CVE-2026-44899 — Mistune Image Directive CSS Injection Vulnerability
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 _n…
Published: 2026-05-26 · CVSS: 4.7 · CVSS 3.1
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.
Source: CVE Program · Revision 8b16575c39f1e1810c5e863010da073d2d3285e7