The pymdown-extensions library for Python Markdown includes four inline processors (caret, tilde, betterem, and magiclink) that use regular expressions with content groups capable of partitioning delimiter runs in exponentially many ways. This inefficiency causes catastrophic backtracking, resulting in unbounded CPU consumption when processing a single crafted Markdown line under 50 bytes. An unauthenticated remote attacker able to submit Markdown can exploit this to cause denial of service in applications rendering untrusted Markdown, such as web comments, wikis, issue trackers, and documentation systems. The vulnerability affects versions up to and including 11.0 and has been fixed in version 11.0.1.

An attacker who can submit Markdown content to a vulnerable application can cause the rendering process to consume excessive CPU resources, leading to denial of service. This impacts availability but does not affect confidentiality or integrity. The vulnerability is relevant for any application using pymdown-extensions to render untrusted Markdown input.

Upgrade pymdown-extensions to version 11.0.1 or later, where this issue is fixed. No other mitigation or workaround is indicated in the available data.