PyMdown Extensions is a set of extensions for the Python-Markdown markdown project. From 10.0.1 until 10.21.3, pymdownx.snippets uses a string-prefix containment check in SnippetPreprocessor.get_snippet_path() in pymdownx/snippets.py when `restrict_base_path: True`, allowing markdown snippet directives to read files from sibling paths that share the same base_path prefix, such as docs and docs_internal. This is a regression of CVE-2023-32309. This issue is fixed in version 10.21.3.
https://github.com/facelessuser/pymdown-extensions/security/advisories/GHSA-62q4-447f-wv8h
https://github.com/facelessuser/pymdown-extensions/releases/tag/10.21.3
https://github.com/facelessuser/pymdown-extensions/commit/63b7835776d703d6c339cf2110d9888f676efc0c