An issue was discovered on Dasan GPON home routers. Command Injection can occur via the dest_host parameter in a diag_action=ping request to a GponForm/diag_Form URI. Because the router saves ping results in /tmp and transmits them to the user when the user revisits /diag.html, it's quite simple to execute commands and retrieve their output.
https://www.vpnmentor.com/blog/critical-vulnerability-gpon-router/