On the D-Link DIR-615 before v20.12PTb04, once authenticated, this device identifies the user based on the IP address of his machine. By spoofing the IP address belonging to the victim's host, an attacker might be able to take over the administrative session without being prompted for authentication credentials. An attacker can get the victim's and router's IP addresses by simply sniffing the network traffic. Moreover, if the victim has web access enabled on his router and is accessing the web interface from a different network that is behind the NAT/Proxy, an attacker can sniff the network traffic to know the public IP address of the victim's router and take over his session as he won't be prompted for credentials.
CWE-287 - Improper Authentication
Improper (or broken) authentication attacks are widespread, and have accounted for many of the worst data breaches in recent years. Improper authentication attacks are a class of vulnerabilities where an attacker impersonates a legitimate user by exploiting weaknesses in either session management or credential management to gain access to the user’s account. This can result in disclosure of sensitive information, and can lead to system compromise, theft, identity theft, and fraud.