SIPROTEC 5 devices contain a null pointer dereference vulnerability in the web service. This could allow an attacker to send unauthenticated maliciously crafted http request that could cause denial of service condition of the device.
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-322980.html