Describe CVE-2018-16557.
What is CVE-2018-16557?
A vulnerability has been identified in  SIMATIC S7-400 CPU 412-1 DP V7 (All versions),  SIMATIC S7-400 CPU 412-2 DP V7 (All versions),  SIMATIC S7-400 CPU 414-2 DP V7 (All versions),  SIMATIC S7-400 CPU 414-3 DP V7 (All versions),  SIMATIC S7-400 CPU 414-3 PN/DP V7 (All versions < V7.0.3),  SIMATIC S7-400 CPU 414F-3 PN/DP V7 (All versions < V7.0.3),  SIMATIC S7-400 CPU 416-2 DP V7 (All versions),  SIMATIC S7-400 CPU 416-3 DP V7 (All versions),  SIMATIC S7-400 CPU 416-3 PN/DP V7 (All versions < V7.0.3),  SIMATIC S7-400 CPU 416F-2 DP V7 (All versions),  SIMATIC S7-400 CPU 416F-3 PN/DP V7 (All versions < V7.0.3),  SIMATIC S7-400 CPU 417-4 DP V7 (All versions), SIMATIC S7-400 CPU 412-2 PN V7 (All versions < V7.0.3), SIMATIC S7-400 H V4.5 and below CPU family (incl. SIPLUS variants) (All versions), SIMATIC S7-400 H V6 CPU family (incl. SIPLUS variants) (All versions < V6.0.9), SIMATIC S7-400 PN/DP V6 and below CPU family (incl. SIPLUS variants) (All versions), SIMATIC S7-410 CPU family (incl. SIPLUS variants) (All versions < V8.2.1), SIPLUS S7-400 CPU 414-3 PN/DP V7 (All versions < V7.0.3), SIPLUS S7-400 CPU 416-3 PN/DP V7 (All versions < V7.0.3), SIPLUS S7-400 CPU 416-3 V7 (All versions), SIPLUS S7-400 CPU 417-4 V7 (All versions). Sending of specially crafted packets to port 102/tcp via Ethernet interface
via PROFIBUS or Multi Point Interfaces (MPI) could cause a denial of service
condition on affected devices. Flashing with a firmware image may be required
to recover the CPU.

Successful exploitation requires an attacker to have network access to port
102/tcp via Ethernet interface or to be able to send messages via PROFIBUS or
Multi Point Interfaces (MPI) to the device. No user interaction is required.
If no access protection is configured, no privileges are required to exploit
the security vulnerability. The vulnerability could allow causing a
denial of service condition of the core functionality of the CPU,
compromising the availability of the system..