static bool smtp_endofresp(struct connectdata *conn, char *line, size_t len,
                           int *resp)
{
  struct smtp_conn *smtpc = &conn->proto.smtpc;
  bool result = FALSE;

  /* Nothing for us */
  if(len < 4 || !ISDIGIT(line[0]) || !ISDIGIT(line[1]) || !ISDIGIT(line[2]))
    return FALSE;

  /* Do we have a command response? This should be the response code followed
     by a space and optionally some text as per RFC-5321 and as outlined in
     Section 4. Examples of RFC-4954 but some e-mail servers ignore this and
     only send the response code instead as per Section 4.2. */
  if(line[3] == ' ' || len == 5) {
    result = TRUE;
    *resp = curlx_sltosi(strtol(line, NULL, 10));

    /* Make sure real server never sends internal value */
    if(*resp == 1)
      *resp = 0;
  }
  /* Do we have a multiline (continuation) response? */
  else if(line[3] == '-' &&
          (smtpc->state == SMTP_EHLO || smtpc->state == SMTP_COMMAND)) {
    result = TRUE;
    *resp = 1;  /* Internal response code */
  }

  return result;
}

The product performs operations on a memory buffer, but it reads from or writes to a memory location outside the buffer's intended boundary. This may result in read or write operations on unexpected memory locations that could be linked to other variables, data structures, or internal program data.