Vulnerability Details CVE-2026-44898
Mistune is a Python Markdown parser with renderers and plugins. Prior to 3.2.1, render_toc_ul() builds a <ul> table-of-contents tree from a list of (level, id, text) tuples. Both the id value (used as href="#<id>") and the text value (used as the visible link label) are inserted into <a> tags via a plain Python format string — with no HTML escaping applied to either value. When heading IDs are derived from user-supplied heading text (the standard use-case for readable slug anchors), an attacker can craft a heading whose text breaks out of the href="#..." attribute context, injecting arbitrary HTML tags including <script> blocks directly into the rendered TOC. This vulnerability is fixed in 3.2.1.
Exploit prediction scoring system (EPSS) score
EPSS Score 0.0
EPSS Ranking 9.3%
CVSS Severity
CVSS v3 Score 6.1
References
Products affected by CVE-2026-44898
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cpe:2.3:a:mistune_project:mistune:0.1.0
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cpe:2.3:a:mistune_project:mistune:0.2.0
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cpe:2.3:a:mistune_project:mistune:0.3.0
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cpe:2.3:a:mistune_project:mistune:0.3.1
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cpe:2.3:a:mistune_project:mistune:0.4
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cpe:2.3:a:mistune_project:mistune:0.4.1
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cpe:2.3:a:mistune_project:mistune:0.5
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cpe:2.3:a:mistune_project:mistune:0.5.1
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cpe:2.3:a:mistune_project:mistune:0.6
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cpe:2.3:a:mistune_project:mistune:0.7
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cpe:2.3:a:mistune_project:mistune:0.7.1
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cpe:2.3:a:mistune_project:mistune:0.7.2
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cpe:2.3:a:mistune_project:mistune:0.7.3
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cpe:2.3:a:mistune_project:mistune:0.7.4
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cpe:2.3:a:mistune_project:mistune:0.8
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cpe:2.3:a:mistune_project:mistune:0.8.1
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cpe:2.3:a:mistune_project:mistune:0.8.2
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cpe:2.3:a:mistune_project:mistune:0.8.3
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cpe:2.3:a:mistune_project:mistune:0.8.4
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cpe:2.3:a:mistune_project:mistune:2.0.0
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cpe:2.3:a:mistune_project:mistune:2.0.1
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cpe:2.3:a:mistune_project:mistune:2.0.2
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cpe:2.3:a:mistune_project:mistune:2.0.3
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cpe:2.3:a:mistune_project:mistune:2.0.4
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cpe:2.3:a:mistune_project:mistune:2.0.5
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cpe:2.3:a:mistune_project:mistune:3.0.0
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cpe:2.3:a:mistune_project:mistune:3.0.1
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cpe:2.3:a:mistune_project:mistune:3.0.2
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cpe:2.3:a:mistune_project:mistune:3.1.0
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cpe:2.3:a:mistune_project:mistune:3.1.1
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cpe:2.3:a:mistune_project:mistune:3.1.2
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cpe:2.3:a:mistune_project:mistune:3.1.3
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cpe:2.3:a:mistune_project:mistune:3.1.4
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cpe:2.3:a:mistune_project:mistune:3.2.0