CVE-2026-44899Mistune Image Directive CSS Injection Vulnerability
Updated under an hour ago ()
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No exploitation reported and no EPSS estimate yet.
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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.
- CVSS
- 4.7 MEDIUM (v3.1, CNA)CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:C/C:L/I:N/A:N
- Weakness (CWE)
- CWE-79
- Known exploited
- Not in CISA's KEV catalog
- EPSS (exploitation in the next 30 days)
- Not loaded for this CVE
- Assigned by
- GitHub_M
- NVD analysis
- Analyzed
- Record last updated
- May 27, 2026
- First seen by InfoSec Signals
- Oct 9, 2026
Affected products
lepture mistune lepture:mistune (from the name) | before 3.2.1 | CNA record |
mistune_project mistune mistune_project:mistune | before 3.2.1 | NVD |
References
- https://github.com/lepture/mistune/security/advisories/GHSA-ccfx-mfmx-2fx9x-refsource-confirm, exploit, vendor-advisory
- https://github.com/lepture/mistune/releases/tag/v3.2.1x-refsource-misc, product, release-notes
The CVE record on cve.org NVD's entry
The CVE record is authoritative. Products marked “from the name” were identified from the CNA's free-text names, not a CPE, and are matched less certainly. This product uses the NVD API but is not endorsed or certified by the NVD.