CVE-2026-61632: PyMdown Extensions: Path traversal in the b64 extension lets <img src> read files outside base_path

Vulnerability summary

CVE-2026-61632 is a medium (CVSS 5.3) vulnerability in facelessuser pymdown-extensions. EPSS estimates a 0.40% chance of exploitation in the next 30 days, higher than 34.6% of scored vulnerabilities.

Timeline

1. 06-08-2026
   PublishedVulnerability first disclosed.
2. 07-08-2026
   Last modifiedVulnerability information updated.

Description

PyMdown Extensions is a set of extensions for the Python-Markdown markdown project. In versions up to and including 10.21.3, the b64 extension is vulnerable to a path traversal that discloses arbitrary files: it inlines images referenced by <img src="..."> by joining the src onto the configured base_path with os.path.normpath and opening the result directly, without verifying that the resolved path stays inside base_path. As a result, an src containing ../ sequences or an absolute path reads a file outside base_path as long as it has an allowed image extension (.png, .jpg, .jpeg, .gif, .svg), and the file's contents are then base64-encoded into the rendered output, disclosing them. An application that renders untrusted Markdown with pymdownx.b64 enabled can therefore leak the contents of image-extension files readable by the process to whoever controls the Markdown or views the output, a targeted file-read bounded by the extension check. This issue has been fixed in version 11.0.

• CWE-22Improper Limitation of a Pathname to a Restricted DirectoryThe 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.