An issue was discovered on TP-Link TL-WR840N v5 00000005 0.9.1 3.16 v0001.0 Build 170608 Rel.58696n and TL-WR841N v13 00000013 0.9.1 4.16 v0001.0 Build 170622 Rel.64334n devices. This issue is caused by improper session handling on the /cgi/ folder or a /cgi file. If an attacker sends a header of "Referer: http://192.168.0.1/mainFrame.htm" then no authentication is required for any action.

TP-Link TL-WR840N EU v6.20 was discovered to contain insecure protections for its UART console. This vulnerability allows attackers to connect to the UART port via a serial connection and execute commands as the root user without authentication.

TP-Link TL-WR840N v5 00000005 devices allow XSS via the network name. The attacker must log into the router by breaking the password and going to the admin login page by THC-HYDRA to get the network name. With an XSS payload, the network name changed automatically and the internet connection was disconnected. All the users become disconnected from the internet.