lepture mistune up to 3.2.0 Python Markdown Parser render_toc_ul ID cross site scripting

Summaryinfo

A vulnerability was found in lepture mistune up to 3.2.0. It has been classified as problematic. The affected element is the function render_toc_ul of the component Python Markdown Parser. Performing a manipulation of the argument ID results in cross site scripting. This vulnerability is identified as CVE-2026-44898. The attack can be initiated remotely. There is not any exploit available. Upgrading the affected component is recommended.

Detailsinfo

A vulnerability was found in lepture mistune up to 3.2.0. It has been classified as problematic. This affects the function render_toc_ul of the component Python Markdown Parser. The manipulation of the argument id with an unknown input leads to a cross site scripting vulnerability. CWE is classifying the issue as CWE-79. The product does not neutralize or incorrectly neutralizes user-controllable input before it is placed in output that is used as a web page that is served to other users. This is going to have an impact on integrity. The summary by CVE is:

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.

It is possible to read the advisory at github.com. This vulnerability is uniquely identified as CVE-2026-44898 since 05/07/2026. The exploitability is told to be easy. It is possible to initiate the attack remotely. No form of authentication is needed for exploitation. It demands that the victim is doing some kind of user interaction. Technical details of the vulnerability are known, but there is no available exploit. The attack technique deployed by this issue is T1059.007 according to MITRE ATT&CK.

The vulnerability scanner Nessus provides a plugin with the ID 321736 (Fedora 45 : python-mistune (2026-182b5d52c9)), which helps to determine the existence of the flaw in a target environment.

Upgrading to version 3.2.1 eliminates this vulnerability. The upgrade is hosted for download at github.com.

The vulnerability is also documented in the vulnerability database at Tenable (321736). Statistical analysis made it clear that VulDB provides the best quality for vulnerability data.

Productinfo

Vendor

• lepture

Name

• mistune

Version

• 3.0
• 3.1
• 3.2.0

Website

• Product: https://github.com/lepture/mistune/

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Statistical analysis made it clear that VulDB provides the best quality for vulnerability data.

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