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CVE-2026-44727

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

Description (CNA)

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.

Affected (CNA)

Vendor / productVersions
jupyter-server / jupyter_serveraffected < 2.20

CWE

CWE-79, CWE-1021

References

ADP enrichment

CISA-ADP

No English description supplied.

No references supplied.

redhat-SADP

A flaw was found in Jupyter Server. The nbconvert HTTP handlers in Jupyter Server render user-authored notebook HTML without a sandbox directive in their Content-Security-Policy. This, combined with nbconvert.HTMLExporter's default non-sanitizing behavior, allows a notebook containing an HTML payload to trigger a stored Cross-Site Scripting (XSS) vulnerability. A remote attacker could exploit this to gain cookie access, full API authority, and achieve kernel Remote Code Execution (RCE).