Path Traversal in Jupyter Nbviewer
CVE-2026-86258
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.
Vulnerability class: Path Traversal (Directory Traversal)
Published · last modified .
CVSS v3 metric
CVSS v3 base score 5.9 (Medium). Vector: CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:H/I:N/A:N.
EPSS exploit prediction
EPSS: 0.005 (43.4th percentile), scored .
Very low probability of exploitation in the next 30 days; routine patching cadence is appropriate. 43rd percentile — 43.4% of CVEs in the catalogue have a lower EPSS than this one. How to read EPSS.
EPSS over last 30 days · oldest: 0.004 · newest: 0.005 · change: +0.002
Affected products
Weakness classification (CWE)
References
- GitHub Issue #1115 (issue-tracking)
- LocalFileHandler.can_show() at 1.0.1 (technical-description)
- Fix path-containment bypass in LocalFileHandler.can_show (PR #1116) (patch)
- github.com/jupyter/nbviewer (product)
- VulnCheck Advisory: nbviewer through 1.0.1 Path Traversal via LocalFileHandler (third-party-advisory)
Frequently asked questions
- What is CVE-2026-86258?
- CVE-2026-86258 is a medium-severity vulnerability in Jupyter Nbviewer, classified under Path Traversal. CVSS score: 5.9/10. Published 2026-09-06.
- How severe is CVE-2026-86258?
- Medium severity. CVSS v3 base score is 5.9 out of 10.