CVE-2026-44727

EUVD-2026-38347
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
ProviderTypeBase ScoreAtk. VectorAtk. ComplexityPriv. RequiredVector
NISTPrimary
5.4 MEDIUM
NETWORK
LOW
LOW
CVSS:3.1/AV:N/AC:L/PR:L/UI:R/S:C/C:L/I:L/A:N
Base Score
CVSS 3.x
EPSS Score
Percentile: 22.8%
Affected Products (NVD)
VendorProductVersion
jupyterjupyter_server
𝑥
< 2.20.0
𝑥
= Vulnerable software versions
Early Detection
Affected products identified ahead of NVD analysis through intelligence sources.
VendorProductVersionSource
Red HatRed Hat Migration Toolkit for Applications 8.2
1784109883 ≤
𝑥
< *
ADP
Debian logo
Debian Releases
Debian Product
Codename
jupyter-server
bookworm
postponed
bullseye
postponed
forky
2.20.0-3
fixed
sid
2.20.0-3
fixed
trixie
no-dsa
Ubuntu logo
Ubuntu Releases
Ubuntu Product
Codename
jupyter-server
jammy
needs-triage
noble
needs-triage
questing
ignored
resolute
needs-triage
Common Weakness Enumeration
References
https://github.com/jupyter-server/jupyter_server/commit/6cbee8d65e71abac851c4492fea987ad080580bd
https://github.com/jupyter-server/jupyter_server/security/advisories/GHSA-fcw5-x6j4-ccmp
https://access.redhat.com/errata/RHSA-2026:43038
https://access.redhat.com/security/cve/CVE-2026-44727
https://bugzilla.redhat.com/show_bug.cgi?id=2491516
https://security.access.redhat.com/data/csaf/v2/vex/2026/cve-2026-44727.json