French researcher discovered secret backdoor ‘TCP 32764’ discovered in several routers including, Linksys, Netgear, Cisco and Diamond that allowed an attacker to send commands to the vulnerable routers at TCP port 32764 from a command-line shell without being authenticated as the administrator. The flaw has been patched in the latest firmware release of Netgear DGN1000, but SerComm has added the same backdoor again in another way. An attacker can reactivate the TCP 32764 backdoor in order to execute the shell commands on the vulnerable SerComm routers even after installing the patched version.
Source: https://thehackernews.com/2014/04/router-manufacturers-secretly-added-tcp.html