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.
Exploitability
AV:NAC:LPR:NUI:RScope
S:CImpact
C:LI:NA:N4.7/CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:C/C:L/I:N/A:NInjection