CVE-2026-44727
CRITICAL 9.3Jupyter 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.
Severe if exploited (CVSS 9.3), but no known exploitation and low modeled probability. Patch on a normal cadence.
Exploitation likelihood
0.2%chance of exploitation in 30 days · 13th percentile
Impact if exploited
9.3CVSS 4.0 · CRITICAL
- ConfidentialityHigh
- IntegrityHigh
- AvailabilityHigh
What an attacker needs
- ✓Access: Reachable over the network — no local access needed
- ⚠Privileges: Requires a low-privilege account
- ⚠User interaction: Requires active user interaction
- ✓Complexity: No special conditions — reliably repeatable
- ✓Requirements: No special attack requirements
✓ lowers the bar for an attacker · ⚠ raises it
Affected
Vendors Jupyter Server Red Hat
Products Jupyter Server Migration Toolkit For Applications 8 Red Hat Openshift Ai (Rhoai)
Weakness (CWE)
- CWE-79: Cross-site scripting (XSS)
- CWE-1021
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
References
Technical & other
- https://github.com/jupyter-server/jupyter_server/security/advisories/GHSA-fcw5-x6j4-ccmp
- https://github.com/jupyter-server/jupyter_server/commit/6cbee8d65e71abac851c4492fea987ad080580bd
- https://access.redhat.com/security/cve/CVE-2026-44727
- https://bugzilla.redhat.com/show_bug.cgi?id=2491516
- https://security.access.redhat.com/data/csaf/v2/vex/2026/cve-2026-44727.json