buffer overflow on the read function that reads from the file to a buffer that is fixed size to 8000 bytes somthing like that , NX is enabled , so the stack is not executable
exploit : first to bypass the NX we need to call the API Virtualprotect to change the protection on the stack to executable then place our shellcode (to find the address of System in mscvrt.dll) after the return from VirtualProtect more explications on the script .