CVE-2026-44899

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 v3 4.7 MEDIUM

4.7^/10

CVSS v3 : MEDIUM

Vector :

Exploitability : 2.8 / Impact : 1.4

Attack Vector NETWORK

Attack Complexity LOW

Privileges Required NONE

User Interaction REQUIRED

Confidentiality Impact LOW

Integrity Impact NONE

Availability Impact NONE

Scope CHANGED

References

Link	Resource
https://github.com/lepture/mistune/releases/tag/v3.2.1	Product Release Notes
https://github.com/lepture/mistune/security/advisories/GHSA-ccfx-mfmx-2fx9	Exploit Vendor Advisory
https://github.com/lepture/mistune/security/advisories/GHSA-ccfx-mfmx-2fx9	Exploit Vendor Advisory

Configurations

Configuration 1 (hide)

cpe:2.3:a:mistune_project:mistune:*:*:*:*:*:*:*:*

History

No history.

Information

Published : 2026-05-26 21:16

Updated : 2026-07-24 11:10

NVD link : CVE-2026-44899

Mitre link : CVE-2026-44899

CVE.ORG link : CVE-2026-44899

JSON object : View

Products Affected

mistune_project

mistune

CWE

CWE-79

Improper Neutralization of Input During Web Page Generation ('Cross-site Scripting')

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