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CVE-2026-44727

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

Published: Jun 22, 2026Updated: Jul 22, 2026 Sources: CVE List NVDCWE-79
5.4MEDIUM
NVD MITRE
EPSS Score
0.3%
Top 77.2%
CISA KEV
Not in KEV
Exploits
No Known Exploits
Remediation
Patch Available
Self-Check
OpenVAS

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.

No summary for this CVE yet.

CVSS Vector Breakdown

AV:NAC:LPR:LUI:RS:CC:LI:LA:N
Exploitability
AV:NAttack Vector
Network
AC:LAttack Complexity
Low
PR:LPrivileges Required
Low
UI:RUser Interaction
Required
Scope
S:CScope
Changed
Impact
C:LConfidentiality
Low
I:LIntegrity
Low
A:NAvailability
None
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Weaknesses

CWE-79CWE-1021

Affected Products

jupyter
oss-projectaka jupyter server, notebook, jupyterlab
jupyter serverOn-premWeb App
AI / ML / notebook-mlops
jupyter-server
oss-project·USaka jupyter-scheduler, jupyter_server
jupyter_serverOn-prem
AI / ML / notebook-mlops

Exploitability

Official Patch Available
Workaround Available
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Attack Graph

Products CVE Techniques Tactics

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MITRE ATT&CK

2 techniques
Execution
Initial Access
View detailed technique mapping

References

https://github.com/jupyter-server/jupyter_server/commit/6cbee8d65e71abac851c4492fea987ad080580bd
github.com
https://github.com/jupyter-server/jupyter_server/security/advisories/GHSA-fcw5-x6j4-ccmp
github.com
https://access.redhat.com/errata/RHSA-2026:43038
access.redhat.com
and 3 more references View all →

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