CVE-2026-5422: jupyter jupyter_server Relative Path Traversal

Vulnerability summary

CVE-2026-5422 is a high (CVSS 8.1) Relative Path Traversal vulnerability in jupyter jupyter_server. EPSS estimates a 0.55% chance of exploitation in the next 30 days, higher than 44.8% of scored vulnerabilities. 1 public exploit is recorded.

Timeline

1. 02-06-2026
   PublishedVulnerability first disclosed.
2. 02-06-2026
   Last modifiedVulnerability information updated.

Description

A path traversal vulnerability exists in jupyter-server version 2.17.0 due to an incorrect root directory boundary check in the _get_os_path() function within jupyter_server/services/contents/fileio.py. The check uses startswith(root) without appending a trailing path separator, allowing sibling directories with names starting with the same prefix as root_dir to bypass the check. Additionally, the to_os_path() function in utils.py does not strip ".." from path parts, enabling traversal sequences to bypass the vulnerable check. This vulnerability can lead to unauthorized read/write access to files in sibling directories, potentially exposing sensitive data in shared hosting environments.

• CWE-23Relative Path TraversalThe product uses external input to construct a pathname that should be within a restricted directory, but it does not properly neutralize sequences such as ".." that can resolve to a location that is outside of that directory.