CVE-2026-86430
league/commonmark versions before 2.9.1 contain multiple denial of service vulnerabilities in fenced code block detection, reference link label lookup, and emphasis delimiter processing that perform super-linear work on crafted input. Attackers can submit specially crafted Markdown with long backtick runs, nested brackets, or delimiter sequences to consume disproportionate CPU time and prevent legitimate requests from completing.
- Published Sep 7, 2026
- CVSS 8.7 high
- 0.5% chance of exploitation in the next 30 days (EPSS)
- A fix is available