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Advanced Manual
Smart Contract Audit

August 16, 2022

Audit requested by

MVCC Token

0x80fB0Ff63B89CcdAEd3f6198aD86898845681C89

MVCC Token / Security Audit

Table of Contents

1. Audit Summary

1.1 Audit scope

1.2 Tokenomics

1.3 Source Code

2. Disclaimer

3. Global Overview

3.1 Informational issues

3.2 Low-risk issues

3.3 Medium-risk issues

3.4 High-risk issues

4. Vulnerabilities Findings

5. Contract Privileges

5.1 Maximum Fee Limit Check

5.2 Contract Pausability Check

5.3 Max Transaction Amount Check

5.4 Exclude From Fees Check

5.5 Ability to Mint Check

5.6 Ability to Blacklist Check

5.7 Owner Privileges Check

6. Notes

6.1 Notes by Coinsult

6.2 Notes by MVCC Token

7. Contract Snapshot

8. Website Review

9. Certificate of Proof

MVCC Token / Security Audit

Audit Summary

Audit Scope

Project Name

MVCC Token

Blockchain

Binance Smart Chain

Smart Contract Language

Solidity

Contract Address

0x80fB0Ff63B89CcdAEd3f6198aD86898845681C89

Audit Method

Static Analysis, Manual Review

Date of Audit

16 August 2022

This audit report has been prepared by Coinsult’s experts at the request of the client. In this audit, the results of the static analysis and the manual code review will be presented. The purpose of the audit is to see if the functions work as intended, and to identify potential security issues within the smart contract.

The information in this report should be used to understand the risks associated with the smart contract. This report can be used as a guide for the development team on how the contract could possibly be improved by remediating the issues that were identified.

MVCC Token / Security Audit

Tokenomics

Rank Address Quantity (Token) Percentage
1 0x1c13a1a23094c4cb1c92df2fa8f6651d60660266 10,000,000 100.0000%

Source Code

Coinsult was comissioned by MVCC Token to perform an audit based on the following code:
https://bscscan.com/address/0x80fB0Ff63B89CcdAEd3f6198aD86898845681C89#code

MVCC Token / Security Audit

Disclaimer

This audit report has been prepared by Coinsult’s experts at the request of the client. In this audit, the results of the static analysis and the manual code review will be presented. The purpose of the audit is to see if the functions work as intended, and to identify potential security issues within the smart contract.

The information in this report should be used to understand the risks associated with the smart contract. This report can be used as a guide for the development team on how the contract could possibly be improved by remediating the issues that were identified.

Coinsult is not responsible if a project turns out to be a scam, rug-pull or honeypot. We only provide a detailed analysis for your own research.

Coinsult is not responsible for any financial losses. Nothing in this contract audit is financial advice, please do your own research.

The information provided in this audit is for informational purposes only and should not be considered investment advice. Coinsult does not endorse, recommend, support or suggest to invest in any project. 

Coinsult can not be held responsible for when a project turns out to be a rug-pull, honeypot or scam.

MVCC Token / Security Audit

Global Overview

Manual Code Review

In this audit report we will highlight the following issues:

Vulnerability Level

Total

Pending

Acknowledged

Resolved

0

0

0

0

5

0

0

0

0

0

0

0

0

0

0

0

Privilege Overview

Coinsult checked the following privileges:

Contract Privilege

Description

Owner can mint?

Owner can blacklist?

Owner can set fees > 25%?

Owner can exclude from fees?

Owner can pause trading?

Owner can set Max TX amount?

More owner priviliges are listed later in the report.

MVCC Token / Security Audit

Contract contains Reentrancy vulnerabilities

Additional information: This combination increases risk of malicious intent. While it may be justified by some complex mechanics (e.g. rebase, reflections, buyback). 

More information: Slither

				
					    function _transfer(
        address from,
        address to,
        uint256 amount
    ) internal {
        require(from != address(0), "BEP20: transfer from the zero address");
        require(to != address(0), "BEP20: transfer to the zero address");
        require(amount > 0, "Transfer amount must be greater than zero");

        uint256 contractTokenBalance = balanceOf(address(this));
        
        bool isOverMinTokenBalance = contractTokenBalance >= swapThreshold;
        if (
            isOverMinTokenBalance &&
            !_inSwapAndLiquify &&
            !_isExcludedFromAutoLiquidity[from] &&
            _swapAndLiquifyEnabled
        ) {
            swapAndLiquify(contractTokenBalance);
        }

        bool takeFee = true;
        if (_isExcludedFromFee[from] || _isExcludedFromFee[to]) {
            takeFee = false;
        }
        tokenTransfer(from, to, amount, takeFee);
    }
				
			

Recommendation

Apply the check-effects-interactions pattern.

Exploit scenario

				
					    function withdrawBalance(){
        // send userBalance[msg.sender] Ether to msg.sender
        // if mgs.sender is a contract, it will call its fallback function
        if( ! (msg.sender.call.value(userBalance[msg.sender])() ) ){
            throw;
        }
        userBalance[msg.sender] = 0;
    }
				
			
Bob uses the re-entrancy bug to call withdrawBalance two times, and withdraw more than its initial deposit to the contract.

MVCC Token / Security Audit

Too many digits

Literals with many digits are difficult to read and review.

				
					    uint256 private constant _tTotal = 10000000 * 10**18;
				
			

Recommendation

Exploit scenario

				
					contract MyContract{
    uint 1_ether = 10000000000000000000; 
}
				
			

While 1_ether looks like 1 ether, it is 10 ether. As a result, it’s likely to be used incorrectly.

MVCC Token / Security Audit

No zero address validation for some functions

Detect missing zero address validation.

				
					    function setReferralFeeReceiver(address newReferralFeeReceiver) external onlyOwner {
        require(newReferralFeeReceiver != address(0), "Address zero");
        referralFeeReceiver = newReferralFeeReceiver;

        emit SetReferralFeeReceiver(newReferralFeeReceiver);
    }

    function setSuperNodeFeeReceiver(address newSuperNodeFeeReceiver) external onlyOwner {
        require(newSuperNodeFeeReceiver != address(0), "Address zero");
        superNodeFeeReceiver = newSuperNodeFeeReceiver;

        emit SetSuperNodeFeeReceiver(newSuperNodeFeeReceiver);
    }
				
			

Recommendation

Check that the new address is not zero.

Exploit scenario

				
					contract C {

  modifier onlyAdmin {
    if (msg.sender != owner) throw;
    _;
  }

  function updateOwner(address newOwner) onlyAdmin external {
    owner = newOwner;
  }
}
				
			

Bob calls updateOwner without specifying the newOwner, soBob loses ownership of the contract.

MVCC Token / Security Audit

Unchecked transfer

The return value of an external transfer/transferFrom call is not checked.

				
					    function rescueToken(address tokenAddress, address to) external onlyOwner {
        uint256 contractBalance = IERC20(tokenAddress).balanceOf(address(this));
        IERC20(tokenAddress).transfer(to, contractBalance);
    }
				
			

Recommendation

Use SafeERC20, or ensure that the transfer/transferFrom return value is checked.

Exploit scenario

				
					contract Token {
    function transferFrom(address _from, address _to, uint256 _value) public returns (bool success);
}
contract MyBank{  
    mapping(address => uint) balances;
    Token token;
    function deposit(uint amount) public{
        token.transferFrom(msg.sender, address(this), amount);
        balances[msg.sender] += amount;
    }
}
				
			

Several tokens do not revert in case of failure and return false. If one of these tokens is used in MyBankdeposit will not revert if the transfer fails, and an attacker can call deposit for free..

MVCC Token / Security Audit

Costly operations inside a loop

Costly operations inside a loop might waste gas, so optimizations are justified. 

				
					    function setIncludeInReward(address account) external onlyOwner {
        require(account != address(0), "Address zero");
        require(_isExcluded[account], "Account is not excluded");

        for (uint256 i = 0; i < _excluded.length; i++) {
            if (_excluded[i] == account) {
                _excluded[i] = _excluded[_excluded.length - 1];
                _tOwned[account] = 0;
                _isExcluded[account] = false;
                _excluded.pop();
                break;
            }
        }

        emit SetIncludeInReward(account);
    }
				
			

Recommendation

Use a local variable to hold the loop computation result.

Exploit scenario

				
					contract CostlyOperationsInLoop{

    function bad() external{
        for (uint i=0; i < loop_count; i++){
            state_variable++;
        }
    }

    function good() external{
      uint local_variable = state_variable;
      for (uint i=0; i < loop_count; i++){
        local_variable++;
      }
      state_variable = local_variable;
    }
}
				
			

Incrementing state_variable in a loop incurs a lot of gas because of expensive SSTOREs, which might lead to an out-of-gas.

MVCC Token / Security Audit

Contract Privileges

Maximum Fee Limit Check

Coinsult tests if the owner of the smart contract can set the transfer, buy or sell fee to 25% or more. It is bad practice to set the fees to 25% or more, because owners can prevent healthy trading or even stop trading when the fees are set too high. 

Type of fee

Description

Transfer fee

Buy fee

Sell fee

Type of fee

Description

Max transfer fee

Max buy fee

Max sell fee

MVCC Token / Security Audit

Contract Pausability Check

Coinsult tests if the owner of the smart contract has the ability to pause the contract. If this is the case, users can no longer interact with the smart contract; users can no longer trade the token.

Privilege Check

Description

Can owner pause the contract?

MVCC Token / Security Audit

Max Transaction Amount Check

Coinsult tests if the owner of the smart contract can set the maximum amount of a transaction. If the transaction exceeds this limit, the transaction will revert. Owners could prevent normal transactions to take place if they abuse this function.

Privilege Check

Description

Can owner set max tx amount?

MVCC Token / Security Audit

Exclude From Fees Check

Coinsult tests if the owner of the smart contract can exclude addresses from paying tax fees. If the owner of the smart contract can exclude from fees, they could set high tax fees and exclude themselves from fees and benefit from 0% trading fees. However, some smart contracts require this function to exclude routers, dex, cex or other contracts / wallets from fees.

Privilege Check

Description

Can owner exclude from fees?

MVCC Token / Security Audit

Ability To Mint Check

Coinsult tests if the owner of the smart contract can mint new tokens. If the contract contains a mint function, we refer to the token’s total supply as non-fixed, allowing the token owner to “mint” more tokens whenever they want.

A mint function in the smart contract allows minting tokens at a later stage. A method to disable minting can also be added to stop the minting process irreversibly.

Minting tokens is done by sending a transaction that creates new tokens inside of the token smart contract. With the help of the smart contract function, an unlimited number of tokens can be created without spending additional energy or money.

Privilege Check

Description

Can owner mint?

MVCC Token / Security Audit

Ability To Blacklist Check

Coinsult tests if the owner of the smart contract can blacklist accounts from interacting with the smart contract. Blacklisting methods allow the contract owner to enter wallet addresses which are not allowed to interact with the smart contract. 

This method can be abused by token owners to prevent certain / all holders from trading the token. However, blacklists might be good for tokens that want to rule out certain addresses from interacting with a smart contract.

Privilege Check

Description

Can owner blacklist?

MVCC Token / Security Audit

Other Owner Privileges Check

Coinsult lists all important contract methods which the owner can interact with.

⚠ Owner can change uniswap router

 

MVCC Token / Security Audit

Notes

Notes by MVCC Token

No notes provided by the team.

Notes by Coinsult

✅ No notes provided by Coinsult

MVCC Token / Security Audit

Contract Snapshot

This is how the constructor of the contract looked at the time of auditing the smart contract.

				
					contract MVCC is Context, IERC20, Ownable {
    string private constant _name = "MVCC TOKEN";
    string private constant _symbol = "MVCC";
    uint8 private constant _decimals = 18;

    uint256 private constant MAX = ~uint256(0);
    uint256 private constant _tTotal = 10000000 * 10**18;
    uint256 private _rTotal = (MAX - (MAX % _tTotal));
    uint256 private _tFeeTotal;

    address[] private _excluded;
    address public referralFeeReceiver;
    address public superNodeFeeReceiver;

    uint256 public referralFee = 5; 
    uint256 public superNodeFee = 2; 
    uint256 public liquidityFee = 2;  
    uint256 public taxFee = 1; // reflection
    uint256 public swapThreshold = _tTotal * 1/1000; //0.1%;
    
    // auto liquidity
    bool public _swapAndLiquifyEnabled = true;
    bool _inSwapAndLiquify;

    IPancakeRouter02 public _pancakeRouter;
    address public _pancakePair;

    mapping (address =&gt; uint256) private _rOwned;
    mapping (address =&gt; uint256) private _tOwned;
    mapping (address =&gt; bool) private _isExcludedFromFee;
    mapping (address =&gt; bool) private _isExcluded;
    mapping (address =&gt; mapping (address =&gt; uint256)) private _allowances;
    mapping (address =&gt; bool) public _isExcludedFromAutoLiquidity;

    modifier lockTheSwap {
        _inSwapAndLiquify = true;
        _;
        _inSwapAndLiquify = false;
    }
    
    constructor (address _referralFeeReceiver, address _superNodeFeeReceiver) {
        _rOwned[_msgSender()] = _rTotal;
				
			

MVCC Token / Security Audit

Website Review

Coinsult checks the website completely manually and looks for visual, technical and textual errors. We also look at the security, speed and accessibility of the website. In short, a complete check to see if the website meets the current standard of the web development industry. 

Type of check

Description

Mobile friendly?

Contains jQuery errors?

Is SSL secured?

Contains spelling errors?

MVCC Token / Security Audit

Certificate of Proof

MVCC Token

Audited by Coinsult.net

Date: 16 August 2022

Coinsult

coinsult.net

End of report
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