A vulnerability in MikroTik Version 6.41.4 could allow an unauthenticated remote attacker to exhaust all available CPU and all available RAM by sending a crafted FTP request on port 21 that begins with many '\0' characters, preventing the affected router from accepting new FTP connections. The router will reboot after 10 minutes, logging a "router was rebooted without proper shutdown" message.
https://www.exploit-db.com/exploits/44450/
http://packetstormsecurity.com/files/147183/MikroTik-6.41.4-Denial-Of-Service.html