CVE-2026-44727 | Jupyter Server is the backend for Jupyter web applications. … | CVSS 9.3 CRITICAL

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.

Metadata

CVE ID: CVE-2026-44727
State: PUBLISHED
Assigner: GitHub_M
Reserved: 2026-05-07 18:04 UTC
Published: 2026-06-22 19:56 UTC
Last updated: 2026-06-22 19:56 UTC
Primary CWE: CWE-79
CWE-79: Improper Neutralization of Input During Web Page Gen…
Vendor / Product: jupyter-server / jupyter_server
Sources: cve.org · NVD

Severity & Metrics

9.3 CRITICAL CVSS 4.0

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

Affected products (1)

Vendor	Product	Platform	Versions
jupyter-server	jupyter_server	—	< 2.20

Weakness (CWE)

CWE	Source	Description
CWE-1021	cna	CWE-1021: Improper Restriction of Rendered UI Layers or Frames
CWE-79	cna	CWE-79: Improper Neutralization of Input During Web Page Generation ('Cross-site Scripting')

CVSS scores (1)

Score	Severity	Version	Source	Vector
9.3	CRITICAL	4.0	cna	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

References (2)

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