CVE-2026-44727

Summary

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 Software

Weaknesses

• CWE-79: CWE-79: Improper Neutralization of Input During Web Page Generation ('Cross-site Scripting')
• CWE-1021: CWE-1021: Improper Restriction of Rendered UI Layers or Frames

ADP Enrichment

CISA ADP Vulnrichment

• SSVC:
• Exploitation: none
  • Automatable: no
  • Technical Impact: total

jupyter-server: Jupyter Server: Remote Code Execution via stored Cross-Site Scripting in nbconvert handlers

Additional References

• 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

References

• https://github.com/jupyter-server/jupyter_server/security/advisories/GHSA-fcw5-x6j4-ccmp
• https://github.com/jupyter-server/jupyter_server/commit/6cbee8d65e71abac851c4492fea987ad080580bd

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