CVE-2026-44727
Medium
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.
SeverityMedium
CVSS5.4
Exploit probability—
ProductJupyter Server
PublishedJun 22, 2026
First seenJun 22, 2026
Weakness typeCWE-79Cross-site scripting (XSS)CWE-1021CWE-1021
How to fix
Update
- jupyter jupyter_server2.20.0 or later
- jupyter-server2.20.0 or later
Affected products
| Product | Affected versions | Fixed in |
|---|---|---|
| jupyter jupyter_server | v < 2.20.0 | 2.20.0 |
| jupyter-serverPyPI | v < 2.20.0 | 2.20.0 |
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