A security vulnerability has been identified in DD-WRT, a popular custom firmware for Wi-Fi routers. The flaw is a buffer overflow weakness in the router's UPnP feature, a tool designed to let devices on your local network automatically connect and communicate with each other. An unauthenticated attacker, or someone with no prior permission to access your router, can exploit this issue to overflow an internal buffer used by UPnP, which can allow them to run unauthorized code on the router and take control of the device. If you use a DD-WRT router for the network that connects to your websites or related services hosted with us, a compromised router could create risk for those connected services.
Source: CISA Known Exploited Vulnerabilities Catalog — https://nvd.nist.gov/vuln/detail/CVE-2021-27137