# CVE-2026-59926: Mistune: XSS via unescaped class option in Admonition directive

CVE-2026-59926 is fixed in 2 products on 1 platform, first by DEBIAN-CVE-2026-59926, released July 8, 2026. It is not reported as exploited. Patch Radar priority: Routine.

- Web page: https://patchblox.com/security/cve/CVE-2026-59926
- Priority: Routine
- CVSS: 6.1 (Moderate)
- EPSS: 0.0033
- CISA KEV: not listed
- Exploited (vendor report): no
- Publicly disclosed: no
- Published: Jul 8, 2026
- Weakness: Improper Neutralization of Input During Web Page Generation ('Cross-site Scripting')
- Vendor advisory: https://msrc.microsoft.com/update-guide/vulnerability/CVE-2026-59926

## 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.

## Where it's fixed

| Platform | Product | Fixed in | Fix | Released |
|---|---|---|---|---|
| Linux | mistune Debian 14 | 3.1.4-1 | [DEBIAN-CVE-2026-59926](https://patchblox.com/security/data/fix/linux/debian-cve-2026-59926.md) | Jul 8, 2026 |
| Linux | python-mistune opensuse-leap 16.0 | 3.1.3-160000.5.1 | [OPENSUSE-SU-2026:21339-1](https://patchblox.com/security/data/fix/linux/opensuse-su-2026-21339-1.md) | Jul 14, 2026 |
| Linux | python-mistune sles 16.0 | 3.1.3-160000.5.1 | [SUSE-SU-2026:22655-1](https://patchblox.com/security/data/fix/linux/suse-su-2026-22655-1.md) | Jul 14, 2026 |

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Data as of 2026-11-09T01:18:40Z UTC. Source: Patchblox Patch Radar (https://patchblox.com/security/patch-radar). Patchblox finds out-of-date software on Windows, macOS and Linux and updates it through release rings: https://patchblox.com/demo

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