facelessuser PyMdown Extensions up to 10.21.3 b64 Extension pymdownx.b64 os.path.normpath src path traversal

Summaryinfo

A vulnerability classified as problematic was found in facelessuser PyMdown Extensions up to 10.21.3. Affected by this vulnerability is the function os.path.normpath of the file pymdownx.b64 of the component b64 Extension. Executing a manipulation of the argument src can lead to path traversal. This vulnerability appears as CVE-2026-61632. The attack may be performed from remote. There is no available exploit.

Detailsinfo

A vulnerability classified as problematic was found in facelessuser PyMdown Extensions up to 10.21.3. This vulnerability affects the function os.path.normpath of the file pymdownx.b64 of the component b64 Extension. The manipulation of the argument src with an unknown input leads to a path traversal vulnerability. The CWE definition for the vulnerability is CWE-22. The 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. As an impact it is known to affect confidentiality. CVE summarizes:

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.

The advisory is shared for download at github.com. This vulnerability was named CVE-2026-61632 since 07/10/2026. The exploitation appears to be easy. The attack can be initiated remotely. No form of authentication is required for a successful exploitation. Successful exploitation requires user interaction by the victim. There are known technical details, but no exploit is available. The MITRE ATT&CK project declares the attack technique as T1006.

Upgrading to version 11.0 eliminates this vulnerability.

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Productinfo

Vendor

• facelessuser

Name

• PyMdown Extensions

Version

• 10.21.0
• 10.21.1
• 10.21.2
• 10.21.3

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