Introduction
CoinFabrik was asked to audit the contracts for the BankX project. First we will provide a summary of our discoveries, and then we will show the details of our findings.
Scope
The audited files are from the git repository located at https://github.com/Lance-Parker/BankX git repository, commit e99ff5f8cfe5697f2ddae7b1eb90cc3176659cf4, and in the https://github.com/Lance-Parker/CD git repository, commit 14a850049458348e6d4b1e8b2ce1e97ba678ca02.
The audited files are:
- BankX/contracts/BankX/BankXToken.sol: Staking token implementation
- BankX/contracts/BankX/BankX_premint.sol: Wrapper to BankXToken
- BankX/contracts/XSD/Pools/XSDWETHpool.sol: XSD/WETH pool
- BankX/contracts/XSD/Pools/BankXWETHpool.sol: BankX/WETH pool
- BankX/contracts/ERC20/ERC20Custom.sol: Modified ERC20 contract
- BankX/contracts/XSD/Pools/CollateralPool.sol: Collateral pool
- BankX/contracts/XSD/Pools/CollateralPoolLibrary.sol: Pool utility functions
- BankX/contracts/Uniswap/Router.sol: XSD/ETH/BankX Swap contract
- CD/contracts/interfaces/BankXInterface.sol: Interface to BankX Token
- CD/contracts/CD.sol: Certificate of Deposit main contract
- CD/contracts/GlobalsAndUtility.sol: Utility functions and global variables
- CD/contracts/StakeableToken.sol: Staking logic
The scope of the audit is limited to those files. No other files in this repository were audited. Its dependencies are assumed to work according to their documentation. Also, no tests were reviewed for this audit.
Analyses
Without being limited to them, the audit process included the following analyses:
- Arithmetic errors
- Outdated version of Solidity compiler
- Race conditions
- Reentrancy attacks
- Misuse of block timestamps
- Denial of service attacks
- Excessive gas usage
- Missing or misused function qualifiers
- Needlessly complex code and contract interactions
- Poor or nonexistent error handling
- Insufficient validation of the input parameters
- Incorrect handling of cryptographic signatures
- Centralization and upgradeability
Summary of Findings
We found a critical issue, a medium issue and a minor issue. Also, several enhancements were proposed.
Security Issues
| ID | Title | Severity | Status |
| CR-01 | Manipulation of Daily Payout | Critical | Acknowledged |
| ME-01 | Solidity Compiler Version | Medium | Resolved |
| MI-01 | Hardcoded Interest Rate And Launch Time | Minor | Resolved |
Security Issues Found
Severity Classification
Security risks are classified as follows:
- Critical: These are issues that we manage to exploit. They compromise the system seriously. They must be fixed immediately.
- Medium: These are potentially exploitable issues. Even though we did not manage to exploit them or their impact is not clear, they might represent a security risk in the near future. We suggest fixing them as soon as possible.
- Minor: These issues represent problems that are relatively small or difficult to take advantage of, but can be exploited in combination with other issues. These kinds of issues do not block deployments in production environments. They should be taken into account and be fixed when possible.
Issues Status
An issue detected by this audit can have four distinct statuses:
- Unresolved: The issue has not been resolved.
- Acknowledged: The issue remains in the code, but is a result of an intentional decision.
- Resolved: Adjusted program implementation to eliminate the risk.
- Partially resolved: Adjusted program implementation to eliminate part of the risk. The other part remains in the code, but is a result of an intentional decision.
- Mitigated: Implemented actions to minimize the impact or likelihood of the risk
Critical Severity Issues
CR-01 Manipulation of Daily Payout
Location:
- contracts/GlobalsAndUtility.sol:495 (CD)
The dailyDataUpdate() calculates the daily payout taking in account the BankX token total supply amount:
rs._allocSupplyCached = bankXContract.totalSupply() + g._lockedXsTotal;
And then at _dailyRoundCalc(), line 471:
rs._payoutTotal = rs._allocSupplyCached * 10000 / 171779836;
And then at _dailyRoundCalcAndStore(), line 483:
dailyData[day].dayPayoutTotal = uint72(rs._payoutTotal);
But the bankX supply can be manipulated by any authorized pool, In this way the daily payout can be manipulated, by increasing or decreasing the supply of BankX tokens and calling dailyDataUpdate() at appropriate times.
Recommendation
Restrict the dailyDataUpdate() function so the payout cannot be manipulated by an external entity.
Status
Acknowledged. According to the development team, this issue will be mitigated because after launch, admin keys will be renounced.
Medium Severity Issues
ME-01 Solidity Compiler Version
All the audited files use the statement:
pragma solidity 0.5.13;
This causes that very old solidity compiler version being used which may lead into hitting already fixed bugs. Normally this issue is of minor severity but due to the age of the solidity compiler specified (0.5.13) and the amount of bug fixes accumulated since that version, it was upgraded to Medium severity.
Recommendation
It is better to lock to a specific compiler version (for example, pragma solidity 0.8.13;) and keep it up to date, fully testing on each upgrade.
Status
Resolved.
Minor Severity Issues
MI-01 Hardcoded Interest Rate And Launch Time
Location:
- contracts/GlobalsAndUtility.sol:103,471 (CD)
The Launch date is hardcoded:
uint256 internal constant LAUNCH_TIME = 1575331200;
Also, the interest rate used to calculate the daily payout is a hard-coded constant:
rs._payoutTotal = rs._allocSupplyCached * 10000 / 171779836;
Recommendation
The LAUNCH_TIME constant could be a variable initialized at contract initialization. Also, a mechanism to update the interest rate should be implemented.
Status
Resolved.
Enhancements
These items do not represent a security risk. They are best practices that we suggest implementing.
Table
| ID | Title | Status |
| EN-01 | SafeMath Not Needed in Solidity >=0.8 | Implemented |
| EN-02 | Lack of Zero-Address Verification | Implemented |
| EN-03 | Different Reentrancy-Guard Methods | Implemented |
Details
EN-01 SafeMath not needed in Solidity >=0.8
Location:
- contracts/BankXToken.sol:2
- contracts/BankX_premint.sol:2
Solidity version 0.8 and over automatically reverts on integer overflows, not needing the SafeMath.sol contract anymore.
Recommendation
Remove the SafeMath.sol contract from the imports section and refactor the code appropriately.
Status
Implemented.
EN-02 Lack of zero-address Verification
Location:
- contracts/BankXWETHpool.sol:223
A zero-check on the new address should be added to the function setSmartContractOwner().
Status
Implemented.
EN-03 Different Reentrancy-Guard Methods
Location:
- contracts/CollateralPool.sol:69
CollateralPool.sol uses a custom lock, while XSDWETHpoo.sol and BankXWETHpool.sol uses OpenZepellins’s reentrancy guards, which is a better approach.
Recommendation
Replace custom guard code for OpenZepellins’s reentrancy guards.
Status
Implemented.
Other Considerations
Arbitrary Bonus Creation
Location:
- contracts/NFTBonus.sol:22 (CD)
Any user can get an arbitrarily big bonus by setting any number of OwnerIDs using NFTBonus.sol:setOwnerIds(). The function stackStartBonusXs() then will return an arbitrarily big bonus using this operation:
return bonusXs + bonusXs * nftBonusContract.getNftsCount(msg.sender) / 10;
Here, the getNftsCount(msg.sender) can return a multiplier controlled by the attacker, so bonusXs can be arbitrarily big. This is a critical bug as it allows stealing tokens from the contract but as this contract was out-of-scope for this audit, it was not added to the list of security issues, however it’s documented in this section.
Recommendation
Restrict the NFTBonus contract so only the owner can add or remove NFT ids.
Status
BankX responded that this was a test contract and because of that, it has no security impact.
Centralization
The contracts Pools/XSDWETHpool.sol, Pools/BankXWETHpool.sol and others use the Chainlink service as the price oracle.
Using an average or a backup Oracle solution might mitigate centralization, but are more costly, and security of a multi-oracle solution is not guaranteed.
Oracles are complex and approaches to decentralize come with security, accuracy and reliability tradeoffs. Chainlink oracles are powered by independent, professional and decentralized node operators that use multiple layers of aggregation – https://blog.chain.link/chainlink-price-feeds-secure-defi/
Upgrades
No upgrade mechanism exists in any contract audited.
Privileged Roles
These are the privileged roles that we identified on each of the audited contracts.
BankX/contracts/BankX/BankXToken.sol
Owner
The Owner can: Set the pool, set the Timelock address, set the Treasure address, set the XSD token address.
Timelock
The Timelock address can: Set the pool, set the Timelock address, set the Treasure address, set the XSD token address.
Pools
The XSD pools can: Mint new BankX tokens, burn BankX tokens.
BankX/contracts/BankX/BankX_premint.sol
Owner
The Owner can: Set the BankX token address, set the XSD token address.
BankX/contracts/XSD/Pools/BankXWETHpool.sol
Owner
The Owner can: Initialize the contract, change the owner address.
BankX/contracts/XSD/Pools/CollateralPool.sol
Owner
The Owner can: set the pool parameters, set the PID controller address.
BankX/contracts/Uniswap/Router.sol
Owner
The Owner can: Initialize the contract, change the owner address.
Treasury
The Treasury address can: Add new liquidity Tokens, add liquidity ETHs.
CD/contracts/GlobalsAndUtility.sol
Owner
The Owner can: Set the BankX contract address, set the NFTBonus contract address.
Changelog
- 2022-08-05 – Initial report based on commit e99ff5f8cfe5697f2ddae7b1eb90cc3176659cf4 for repository https://github.com/Lance-Parker/BankX and 14a850049458348e6d4b1e8b2ce1e97ba678ca02 for the repository https://github.com/Lance-Parker/CD.
- 2022-08-23 – Fixes checked on commit f127336bd6a8390c52fa6b2a93bde1306f529745 for repository https://github.com/Lance-Parker/BankX and E096bbce99cafb6e363b16dffec1ce3604c837d6 for repository https://github.com/Lance-Parker/CD.
