A stack buffer overflow vulnerability exists in the D-Link DIR-816A2 router firmware DIR-816A2_FWv1.10CNB05_R1B011D88210.img in the upload.cgi module, which handles firmware version information. The vulnerability occurs because /proc/version is read into a 512-byte buffer and then concatenated using sprintf() into another 512-byte buffer containing a 29-byte constant. Input exceeding 481 bytes triggers a stack buffer overflow, allowing an attacker who can control /proc/version content to potentially execute arbitrary code on the device.