CVE-2026-59928

Mistune (Python Markdown parser) prior to version 3.3.0 is vulnerable to a denial of service due to quadratic work in the block_parser.py processing of long references and in the ref_links environment dictionary. The issue arises when a Markdown document contains many repeated or distinct referen...

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

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/blockparser.py and the reflinks environment dictionary handling, allowing denial of service...