Review reviewCritical

CVE-2026-44727

jupyter-server jupyter_server, Red Hat Migration Toolkit for Applications 8.2, Red Hat OpenShift AI (RHOAI)

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.

CVSS: 9.3
EPSS: 0.30%
CISA KEV: Not listed
Published: 2026.06.23

PRIORITY ASSESSMENT

Review review

The CVSS severity warrants an early asset and exposure review.

Known exploitationNot established by KEV

Exploit probability0.30%

Technical severityCVSS 9.3

Vulnerability overview

Affected product and versions

Product: jupyter-server jupyter_server, Red Hat Migration Toolkit for Applications 8.2, Red Hat OpenShift AI (RHOAI)
Affected versions: >= < 2.20, < 2.20.0
Fixed versions: 2.20.0

Recommended response sequence

Confirm exposure before applying a vendor-supported change.

Full remediation guide

1
Identify
Confirm that jupyter-server jupyter_server, Red Hat Migration Toolkit for Applications 8.2, Red Hat OpenShift AI (RHOAI) and an affected version are present.
2
Prioritize
Combine exploitation signals with asset exposure and business criticality.
3
Remediate
Follow the vendor advisory or supported update path and preserve rollback options.
4
Verify
Recheck the version, service health, access paths, and relevant logs.

Technical data

CVSS 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/E:X/CR:X/IR:X/AR:X/MAV:X/MAC:X/MAT:X/MPR:X/MUI:X/MVC:X/MVI:X/MVA:X/MSC:X/MSI:X/MSA:X/S:X/AU:X/R:X/V:X/RE:X/U:X
CWE: CWE-1021, CWE-79