Cattown is a JavaScript markdown parser. Versions prior to 1.0.2 used regular expressions with inefficient, potentially exponential worst-case complexity. This could cause excessive CPU usage due to excessive backtracking on crafted inputs. In turn, the excessive CPU usage could lead to resource exhaustion, where processing malicious inputs could cause high CPU or memory usage, potentially leading to denial of service. Version 1.0.2 contains a patch. Additionally, users should review and restrict input sources if untrusted inputs are processed.