In Mitsubishi Electric MELSEC-Q Series Q03/04/06/13/26UDVCPU: serial number 21081 and prior, Q04/06/13/26UDPVCPU: serial number 21081 and prior, and Q03UDECPU, Q04/06/10/13/20/26/50/100UDEHCPU: serial number 21081 and prior, MELSEC-L Series L02/06/26CPU, L26CPU-BT: serial number 21101 and prior, L02/06/26CPU-P, L26CPU-PBT: serial number 21101 and prior, and L02/06/26CPU-CM, L26CPU-BT-CM: serial number 21101 and prior, a remote attacker can cause the FTP service to enter a denial-of-service condition dependent on the timing at which a remote attacker connects to the FTP server on the above CPU modules.