CVE-2026-59926: CWE-79: Improper Neutralization of Input During Web Page Generation ('Cross-site Scripting') in lepture mistune
Mistune is a Python Markdown parser with renderers and plugins. Prior to 3.2.1, render_admonition() in src/mistune/directives/admonition.py concatenates the Admonition directive :class: option into the HTML class attribute without escaping, allowing attribute injection and cross-site scripting even when HTMLRenderer escape mode is enabled. This issue is fixed in version 3.2.1.
AI Analysis
Technical Summary
CVE-2026-59926 is a CWE-79 (Improper Neutralization of Input During Web Page Generation) vulnerability in the lepture mistune project. Specifically, the render_admonition() function in src/mistune/directives/admonition.py improperly concatenates user-controlled input into the HTML class attribute without escaping. This flaw permits attribute injection and cross-site scripting attacks despite the HTMLRenderer escape mode being enabled. The vulnerability affects versions prior to 3.2.1 and is resolved in version 3.2.1.
Potential Impact
An attacker can exploit this vulnerability to inject malicious HTML attributes and execute cross-site scripting attacks. This can lead to the execution of arbitrary scripts in the context of the victim's browser, potentially resulting in session hijacking, defacement, or other client-side impacts. The CVSS 4.0 base score is 5.3, indicating a medium severity level.
Mitigation Recommendations
Upgrade to mistune version 3.2.1 or later, where this vulnerability is fixed. Since the fix is included in version 3.2.1, using this or a later version fully mitigates the issue. No other vendor advisory or patch information is available, so check the official mistune repository or vendor channels for the update.
CVE-2026-59926: CWE-79: Improper Neutralization of Input During Web Page Generation ('Cross-site Scripting') in lepture mistune
Description
Mistune is a Python Markdown parser with renderers and plugins. Prior to 3.2.1, render_admonition() in src/mistune/directives/admonition.py concatenates the Admonition directive :class: option into the HTML class attribute without escaping, allowing attribute injection and cross-site scripting even when HTMLRenderer escape mode is enabled. This issue is fixed in version 3.2.1.
CVSS v4.0
Score 5.3medium
Affected software
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Weaknesses
AI-Powered Analysis
Machine-generated threat intelligence
Technical Analysis
CVE-2026-59926 is a CWE-79 (Improper Neutralization of Input During Web Page Generation) vulnerability in the lepture mistune project. Specifically, the render_admonition() function in src/mistune/directives/admonition.py improperly concatenates user-controlled input into the HTML class attribute without escaping. This flaw permits attribute injection and cross-site scripting attacks despite the HTMLRenderer escape mode being enabled. The vulnerability affects versions prior to 3.2.1 and is resolved in version 3.2.1.
Potential Impact
An attacker can exploit this vulnerability to inject malicious HTML attributes and execute cross-site scripting attacks. This can lead to the execution of arbitrary scripts in the context of the victim's browser, potentially resulting in session hijacking, defacement, or other client-side impacts. The CVSS 4.0 base score is 5.3, indicating a medium severity level.
Mitigation Recommendations
Upgrade to mistune version 3.2.1 or later, where this vulnerability is fixed. Since the fix is included in version 3.2.1, using this or a later version fully mitigates the issue. No other vendor advisory or patch information is available, so check the official mistune repository or vendor channels for the update.
Technical Details
- Data Version
- 5.2
- Assigner Short Name
- GitHub_M
- Date Reserved
- 2026-07-07T18:20:06.126Z
- Cvss Version
- 4.0
- State
- PUBLISHED
- Remediation Level
- null
Threat ID: 6a4e7ad5c9d9e3dbe36a7df8
Added to database: 07/08/2026, 16:29:09 UTC
Last enriched: 07/08/2026, 16:43:47 UTC
Last updated: 08/22/2026, 14:02:33 UTC
Views: 81
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