CVE-2026-44899: Mistune Project Mistune

Medium severity, CVSS 6.1. EPSS: 0.3% chance of exploitation in the next 30 days.

Mistune is a Python Markdown parser with renderers and plugins. Prior to 3.2.1, the Image directive plugin validates the :width: and :height: options with a regex compiled as _num_re = re.compile(r"^\d+(?:\.\d*)?"). When the validated value is not a plain integer, render_block_image() inserts it directly into a style="width:...;" or style="height:...;" attribute. Because the value was accepted by the prefix-only regex, any CSS after the leading digits reaches the style= attribute verbatim and without escaping. This vulnerability is fixed in 3.2.1.

Affected products

Published 2026-05-26. Last modified 2026-07-24.