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Security Audit
June 10th, 2024
Version 1.0.0
Presented by 0xMacro
This document includes the results of the security audit for Shroom's smart contract code as found in the section titled ‘Source Code’. The security audit was performed by the Macro security team on June 8, 2024.
The purpose of this audit is to review the source code of certain Shroom Solidity contracts, and provide feedback on the design, architecture, and quality of the source code with an emphasis on validating the correctness and security of the software in its entirety.
Disclaimer: While Macro’s review is comprehensive and has surfaced some changes that should be made to the source code, this audit should not solely be relied upon for security, as no single audit is guaranteed to catch all possible bugs.
The following is an aggregation of issues found by the Macro Audit team:
| Severity | Count | Acknowledged | Won't Do | Addressed |
|---|---|---|---|---|
| High | 1 | 1 | - | - |
| Code Quality | 2 | 2 | - | - |
| Informational | 1 | - | - | - |
Shroom was quick to respond to these issues.
Our understanding of the specification was based on the following sources:
The following source code was reviewed during the audit:
No repository
Specifically, we audited the smart contract deployed to the following address in the Polygon network: 0xf3abaa9ea255d38763a5d0ae6286d6df53154ddc
| Contract | SHA256 |
|---|---|
| ./src/CommunityCurrency.sol |
|
Note: This document contains an audit solely of the Solidity contracts listed above. Specifically, the audit pertains only to the contracts themselves, and does not pertain to any other programs or scripts, including deployment scripts.
Click on an issue to jump to it, or scroll down to see them all.
We quantify issues in three parts:
This third part – the severity level – is a summary of how much consideration the client should give to fixing the issue. We assign severity according to the table of guidelines below:
| Severity | Description |
|---|---|
|
(C-x) Critical |
We recommend the client must fix the issue, no matter what, because not fixing would mean significant funds/assets WILL be lost. |
|
(H-x) High |
We recommend the client must address the issue, no matter what, because not fixing would be very bad, or some funds/assets will be lost, or the code’s behavior is against the provided spec. |
|
(M-x) Medium |
We recommend the client to seriously consider fixing the issue, as the implications of not fixing the issue are severe enough to impact the project significantly, albiet not in an existential manner. |
|
(L-x) Low |
The risk is small, unlikely, or may not relevant to the project in a meaningful way. Whether or not the project wants to develop a fix is up to the goals and needs of the project. |
|
(Q-x) Code Quality |
The issue identified does not pose any obvious risk, but fixing could improve overall code quality, on-chain composability, developer ergonomics, or even certain aspects of protocol design. |
|
(I-x) Informational |
Warnings and things to keep in mind when operating the protocol. No immediate action required. |
|
(G-x) Gas Optimizations |
The presented optimization suggestion would save an amount of gas significant enough, in our opinion, to be worth the development cost of implementing it. |
transferFrom() charges double fee
The CommunityCurrency contract is mainly a standard ERC20 implementation, specifically inherited from Thirdweb’s ERC20 base. It uses some minimal custom logic to calculate, deduct, and transfer protocol fees, which are currently set at a fixed rate of 0,5% (taxRate set to 50 out of 10_000 max basis points).
This added custom logic overrides both _transfer() internal function and transferFrom() external function to calculate tax amounts and final amounts on each transfer:
function _transfer(
address _from,
address _to,
uint256 _amount
) internal override {
require(_to != address(0), "ERC20: transfer to the zero address");
uint256 tax = calculateTax(_amount);
uint256 amountAfterTax = _amount - tax;
// Tax is split between deployer and founder wallets
super._transfer(_from, deployerWallet, tax / 2);
super._transfer(_from, founderWallet, tax / 2);
super._transfer(_from, _to, amountAfterTax);
}
function transferFrom(
address _from,
address _to,
uint256 _value
) public override returns (bool success) {
uint256 tax = calculateTax(_value);
uint256 amountAfterTax = _value - tax;
// Distributing tax to both wallets
super.transferFrom(_from, deployerWallet, tax / 2);
super.transferFrom(_from, founderWallet, tax / 2);
return super.transferFrom(_from, _to, amountAfterTax);
}
Reference: CommunityCurrency.sol#L53-81
However, the transferFrom() overridden logic generates approximately double the intended tax rate. This is because transferFrom() function internally calls _transfer(), which is the overridden _transfer() function as well. Essentially, each super.transferFrom() call charging and transferring fees one additional time:
function transferFrom(address from, address to, uint256 amount) public virtual override returns (bool) {
address spender = _msgSender();
_spendAllowance(from, spender, amount);
_transfer(from, to, amount);
return true;
}
Reference: ERC20.sol#L158-163
It is worth noting that transferFrom() is one of the main external methods for third-party contract integrations to pull assets from the user with prior approval. This means all these integrations will incur approximately double the rate fee.
Remediations to Consider:
Consider removing the transferFrom() overridden function logic in CommunityCurrency.sol.
ERC20Base contract functions allow the owner to mint and burn tokens arbitrarily. Through functions mintTo() and burnFrom(), the owner can change any user’s balance. Minting schedules can be used to avoid the need for a single owner entity to manually mint tokens and keep the transparency of the supply within the code execution.
CommunityCurrency contract inherits the Permission extension from thirdweb’s library but does not use any role access control function or modifier.
Storage variables deployerWallet, founderWallet, and taxRate are set in the contract’s constructor and should be marked as immutable.
Macro makes no warranties, either express, implied, statutory, or otherwise, with respect to the services or deliverables provided in this report, and Macro specifically disclaims all implied warranties of merchantability, fitness for a particular purpose, noninfringement and those arising from a course of dealing, usage or trade with respect thereto, and all such warranties are hereby excluded to the fullest extent permitted by law.
Macro will not be liable for any lost profits, business, contracts, revenue, goodwill, production, anticipated savings, loss of data, or costs of procurement of substitute goods or services or for any claim or demand by any other party. In no event will Macro be liable for consequential, incidental, special, indirect, or exemplary damages arising out of this agreement or any work statement, however caused and (to the fullest extent permitted by law) under any theory of liability (including negligence), even if Macro has been advised of the possibility of such damages.
The scope of this report and review is limited to a review of only the code presented by the Shroom team and only the source code Macro notes as being within the scope of Macro’s review within this report. This report does not include an audit of the deployment scripts used to deploy the Solidity contracts in the repository corresponding to this audit. Specifically, for the avoidance of doubt, this report does not constitute investment advice, is not intended to be relied upon as investment advice, is not an endorsement of this project or team, and it is not a guarantee as to the absolute security of the project. In this report you may through hypertext or other computer links, gain access to websites operated by persons other than Macro. Such hyperlinks are provided for your reference and convenience only, and are the exclusive responsibility of such websites’ owners. You agree that Macro is not responsible for the content or operation of such websites, and that Macro shall have no liability to your or any other person or entity for the use of third party websites. Macro assumes no responsibility for the use of third party software and shall have no liability whatsoever to any person or entity for the accuracy or completeness of any outcome generated by such software.