Path Traversal in Jupyter Server Root Directory Validation

CVE-2026-5422 is a path traversal vulnerability affecting Jupyter Server 2.17.0 that allows attackers to access files outside the intended root directory. The flaw stems from two critical validation failures: the _get_os_path() function uses a simple startswith() check without enforcing strict path boundaries, and the to_os_path() function fails to sanitize ".." sequences from path components. This means an attacker can craft requests to sibling directories or traverse upward in the filesystem hierarchy, potentially exposing sensitive notebooks, configuration files, and other data. Jupyter Server deployments are particularly at risk in multi-user or cloud environments where sandboxing is critical to isolating user workspaces.

While this CVE maps to CWE-23 (Relative Path Traversal), it doesn't currently align with specific MITRE ATT&CK techniques in the standard framework, making traditional threat hunting difficult. However, Casky.ai's 754 mapped security skills enable detection of the underlying attack patterns through Claude's extended reasoning capabilities. Practitioners using Casky would identify suspicious behavior such as: unusual path resolution requests containing ".." sequences, access attempts to parent directories outside the notebook root, and anomalous file system queries that indicate directory escape attempts. By analyzing request patterns, file access logs, and path normalization failures, Casky helps security teams detect exploitation attempts before unauthorized file access occurs—critical for validating that their Jupyter deployments maintain proper isolation boundaries.