Denial of Service via crafted Markdown input

Summary

Mistune is a Python Markdown parser with renderers and plugins. Prior to 3.3.0, Mistune is vulnerable to a CPU exhaustion DoS due to superlinear (approximately O(n²)) behavior in parse_link_text. When parsing Markdown containing many consecutive [ characters, parse_link_text repeatedly scans the input using a regex search inside a loop. Each iteration re-scans a large portion of the remaining string, resulting in quadratic-time behavior. An attacker-controlled Markdown input can therefore trigger excessive CPU usage with a very small payload. This vulnerability is fixed in 3.3.0. A flaw was found in Mistune, a Python Markdown parser. A remote attacker can exploit this vulnerability by providing a specially crafted Markdown input containing many consecutive bracket characters. This can lead to excessive CPU usage, causing a denial-of-service (DoS) condition on the affected system. Red Hat severity: Important — CVSS 7.5 (CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H). Weakness: CWE-1333. No fixing RHSA erratum has published yet; monitor the Red Hat CVE page and patch when it ships.