CVE-2026-86258: Jupyter Nbviewer

Medium severity, CVSS 5.9. EPSS: 0.5% chance of exploitation in the next 30 days.

nbviewer through 1.0.1 contains a path traversal vulnerability in LocalFileHandler.can_show() that uses string-prefix comparison instead of proper path validation. Attackers can read files from sibling directories outside the configured root by requesting paths that share the root as a textual prefix, disclosing unintended notebooks and credentials.

Affected products

• Jupyter Nbviewer: up to and including 1.0.1

Published 2026-09-06. Last modified 2026-09-10.