WAVLINK WN535M1 and WN535M3 routers running firmware prior to M35M1_V250922 contain an unauthenticated OS command injection vulnerability that allows remote attackers to execute arbitrary commands as root by sending crafted filenames to the sync_server daemon on TCP port 13136. The daemon interpolates attacker-controlled filename input containing shell metacharacters into a shell command string via sprintf() and passes it to system() without sanitization, enabling root-level command execution on the device.