lepture mistune up to 3.2.x Python Markdown Parser resource consumption

Summaryinfo

A vulnerability labeled as problematic has been found in lepture mistune up to 3.2.x. Impacted is an unknown function of the component Python Markdown Parser. The manipulation results in resource consumption. This vulnerability was named CVE-2026-49851. The attack may be performed from remote. There is no available exploit. The affected component should be upgraded.

Detailsinfo

A vulnerability was found in lepture mistune up to 3.2.x. It has been classified as problematic. Affected is an unknown part of the component Python Markdown Parser. The manipulation with an unknown input leads to a resource consumption vulnerability. CWE is classifying the issue as CWE-400. The product does not properly control the allocation and maintenance of a limited resource, thereby enabling an actor to influence the amount of resources consumed, eventually leading to the exhaustion of available resources. This is going to have an impact on availability. CVE summarizes:

Mistune is a Python Markdown parser with renderers and plugins. Prior to 3.3.0, Mistune is vulnerable to a CPU exhaustion DoS due to superlinear (approximately O(n²)) behavior in parse_link_text. When parsing Markdown containing many consecutive [ characters, parse_link_text repeatedly scans the input using a regex search inside a loop. Each iteration re-scans a large portion of the remaining string, resulting in quadratic-time behavior. An attacker-controlled Markdown input can therefore trigger excessive CPU usage with a very small payload. This vulnerability is fixed in 3.3.0.

The advisory is shared for download at github.com. This vulnerability is traded as CVE-2026-49851 since 06/02/2026. The exploitability is told to be easy. It is possible to launch the attack remotely. The exploitation doesn't require any form of authentication. There are neither technical details nor an exploit publicly available. The MITRE ATT&CK project declares the attack technique as T1499.

Upgrading to version 3.3.0 eliminates this vulnerability.

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Productinfo

Vendor

• lepture

Name

• mistune

Version

• 3.0
• 3.1
• 3.2

Website

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

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