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CVE-2026-61632 — PyMdown Extensions: Path traversal in the b64 extension lets read files outside base_path

Affected: facelessuser pymdown-extensions

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.

GHSA-9xwg-3r6f-jcx2 — PyMdown Extensions: Path traversal in the b64 extension lets read files outside base_path

Affected: PyPI: pymdown-extensions

### Summary

The `b64` extension inlines images referenced by `<img src="...">` as base64 data URIs. When resolving the `src` path it joins it onto the configured `base_path` with `os.path.normpath` and opens the result directly, with no check that the resolved path stays inside `base_path`. A `src` containing `../` sequences, or an absolute path, therefore reads a file outside `base_path` as long as that file has an allowed image extension (`.png`, `.jpg`, `.jpeg`, `.gif`, `.svg`). The base64 of that file is then embedded in the rendered output, disclosing its contents.

This is a separate code path from the `snippets` traversal issues (GHSA-jh85-wwv9-24hv, GHSA-62q4-447f-wv8h). It lives in `pymdownx/b64.py` and has no path restriction of any kind. Confirmed on `10.21.3` installed from PyPI.

### Details

In `pymdownx/b64.py`, function `repl_path` (around lines 68 to 90 on `main`):

```python if is_absolute: file_name = os.path.normpath(path) # absolute src: base_path ignored entirely else: file_name = os.path.normpath(os.path.join(base_path, path)) # relative src: '../' escapes base_path if os.path.exists(file_name): ext = os.path.splitext(file_name)[1].lower() for b64_ext in file_types: if ext in b64_ext: with open(file_name, "rb") as f: # opened with no containment check ... ```

There is no `startswith(base_path)`, no `os.path.realpath` comparison, and no rejection of `..`. B…

PYSEC-2026-3609 — PyMdown Extensions: Path traversal in the b64 extension lets read files outside base_path

Affected: PyPI: pymdown-extensions

### Summary

### Details

In `pymdownx/b64.py`, function `repl_path` (around lines 68 to 90 on `main`):

There is no `startswith(base_path)`, no `os.path.realpath` comparison, and no rejection of `..`. B…