Cross-site scripting in Jupyter Server - CVE-2026-44727
Published: September 3, 2026
Vulnerability identifier: #VU146866
CSH Severity: Low
CVSS v4: 5.1 [CVSS:4.0/AV:N/AC:L/AT:N/PR:L/UI:P/VC:N/VI:N/VA:N/SC:L/SI:L/SA:N]
CVE-ID: CVE-2026-44727
CWE-ID: CWE-79
Exploitation vector: Remote access
Exploit availability:
No public exploit available
Vulnerability details
The vulnerability allows a local user to execute arbitrary code.
The vulnerability exists due to cross-site scripting in NbconvertFileHandler and NbconvertPostHandler when rendering user-authored notebook HTML under the Jupyter origin without a sandbox directive in the Content-Security-Policy. A local user can place crafted HTML payloads in a notebook display_data output to execute arbitrary code.
User interaction is required because an authenticated victim must navigate to a /nbconvert/html/<path> view containing attacker-authored output.
Affected software
Jupyter Server
Fedora
python-jupyter-server
Fedora
python-jupyter-server
How to mitigate CVE-2026-44727
Install security update from vendor's website.
Jupyter Server - update to 2.20.0
python-jupyter-server - update to 2.20.0-1.fc43
python-jupyter-server - update to 2.20.0-1.fc43