CVE-2026-44899
Mistune Image Directive CSS Injection Vulnerability
- State
- Published
- Severity
- 4.7 Medium
- Published
- May 26, 2026
- Updated
- May 27, 2026
- Reserved
- May 7, 2026
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.
Scores
| CVSS | Score | Vector | Source |
|---|---|---|---|
| 3.1 | 4.7 Medium | CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:C/C:L/I:N/A:N | GitHub_M |
Weaknesses
- CWE-79 Improper Neutralization of Input During Web Page Generation ('Cross-site Scripting')
Affected Products
| Product | Versions |
|---|---|
mistunelepture |
|
References
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