CVE-2026-33079: Mistune has a ReDoS in LINK_TITLE_RE that allows denial of service via crafted Markdown input

A ReDoS (Regular Expression Denial of Service) vulnerability in LINK_TITLE_RE allows an attacker who can supply Markdown for parsing to cause denial of service. A crafted 58-byte Markdown document blocks the parser for approximately 6 seconds (measured on Apple M2, Python 3.14.3), with exponential growth per additional byte pair.