CVE-2026-59928 HIGH

CVE-2026-59928: Mistune block_parser: quadratic-time parsing on long lists of repeated reference-link definitions

Vendor Lepture
Product mistune
Weakness CWE-407
Published July 8, 2026
Last update July 8, 2026
View on NVD All CVEs

CVSS base score

7.5/10
Attack vector Network
Attack complexity Low
Privileges required None
User interaction None
Confidentiality None
Integrity None

CVSS vector

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

What the vulnerability does

01Description

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.

Key dates

02Disclosure timeline

July 8, 2026 CVE published
July 8, 2026 Record updated