Cubic catastrophic backtracking (ReDoS) in marked

Marked, a markdown parser, has a flaw in its pattern-matching code that can be exploited by sending specially crafted markdown text, causing the parser to freeze or consume excessive resources and becoming unavailable to other users.

The regular expression in the `block.def` pattern exhibits catastrophic backtracking (ReDoS) when processing certain malicious markdown input. An attacker can send crafted markdown strings to trigger exponential regex matching time, leading to denial of service. This affects any application parsing untrusted markdown with marked versions before 4.0.10 without resource limits or worker thread isolation.