Multiple D-Link DIR-series routers, including DIR-110, DIR-412, DIR-600, DIR-610, DIR-615, DIR-645, and DIR-815 firmware version 1.03, contain a vulnerability in the service.cgi endpoint that allows remote attackers to execute arbitrary system commands without authentication. The flaw stems from improper input handling in the EVENT=CHECKFW parameter, which is passed directly to the system shell without sanitization. A crafted HTTP POST request can inject commands that are executed with root privileges, resulting in full device compromise. These router models are no longer supported at the time of assignment and affected version ranges may vary. Exploitation evidence was first observed by the Shadowserver Foundation on 2025-08-21 UTC.