CVE-2026-59928 | Mistune is a Python Markdown parser with renderers and plugi… | CVSS 7.5 HIGH

Description

Mistune is a Python Markdown parser with renderers and plugins. Prior to 3.3.0, a Markdown document containing many repeated or distinct reference-link definitions causes quadratic work in src/mistune/block_parser.py and the ref_links environment dictionary handling, allowing denial of service through CPU exhaustion. This issue is fixed in version 3.3.0.

Metadata

CVE ID: CVE-2026-59928
State: PUBLISHED
Assigner: GitHub_M
Reserved: 2026-07-07 18:20 UTC
Published: 2026-07-08 16:23 UTC
Last updated: 2026-07-08 19:40 UTC
Primary CWE: CWE-407
CWE-407: Inefficient Algorithmic Complexity
Vendor / Product: lepture / mistune
Sources: cve.org · NVD

Severity & Metrics

7.5 HIGH CVSS 3.1

CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H

SSVC — CISA Coordinator

Exploitation: PoC
Automatable: yes
Tech. Impact: partial

Affected products (1)

Vendor	Product	Platform	Versions
lepture	mistune	—	< 3.3.0

Weakness (CWE)

CWE	Source	Description
CWE-1333	cna	CWE-1333: Inefficient Regular Expression Complexity
CWE-407	cna	CWE-407: Inefficient Algorithmic Complexity

CVSS scores (1)

Score	Severity	Version	Source	Vector
7.5	HIGH	3.1	cna	CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H

References (3)

https://github.com/lepture/mistune/security/advisories/GHSA-ffq3-xpv3-j92q https://github.com/lepture/mistune/security/advisories/GHSA-ffq3-xpv3-j92q
https://github.com/lepture/mistune/commit/2b04d7ba341c16ac78fe82d3076bdd5c3de87c69 https://github.com/lepture/mistune/commit/2b04d7ba341c16ac78fe82d3076bdd5c3de87c69
https://github.com/lepture/mistune/releases/tag/v3.3.0 https://github.com/lepture/mistune/releases/tag/v3.3.0