A vulnerability has been identified in SIMATIC S7-200 SMART CPU family (All versions >= V2.2 < V2.5.1). Affected devices do not properly handle large numbers of new incomming connections and could crash under certain circumstances. An attacker may leverage this to cause a Denial-of-Service situation.
https://cert-portal.siemens.com/productcert/pdf/ssa-589181.pdf