BIRD Internet Routing Daemon 1.6.x through 1.6.7 and 2.x through 2.0.5 has a stack-based buffer overflow. The BGP daemon's support for RFC 8203 administrative shutdown communication messages included an incorrect logical expression when checking the validity of an input message. Sending a shutdown communication with a sufficient message length causes a four-byte overflow to occur while processing the message, where two of the overflow bytes are attacker-controlled and two are fixed.