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BREW-adr-viewer-CVE-2026-59924 — Mistune: Arbitrary File Read via Include directive path traversal

Affected: Homebrew: adr-viewer

### Summary

A path traversal issue exists in mistune's `Include` directive when markdown files are processed using `md.read()`. A crafted include path can cause files outside the intended markdown directory to be accessed.

### Details

The issue occurs in the `Include.parse()` method where user-supplied paths are joined and normalized without verifying that the resulting path remains within an expected directory.

```python relpath = self.parse_title(m) dest = os.path.join(os.path.dirname(source_file), relpath) dest = os.path.normpath(dest) ```

Because the final path is not restricted to a trusted base directory, path traversal sequences such as `../` may reference files outside the intended location.

### Proof of Concept

Create a markdown file:

```markdown .. include:: ../../../example.txt ```

Process it using:

```python import mistune from mistune.directives import RSTDirective, Include

md = mistune.create_markdown( plugins=[RSTDirective([Include()])] )

result, state = md.read("test.md") print(result) ```

### Impact

Applications that process untrusted markdown files with the `Include` directive enabled may allow unintended file access. The impact depends on how the feature is used and what files are accessible to the running process.

### Recommended Fix

Validate the resolved path and ensure it remains within an allowed directory before opening the file.

EUVD-2026-334035

fkie_cve-2026-59924

Mistune is a Python Markdown parser with renderers and plugins. Prior to 3.3.0, Include.parse() joins and normalizes user-supplied include paths without verifying that the result remains within the intended markdown directory, allowing crafted include paths to access files outside that directory when markdown files are processed using md.read(). This issue is fixed in version 3.3.0.

GHSA-r4rv-85jg-w4mf — Mistune: Arbitrary File Read via Include directive path traversal

Affected: PyPI: mistune