CVE-2026-59928: Mistune Project Mistune

High severity, CVSS 7.5. EPSS: 0.7% chance of exploitation in the next 30 days.

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.

Affected products

• Mistune Project Mistune: before 3.3.0 (fixed in 3.3.0)

Published 2026-07-08. Last modified 2026-07-09.