Jupyter Server: Stored XSS in `NbconvertFileHandler` / `NbconvertPostHandler` via missing `sandbox` CSP
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.
Impact
An authenticated victim who navigates to /nbconvert/html/<path> containing attacker-authored output can have their token exfiltrated to another domain because it is executed in the Jupyter origin.
Patches
Fixed in v2.20.0, commit 6cbee8d
Workarounds
For deployments where editing the installed jupyter_server is impractical (containerized builds, read-only images), adding this to jupyter_server_config.py has the same effect as the patch above without touching source files:
import jupyter_server.nbconvert.handlers as _nb
def _csp(self):
return super(type(self), self).content_security_policy + "; sandbox allow-scripts"
_nb.NbconvertFileHandler.content_security_policy = property(_csp)
_nb.NbconvertPostHandler.content_security_policy = property(_csp)Software afectado
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| Plataforma | Paquete | Versiones vulnerables | Corregida en |
|---|---|---|---|
| Python (PyPI) | jupyter-server | < 2.20.0 | 2.20.0 |
Referencias
- 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
- https://pypi.org/project/jupyter-server
- https://github.com/advisories/GHSA-fcw5-x6j4-ccmp
- https://nvd.nist.gov/vuln/detail/CVE-2026-44727
- 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://github.com/pypa/advisory-database/tree/main/vulns/jupyter-server/PYSEC-2026-366.yaml
- https://security.access.redhat.com/data/csaf/v2/vex/2026/cve-2026-44727.json
- Vector CVSS
CVSS:3.1/AV:N/AC:L/PR:L/UI:R/S:C/C:L/I:L/A:N- Debilidad (CWE)
CWE-1021, CWE-79- Plataforma
- Python (PyPI)
- Paquete
jupyter-server- Publicada
- 18.06.2026
- Actualizado
- 11.10.2026 15:17
Fuentes y licencias
OSV / GitHub Advisory Database - PYSEC-2026-366 - PyPA Advisory Database; CC BY 4.0
OSV / GitHub Advisory Database - GHSA-fcw5-x6j4-ccmp - CC BY 4.0
Historial de vulnerabilidades: jupyter-server
Todas las vulnerabilidades publicadas de este paquete (Python (PyPI)), de la más reciente a la más antigua. Muestra si es un fallo aislado o un paquete que hay que vigilar.
- Entradas en total
- 14
- Primera → última
- 11.2020 09.2026
- Sin corrección
- 0
- Explotada en ataques
- 0
Distribución por gravedad
- Crítica 1
- Alta 7
- Media 6
Divulgaciones por año
- 2020: 2
- 2021: 0
- 2022: 2
- 2023: 3
- 2024: 1
- 2025: 0
- 2026: 6
-
Jupyter Server: Stored XSS in `NbconvertFileHandler` / `NbconvertPostHandler` via missing `sandbox` CSP esta entrada
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