A stack buffer overflow vulnerability exists in the D-Link DIR-878A1 router firmware FW101B04.bin within the rc binary's USB storage handling module. The flaw arises from improper handling of the "Serial Number" field of a USB device, where sscanf copies data into a 64-byte buffer but fgets reads up to 127 bytes, causing a stack overflow. Exploitation requires physical access or control over a USB device and may allow arbitrary code execution on the device.