9.3Critical
CVE-2026-44727Jupyter Server: Stored XSS in `NbconvertFileHandler` / `NbconvertPostHandler` via missing `sandbox` CSP
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.
Data: CVE.org, NVD, CISA KEV, FIRST EPSS, Ubuntu. Published as the sources state it, in English.
Affected products and versions
| Vendor | Product | Versions | |
|---|---|---|---|
| jupyter | jupyter server | < 2.20.0 | |
| jupyter-server | jupyter_server | < 2.20 | |
| migration toolkit applications | 8.2 | — | |
| openshift ai | 3.4 | — | |
| Red Hat | Red Hat Migration Toolkit for Applications 8.2 | all versions | |
| Red Hat | Red Hat OpenShift AI 3.4 | all versions | |
| Red Hat | Red Hat OpenShift AI (RHOAI) | all versions |
References and patches
- https://github.com/jupyter-server/jupyter_server/security/advisories/GHSA-fcw5-x6j4-ccmp MitigationPatchVendor Advisory
- https://github.com/jupyter-server/jupyter_server/commit/6cbee8d65e71abac851c4492fea987ad080580bd Patch
- https://access.redhat.com/errata/RHSA-2026:43038
- https://access.redhat.com/errata/RHSA-2026:60520
- 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
CPE matches (NVD) (1)
cpe:2.3:a:jupyter:jupyter_server:*:*:*:*:*:*:*:*< 2.20.0