A command injection vulnerability exists in the D-Link DIR-823G router firmware DIR823G_V1.0.2B05_20181207.bin in the timelycheck and sysconf binaries, which process the /tmp/new_qos.rule configuration file. The vulnerability occurs because parsed fields from the configuration file are concatenated into command strings and executed via system() without any sanitization. An attacker with write access to /tmp/new_qos.rule can execute arbitrary commands on the device.