Vulnerability Analysis
Jupyter Server: Stored XSS in `NbconvertFileHandler` / `NbconvertPostHandler` via missing `sandbox` CSP
CVE-2026-44727
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.
Cross-Site Scripting (XSS)
No Active Exploit Signals
CVSS Base Score
9.3
CRITICAL
Exploitability:-
Impact Score:-
Temporal Score:-
EPSS:0.23%
Threat Intelligence Signals
CISA KEV
No
KEV Date Added
—
Ransomware Use
—
KEV Due Date
—
VulnCheck In-the-Wild
No
Nuclei Template
No
EPSS Score
0.227%
EPSS Percentile
13.5th pct
GHSA ID
GitHub Severity
CRITICAL
SSVC Exploitation
None
SSVC Automatable
No
Vulnerability Class
Cross-Site Scripting (XSS)
Identity & Timeline
| Status | - |
| Assigning Authority | - |
| CVSS Version / Source | - |
| Reserved | - |
| Published | - |
| Patch Date (date_public) | - |
| Exploit DB Date | - |
| First GitHub PoC Date | - |
| Last Updated | - |
| Time to Patch (Days to fix) | - |
| Exploit Release Gap | - |
| PoC Release Gap | - |
| Exploit DB References | None identified |
Affected Products & Versions
| Vendor | Product | Affected Versions |
|---|---|---|
| No affected products specified. | ||
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