Use of a hard-coded cryptographic key pair by the telnetd_startup service allows an attacker on the local area network to obtain a root she…

Use of a hard-coded cryptographic key pair by the telnetd_startup service allows an attacker on the local area network to obtain a root shell on the device over telnet. The builds of telnetd_startup included in the version 22.5.9.163 of the K2 firmware, and version 32.1.15.93 of the K3C firmware (possibly amongst many other releases) included both the private and public RSA keys. The remaining versions cited here redacted the private key, but left the public key unchanged. An attacker in possession of the leaked private key may, through a scripted exchange of UDP packets, instruct telnetd_startup to spawn an unauthenticated telnet shell as root, by means of which they can then obtain complete control of the device. A consequence of the limited availablility of firmware images for testing is that models and versions not listed here may share this vulnerability.