Devices of the SIPROTEC 5 family contain a vulnerability related to secure client-initiated renegotiation. This could allow an unauthenticated attacker to cause a denial of service condition for the duration of the attack.
Siemens has released updates for several affected products and recommends to update to the latest versions. Siemens recommends specific countermeasures for products where updates are not, or not yet available.

https://cert-portal.siemens.com/productcert/html/ssa-552874.html