Mitsubishi MELSEC iQ-R Series PLCs with firmware 33 allow attackers to halt the industrial process by sending an unauthenticated crafted packet over the network, because this denial of service attack consumes excessive CPU time. After halting, physical access to the PLC is required in order to restore production.
https://www.us-cert.gov/ics/advisories/icsa-20-161-02
https://www.mitsubishielectric.com/en/psirt/vulnerability/pdf/2020-001_en.pdf