I can't solve this Flawfinder Warning (CWE-78, CWE-120)

Question

I can't solve these two warnings found by Flawfinder. Could you answer to me with an example of the correct code?

Final results:

flawfinder_exercise_old_SAL_syntax.cpp:48:  [4] (shell) system:
  This causes a new program to execute and is difficult to use safely
  (CWE-78). try using a library call that implements the same functionality
  if available.<br>
flawfinder_exercise_old_SAL_syntax.cpp:36:  [2] (buffer) memcpy:
  Does not check for buffer overflows when copying to destination (CWE-120).
  Make sure destination can always hold the source data.*

This is the one in line 48:

int execute(char *buf) {
    return system(buf); // pass buf as command to be executed by the OS
}

---

This is the one in line 36:

void copy_data(char *buf1,
               char *buf2) {
    memcpy(buf2,buf1,STR_SIZE); 
    buf2[STR_SIZE-1] = NULL; // null terminate, just in case
}