Decimalchain - audit

In the contract `AccessControl` the role `ADMIN_ROLE` has authority over the functions: - revokeRole() - grantRole() Any compromise to the `ADMIN_ROLE` account may allow the hacker to take advantage of this authority. In the contract `DERC20` the role `ADMIN_ROLE` has authority over the functions shown in the diagram below. Any compromise to the `ADMIN_ROLE` account may allow the hacker to take advantage of this authority.  In the contract `DERC20` the role `BURNER_ROLE` has authority over the functions shown in the diagram below. Any compromise to the `BURNER_ROLE` account may allow the hacker to take advantage of this authority.  In the contract `DERC20` the role `MINTER_ROLE` has authority over the functions shown in the diagram below. Any compromise to the `MINTER_ROLE` account may allow the hacker to take advantage of this authority.  In the contract `DERC20` the role `PAUSER_ROLE` has authority over the functions shown in the diagram below. Any compromise to the `PAUSER_ROLE` account may allow the hacker to take advantage of this authority. 

In the contract DERC20, the role `MINTER_ROLE` has the authority to update the token balance of an arbitrary account without sanity restriction. Any compromise to the `MINTER_ROLE` account may allow a hacker to take advantage of this authority and manipulate users' balances. The hacker could also update his/her balance to a large number, sell these tokens, and cause the token price to drop.

The codebase contains multiple Solidity versions, which can lead to unexpected behavior, potential vulnerabilities, difficulties in maintaining the code, and inconsistencies in the execution of the smart contract. Using different versions may also result in increased complexity during code auditing, as different security features and bug fixes are present in different versions of the compiler. Versions used: `^0.8.0` `^0.8.0` is used in DERC20.sol file. ```solidity=702 pragma solidity ^0.8.0; ```