The OPC UA implementations (ANSI C and C++) as used in several SIMATIC products contain a denial of service vulnerability that could allow an unauthenticated remote attacker to create a denial of service condition by sending a specially crafted certificate.
Siemens has released updates for several affected products and recommends to update to the latest versions. Siemens is preparing further updates and recommends countermeasures for products where updates are not, or not yet available.

https://cert-portal.siemens.com/productcert/html/ssa-711309.html