SB2026090354 - Cross-site scripting in Jupyter Server

Description

This security bulletin contains information about 1 vulnerability.

1) Cross-site scripting (CVE-ID: CVE-2026-44727)

CWE-ID: CWE-79 - Improper Neutralization of Input During Web Page Generation ('Cross-site Scripting')

CVSSv4: 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]

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.

Remediation

Install update from vendor's website.

References

• https://github.com/jupyter-server/jupyter_server/security/advisories/GHSA-fcw5-x6j4-ccmp
• https://github.com/jupyter-server/jupyter_server/commit/6cbee8d65e71abac851c4492fea987ad080580bd