# CVE-2026-44727

## Summary

- **CVE ID:** CVE-2026-44727
- **Severity:** CRITICAL
- **CVSS Score:** 9.3 (CVSS:4.0/AV:N/AC:L/AT:N/PR:L/UI:A/VC:H/VI:H/VA:H/SC:H/SI:H/SA:H)
- **CWE:** CWE-79, CWE-1021
- **Published:** Jun 22, 2026
- **Last Modified:** Aug 28, 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.

## Affected Products

- jupyter-server — jupyter_server (< 2.20)

## References

- [CNA](https://github.com/jupyter-server/jupyter_server/security/advisories/GHSA-fcw5-x6j4-ccmp)
- [CNA](https://github.com/jupyter-server/jupyter_server/commit/6cbee8d65e71abac851c4492fea987ad080580bd)
- [redhat-SADP](https://access.redhat.com/security/cve/CVE-2026-44727)
- [redhat-SADP](https://bugzilla.redhat.com/show_bug.cgi?id=2491516)
- [redhat-SADP](https://security.access.redhat.com/data/csaf/v2/vex/2026/cve-2026-44727.json)
- [redhat-SADP](https://access.redhat.com/errata/RHSA-2026:43038)
- [redhat-SADP](https://access.redhat.com/errata/RHSA-2026:60520)

## Exploitation Prediction (EPSS)

- **EPSS Score:** 0.44%
- **EPSS Percentile:** 36.9

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_Exported from OnDuty AI Vulnerability Intelligence on 2026-09-10._