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CVE

CVE-2026-44727

Jupyter Server: Stored XSS in `NbconvertFileHandler` / `NbconvertPostHandler` via missing `sandbox` CSP
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CVE

CVE-2026-44727

Jupyter Server: Stored XSS in `NbconvertFileHandler` / `NbconvertPostHandler` via missing `sandbox` CSP

Jupyter Server is the backend for Jupyter web applications. Prior to 2.20, the nbconvert HTTP handlers in jupyterserver 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 displaydata output triggers stored XSS with cookie access, full /api/* authority, and kernel RCE. This vulnerability is fixed in 2.20.

Package Versions Affected

Package Version
patch Availability
No items found.

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CVSS Version

Severity
Base Score
CVSS Version
Score Vector
C
H
U
9.3
-
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/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
C
H
U
0
-
C
H
U
8.2
-
3.1
CVSS:3.1/AV:L/AC:L/PR:L/UI:R/S:C/C:H/I:H/A:H

Related Resources

No items found.

References

https://security.access.redhat.com/data/csaf/v2/vex/2026/cve-2026-44727.json, 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://github.com/CVEProject/cvelistV5/tree/main/cves/2026/44xxx/CVE-2026-44727.json, https://github.com/jupyter-server/jupyterserver/security/advisories/GHSA-fcw5-x6j4-ccmp, https://nvd.nist.gov/vuln/detail/CVE-2026-44727, https://bugzilla.redhat.com/showbug.cgi?id=2491516, https://github.com/jupyter-server/jupyter_server/commit/6cbee8d65e71abac851c4492fea987ad080580bd

Severity

0

CVSS Score
0
10

Basic Information

Base CVSS
0
EPSS Probability
0.00438%
EPSS Percentile
0.37287%
Introduced Version
0
Fix Available
6cbee8d65e71abac851c4492fea987ad080580bd,2.21.0-r6

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