CVE-2026-86258: jupyter nbviewer Path Traversal

Vulnerability summary

CVE-2026-86258 is a high (CVSS 8.2) Path Traversal vulnerability in jupyter nbviewer. EPSS estimates a 0.52% chance of exploitation in the next 30 days, higher than 43.1% of scored vulnerabilities.

Timeline

1. 06-09-2026
   PublishedVulnerability first disclosed.
2. 24-09-2026
   Last modifiedVulnerability information updated.

Description

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.

• CWE-22Improper Limitation of a Pathname to a Restricted Directory ('Path Traversal')The product uses external input to construct a pathname that is intended to identify a file or directory that is located underneath a restricted parent directory, but the product does not properly neutralize special elements within the pathname that can cause the pathname to resolve to a location that is outside of the restricted directory.