Bug 2481721 (CVE-2026-44899)

Summary: CVE-2026-44899 python-mistune: Mistune: Information disclosure via CSS injection in Image directive plugin
Product: [Other] Security Response Reporter: OSIDB Bzimport <bzimport>
Component: vulnerabilityAssignee: Product Security DevOps Team <prodsec-dev>
Status: NEW --- QA Contact:
Severity: medium Docs Contact:
Priority: medium    
Version: unspecifiedCC: anthomas, ehelms, ggainey, jkoehler, juwatts, lphiri, mhulan, nmoumoul, osousa, pcreech, rchan, rjohnson, smallamp, tmalecek
Target Milestone: ---Keywords: Security
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Hardware: All   
OS: Linux   
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A flaw was found in Mistune, a Python Markdown parser. The Image directive plugin, responsible for handling image dimensions, improperly validates user-supplied input for width and height options. This allows a remote attacker to inject arbitrary CSS into style attributes, potentially leading to information disclosure or other client-side attacks through Cross-site Scripting (XSS).
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Description OSIDB Bzimport 2026-05-26 22:01:56 UTC 
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.