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.
History

Tue, 30 Jun 2026 00:45:00 +0000

Type Values Removed Values Added
References
Metrics threat_severity

None

cvssV3_1

{'score': 9.0, 'vector': 'CVSS:3.1/AV:N/AC:L/PR:L/UI:R/S:C/C:H/I:H/A:H'}

threat_severity

Important


Wed, 24 Jun 2026 16:45:00 +0000

Type Values Removed Values Added
First Time appeared Jupyter
Jupyter jupyter Server
Vendors & Products Jupyter
Jupyter jupyter Server

Tue, 23 Jun 2026 13:30:00 +0000

Type Values Removed Values Added
Metrics ssvc

{'options': {'Automatable': 'no', 'Exploitation': 'none', 'Technical Impact': 'total'}, 'version': '2.0.3'}


Mon, 22 Jun 2026 21:00:00 +0000

Type Values Removed Values Added
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.
Title Jupyter Server: Stored XSS in `NbconvertFileHandler` / `NbconvertPostHandler` via missing `sandbox` CSP
Weaknesses CWE-1021
CWE-79
References
Metrics cvssV4_0

{'score': 9.3, 'vector': 'CVSS:4.0/AV:N/AC:L/AT:N/PR:L/UI:A/VC:H/VI:H/VA:H/SC:H/SI:H/SA:H'}


cve-icon MITRE

Status: PUBLISHED

Assigner: GitHub_M

Published: 2026-06-22T19:56:56.776Z

Updated: 2026-07-08T12:06:12.875Z

Reserved: 2026-05-07T18:04:17.309Z

Link: CVE-2026-44727

cve-icon Vulnrichment

Updated: 2026-07-08T12:06:12.875Z

cve-icon NVD

No data.

cve-icon Redhat

Severity : Important

Publid Date: 2026-06-22T19:56:56Z

Links: CVE-2026-44727 - Bugzilla