CVE-2026-44899
Medium
Description
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.
SeverityMedium
CVSS4.7
Exploit probability—
ProductMistune
PublishedMay 26, 2026
First seenMay 26, 2026
Weakness typeCWE-79Cross-site scripting (XSS)
How to fix
Update
- mistune_project mistune3.2.1 or later
- mistune3.2.1 or later
Affected products
| Product | Affected versions | Fixed in |
|---|---|---|
| mistune_project mistune | v < 3.2.1 | 3.2.1 |
| mistunePyPI | 3.2.0 ≤ v < 3.2.1, v < 3.2.1 | 3.2.1 |
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