Jupyter: Jupyter Server: Stored XSS in `NbconvertFileHandler` / `NbconvertPostHandler` via missing…
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- Severity
- Medium, CVSS 5.4
- CVSS vector
- CVSS:3.1/AV:N/AC:L/PR:L/UI:R/S:C/C:L/I:L/A:N
- Record
- CVE-2026-44727
- Affects
- Jupyter
- Known exploited
- Not listed in the CISA Known Exploited Vulnerabilities catalog
- Published
- Record first published by the source
- June 22, 2026
- Source last modified
- October 25, 2026
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.
Description quoted from the NVD record.