https://bugzilla.redhat.com/show_bug.cgi?id=2491516
- https://security.access.redhat.com/data/csaf/v2/vex/2026/cve-2026-44727.json
FAQ
What is CVE-2026-44727?
CVE-2026-44727 is a vulnerability with a CVSS score of 5.4 (MEDIUM). Jupyter Server is the backend for Jupyter web applications. Prior to 2.20, the nbconvert HTTP handlers in jupyter_server render user-authored notebook HTML under the Jupyter origin without a sandbox d...
How severe is CVE-2026-44727?
CVE-2026-44727 has been rated MEDIUM with a CVSS base score of 5.4/10. Review the CVSS metrics above for detailed severity breakdown.
Is there a patch for CVE-2026-44727?
Check the references section above for vendor advisories and patch information. Affected products include: Jupyter Jupyter Server.