A stack buffer overflow vulnerability exists in the D-Link DIR-878A1 router firmware FW101B04.bin in the rc binary's USB storage handling module. The vulnerability occurs when the "Serial Number" field from a USB device is read via sscanf into a 64-byte stack buffer, while fgets reads up to 127 bytes, causing a stack overflow. An attacker with physical access or control over a USB device can exploit this vulnerability to potentially execute arbitrary code on the device.