CVE-2026-44727
MediumCVSS 5.4Exploitation Probability (EPSS)
Low risk13th percentile — higher than 13% of all known CVEs
Summary
A vulnerability in Jupyter Server before version 2.20 allows stored XSS via malicious HTML in notebook display_data output. Missing sandbox directive in Content-Security-Policy for nbconvert endpoints enables script execution under Jupyter origin, leading to session hijacking and remote code execution.
Risk Assessment
An attacker can steal session cookies, gain full access to Jupyter API, and execute arbitrary code in the kernel, potentially compromising the entire server and data.
Recommendation
Upgrade Jupyter Server to version 2.20 or later immediately. If upgrade is not possible, restrict access to nbconvert endpoints and apply additional CSP protections.
Original NVD description (English source)
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.