CVE-2026-447279.0CriticalCWE-79

CVE-2026-44727: Jupyter Server: Stored XSS in `NbconvertFileHandler` / `NbconvertPostHandler` via missing `sandbox` CSP

jupyter-server · jupyter_server

Vendor fix available · Affected: jupyter-server jupyter_server · Exploitation: unlikely (under 1%)

Not in CyberSIXT coverage yet: no article names this CVE. This page shows the public record.

0.4%probability of exploitation in the next 30 days

38th percentile

050100

Higher than 38% of scored CVEs

9.0CriticalCVSS 3.1

LowMediumHighCrit.

DescriptionCVE.org

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 products1

From the CVE record. A product or version that is not listed is unknown, not unaffected.

jupyter-server · jupyter_server< 2.20

On the Atlas

Every published CVE is on the CyberSIXT Atlas, grouped by weakness, vendor and month.

Open the Atlas

Exploitation: Unlikely (under 1%). EPSS under 1%, or no score yet.
CISA KEV: Not listed
Public check: No public nuclei template
Weakness: Cross-site Scripting
Vendor: jupyter-server
Published: June 2026
Band: Unlikely (under 1%), June 2026

CoverageNo articles yet

No CyberSIXT article names CVE-2026-44727 yet, so there is no coverage timeline, action brief or change log for it. Everything on this page comes from the public CVE record, CISA KEV, EPSS and the nuclei template index. Search the archive or see the CVEs in the news.