Stored XSS and Remote Code Execution in Jupyter Server
CVE-2026-44727

9.3CRITICAL

Key Information:

Vendor

Jupyter-server

Status
Jupyter Server
Vendor
CVE Published:
22 June 2026

What is CVE-2026-44727?

Jupyter Server's handling of user-authored notebook HTML prior to version 2.20 in its nbconvert HTTP handlers poses significant security risks. The absence of a proper sandbox directive within the Content-Security-Policy coupled with nbconvert.HTMLExporter's default non-sanitizing behavior enables an attacker to exploit notebooks containing malicious HTML payloads. This exploitation can lead to stored XSS, allowing unauthorized access to cookies and full authority over API endpoints, as well as the potential for kernel remote code execution. The vulnerability has been addressed in version 2.20, mitigating these risks.

Affected Version(s)

jupyter_server < 2.20

References

https://github.com/jupyter-server/jupyter_server/security...
x_refsource_CONFIRM
https://github.com/jupyter-server/jupyter_server/commit/6...
x_refsource_MISC

CVSS V4

Score:
9.3
Severity:
CRITICAL
Confidentiality:
High
Integrity:
High
Availability:
High
Attack Vector:
Network
Attack Complexity:
Low
Attack Required:
None
Privileges Required:
Undefined
User Interaction:
Unknown

Timeline

  • Vulnerability published

  • Vulnerability Reserved

.