The MELSEX iQ-R Series vulnerability allows an attacker to prevent legitimate clients from connecting to an affected product by manipulating the link parameter or changing its state. This is due to improper session management. However, if multiple MELSOFT transmission ports (TCP/IP) are open, the other ports are not affected. Sequence control is not affected by this vulnerability.
Refer to vendor advisory for the complete list of affected products and their respective patches at https://us-cert.cisa.gov/ics/advisories/icsa-21-147-05