CVE-2026-44899

Summary

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.

Affected Software

Weaknesses

• CWE-79: CWE-79: Improper Neutralization of Input During Web Page Generation ('Cross-site Scripting')

ADP Enrichment

CISA ADP Vulnrichment

• SSVC:
• Exploitation: poc
  • Automatable: no
  • Technical Impact: partial

Additional References

• https://github.com/lepture/mistune/security/advisories/GHSA-ccfx-mfmx-2fx9

References

• https://github.com/lepture/mistune/security/advisories/GHSA-ccfx-mfmx-2fx9
• https://github.com/lepture/mistune/releases/tag/v3.2.1

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