The web interface of multiple D-Link routers, including DIR-600 rev B (≤2.14b01) and DIR-300 rev B (≤2.13), contains an unauthenticated OS command injection vulnerability in command.php, which improperly handles the cmd POST parameter. A remote attacker can exploit this flaw without authentication to spawn a Telnet service on a specified port, enabling persistent interactive shell access as root.

An OS command injection vulnerability exists in various legacy D-Link routers—including DIR-300 rev B and DIR-600 (firmware ≤ 2.13 and ≤ 2.14b01, respectively)—due to improper input handling in the unauthenticated command.php endpoint. By sending specially crafted POST requests, a remote attacker can execute arbitrary shell commands with root privileges, allowing full takeover of the device. This includes launching services such as Telnet, exfiltrating credentials, modifying system configuration, and disrupting availability. The flaw stems from the lack of authentication and inadequate sanitation of the cmd parameter.