UBUNTU-CVE-2026-59926
Mistune, a Python Markdown parser, has a vulnerability in versions prior to 3.2.1 where the render_admonition() function improperly concatenates the Admonition directive :class: option into the HTML class attribute without escaping. This allows attribute injection and cross-site scripting (XSS) even when escape mode is enabled. The issue is fixed in version 3.2.1.
AI Analysis
Technical Summary
The vulnerability in Mistune affects the render_admonition() function in src/mistune/directives/admonition.py. It concatenates the :class: option from the Admonition directive directly into the HTML class attribute without proper escaping. This flaw enables attribute injection and cross-site scripting attacks despite the HTMLRenderer escape mode being enabled. The vulnerability is resolved in Mistune version 3.2.1.
Potential Impact
An attacker can exploit this vulnerability to perform attribute injection and cross-site scripting (XSS) attacks, potentially leading to the execution of malicious scripts in the context of users viewing rendered Markdown content. This can compromise user data confidentiality and integrity in affected environments.
Mitigation Recommendations
Upgrade Mistune to version 3.2.1 or later, where this vulnerability is fixed. No other mitigation is indicated by the vendor advisory.
UBUNTU-CVE-2026-59926
Description
Mistune, a Python Markdown parser, has a vulnerability in versions prior to 3.2.1 where the render_admonition() function improperly concatenates the Admonition directive :class: option into the HTML class attribute without escaping. This allows attribute injection and cross-site scripting (XSS) even when escape mode is enabled. The issue is fixed in version 3.2.1.
CVSS v4.0
Affected software
pkg:deb/ubuntu/[email protected]?arch=source&distro=bionicpkg:deb/ubuntu/[email protected]+really0.8.4-1?arch=source&distro=jammypkg:deb/ubuntu/[email protected]?arch=source&distro=questingpkg:deb/ubuntu/[email protected]?arch=source&distro=resoluteRun on your own infrastructure? Check whether these packages are installed with threat-finder — our free open-source scanner.
AI-Powered Analysis
Machine-generated threat intelligence
Technical Analysis
The vulnerability in Mistune affects the render_admonition() function in src/mistune/directives/admonition.py. It concatenates the :class: option from the Admonition directive directly into the HTML class attribute without proper escaping. This flaw enables attribute injection and cross-site scripting attacks despite the HTMLRenderer escape mode being enabled. The vulnerability is resolved in Mistune version 3.2.1.
Potential Impact
An attacker can exploit this vulnerability to perform attribute injection and cross-site scripting (XSS) attacks, potentially leading to the execution of malicious scripts in the context of users viewing rendered Markdown content. This can compromise user data confidentiality and integrity in affected environments.
Mitigation Recommendations
Upgrade Mistune to version 3.2.1 or later, where this vulnerability is fixed. No other mitigation is indicated by the vendor advisory.
Technical Details
- Gcve Source
- db.gcve.eu
- Osv Id
- UBUNTU-CVE-2026-59926
- Osv Schema Version
- 1.7.0
- Aliases
- []
- Ecosystems
- ["Ubuntu:16.04:LTS","Ubuntu:18.04:LTS","Ubuntu:20.04:LTS","Ubuntu:22.04:LTS","Ubuntu:24.04:LTS","Ubuntu:25.10","Ubuntu:26.04:LTS"]
- Database Specific Severity
- null
- Cvss Version
- 4.0
Threat ID: 6a58b44f68715ace43d6b6f7
Added to database: 07/16/2026, 10:37:03 UTC
Last enriched: 07/16/2026, 11:30:25 UTC
Last updated: 07/31/2026, 19:24:47 UTC
Views: 5
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