# Overview

Code 432n4 (C4) is an open organization consisting of security researchers, auditors, developers, and individuals with domain expertise in smart contracts.

A C4 code contest is an event in which community participants, referred to as Wardens, review, audit, or analyze smart contract logic in exchange for a bounty provided by sponsoring projects.

During the code contest outlined in this document, C4 conducted an analysis of of the Gro Protocol smart contract system written in Solidity. The code contest took place between June 30 — July 7, 2021.

## Wardens

7 Wardens contributed reports to the Gro code contest:

This contest was judged by ghoul.sol.

Final report assembled by moneylegobatman and ninek.

# Summary

The C4 analysis yielded an aggregated total of 31 unique vulnerabilities. All of the issues presented here are linked back to their original finding

Of these vulnerabilities, 4 received a risk rating in the category of HIGH severity, 6 received a risk rating in the category of MEDIUM severity, and 21 received a risk rating in the category of LOW severity.

C4 analysis also identified 54 non-critical recommendations.

# Scope

The code under review can be found within the C4 Gro Protocol code contest repository is comprised of 61 smart contracts written in the Solidity programming language.

# Severity Criteria

C4 assesses the severity of disclosed vulnerabilities according to a methodology based on OWASP standards.

Vulnerabilities are divided into three primary risk categories: high, medium, and low.

High-level considerations for vulnerabilities span the following key areas when conducting assessments:

• Malicious Input Handling
• Escalation of privileges
• Arithmetic
• Gas use

Further information regarding the severity criteria referenced throughout the submission review process, please refer to the documentation provided on the C4 website.

# High Risk Findings (4)

## [H-01] implicit underflows

Submitted by gpersoon, also found by cmichel

There are a few underflows that are converted via a typecast afterwards to the expected value. If solidity 0.8.x would be used, then the code would revert.

• int256(a-b) where a and b are uint: For example, if a=1 and b=2, then the intermediate result would be uint(-1) == 2**256-1
• int256(-x) where x is a uint. For example, if x=1, then the intermediate result would be uint(-1) == 2**256-1

It’s better not to have underflows by using the appropriate typecasts. This is especially relevant when moving to solidity 0.8.x.

From Exposure.sol L178:

function sortVaultsByDelta(..)
..
for (uint256 i = 0; i < N_COINS; i++) {
// Get difference between vault current assets and vault target
int256 delta = int256(unifiedAssets[i] - unifiedTotalAssets.mul(targetPercents[i]).div(PERCENTAGE_DECIMAL_FACTOR)); // underflow in intermediate result

From PnL.sol L112:

 function decreaseGTokenLastAmount(bool pwrd, uint256 dollarAmount, uint256 bonus)...
..
emit LogNewGtokenChange(pwrd, int256(-dollarAmount)); // underflow in intermediate result

From Buoy3Pool.sol L87:

function safetyCheck() external view override returns (bool) {
...
_ratio = abs(int256(_ratio - lastRatio[i])); // underflow in intermediate result

Recommend replacing int256(a-b) with int256(a)-int256(b), and replacing int256(-x) with -int256(x)

kristian-gro (Gro) confirmed but disagreed with severity:

Confirmed and We’ve mitigated this issue in our release version.

ghoul-sol (Judge) commented:

Majority of overflow listed above seems low risk with one exception of safetyCheck. Underflow is a real risk here.safetyCheck is run every time a deposit is made. Ratios can change and the change does not need to be substantial for it to overflow. For that reason it’s a high risk.

## [H-02] Buoy3Pool.safetyCheck is not precise and has some assumptions

Submitted by cmichel, also found by shw

The safetyCheck function has several issues that impact how precise the checks are:

1. Only checks if the a/b and a/c ratios are within BASIS_POINTS. By transitivity, b/c is only within 2 * BASIS_POINTS if a/b and a/c are in range. For a more precise check whether both USDC and USDT are within range, b/c must be checked as well.
2. If a/b is within range, this does not imply that b/a is within range.
3. “inverted ratios, a/b bs b/a, while producing different results should both reflect the same change in any one of the two underlying assets, but in opposite directions”

4. Example: lastRatio = 1.0 ratio: a = 1.0, b = 0.8 => a/b = 1.25, b/a = 0.8 If a/b was used with a 20% range, it’d be out of range, but b/a is in range.
5. The NatSpec for the function states that it checks Curve and an external oracle, but no external oracle calls are checked, both _ratio and lastRatio are only from Curve. Only _updateRatios checks the oracle.

To address this issue, it is recommended to check if b/c is within BASIS_POINTS .

kristian-gro (Gro) confirmed but disagreed with severity:

Makes strong assumption about the range of possible values - small differences between a and b will result in small differences between a/b and b/a - Extreme cases are handled by emergency. Agree on b/c check

kristian-gro (Gro) commented:

medium severity - will only cause stop of deposits/withdrawals against curve, work around to put in emergency mode

kristian-gro (Gro) commented:

Acknowledged, but the differences between variables are in basis points, we’ve simulated flash loan manipulations of curve and come to the conclusion that this approximation has a sufficiently small error margin to not cause issues. The B/C check (usdc/usdt) has been added in release version.

ghoul-sol (Judge) commented:

A possibility of stopping deposits or withdrawals deserves high risk.

## [H-03] Incorrect use of operator leads to arbitrary minting of GVT tokens

Submitted by 0xRajeev, also found by pauliax and gpersoon

The distributeStrategyGainLoss() function distributes any gains or losses generated from a harvest and is expected to be called only by valid protocol vault adaptors. It is an externally visible function and the access control is indirectly enforced on msg.sender by checking that vaultIndexes[msg.sender] is a valid index range 1-4. However, the operator used in the require() is || instead of &&, which allows an arbitrary msg.sender, i.e. attacker, to bypass the check.

Scenario: An arbitrary non-vault address calling this function will get an index of 0 because of default mapping value in vaultIndexes[msg.sender], which will fail the > 0 check, but pass the <= N_COINS + 1 check (N_COINS = 3) because 0 <= 4 which will allow control to go past this check.

Furthermore, on L362, index=0 will underflow the -1 decrement (due to lack of SafeMath.sub and use of < 0.8.0 solc) and the index will be set to (uint256_MAX - 1). This will allow execution to proceed to the “else” part of conditional meant for curve LP vault. Therefore, this will allow any random address to call this function with arbitrary values of gain/loss and distribute arbitrary gain/loss appearing to come from Curve vault.

The attack control flow:

• -> Controller.distributeStrategyGainLoss(ARBITRARY_HIGH_VALUE_OF_GAIN, 0)
• -> index = 0 passes check for the index <= N_COINS + 1 part of predicate on L357 in Controller.sol
• -> index = uint256_MAX after L362
• -> gainUsd = ibuoy.lpToUsd(ARBITRARY_HIGH_VALUE_OF_GAIN); on L371 in Controller.sol
• -> ipnl.distributeStrategyGainLoss(gainUsd, lossUsd, reward); on L376 in Controller.sol
• -> (gvtAssets, pwrdAssets, performanceBonus) = handleInvestGain(lastGA, lastPA, gain, reward); on L254 in PnL.sol
• -> performanceBonus = profit.mul(performanceFee).div(PERCENTAGE_DECIMAL_FACTOR); on L186 of PnL.sol
• -> gvt.mint(reward, gvt.factor(gvtAssets), performanceBonus); on L256 in PnL.sol

Recommend changing || to && in require() on L357 of Controller.sol to prevent arbitrary addresses from going past this check. Or, consider exercising explicit access control for the authorized vault adaptors.

kristian-gro (Gro) confirmed

Confirmed and Fix has been implemented in release version.

## [H-04] sortVaultsByDelta doesn’t work as expected

Submitted by gpersoon, also found by shw

The function sortVaultsByDelta doesn’t always work as expected.

Suppose all the delta’s are positive, and delta1 >= delta2 >= delta3 > 0. Then maxIndex = 0. And (delta < minDelta (==0) ) is never true, so minIndex = 0.

Then (assuming bigFirst==true):

vaultIndexes[0] = maxIndex = 0
vaultIndexes[2] = minIndex = 0
vaultIndexes[1] = N_COINS - maxIndex - minIndex = 3-0-0 = 3

This is clearly not what is wanted, all vaultIndexes should be different and should be in the range [0..2]. This is due to the fact that maxDelta and minDelta are initialized with the value 0. This all could results in withdrawing from the wrong vaults and reverts (because vaultIndexes[1] is out of range).

Exposure.sol L178:

function sortVaultsByDelta(bool bigFirst,uint256 unifiedTotalAssets,uint256[N_COINS] calldata unifiedAssets,uint256[N_COINS] calldata targetPercents) external pure override returns (uint256[N_COINS] memory vaultIndexes) {
uint256 maxIndex;
uint256 minIndex;
int256 maxDelta;
int256 minDelta;
for (uint256 i = 0; i < N_COINS; i++) {
// Get difference between vault current assets and vault target
int256 delta = int256(
unifiedAssets[i] - unifiedTotalAssets.mul(targetPercents[i]).div(PERCENTAGE_DECIMAL_FACTOR)
);
// Establish order
if (delta > maxDelta) {
maxDelta = delta;
maxIndex = i;
} else if (delta < minDelta) {
minDelta = delta;
minIndex = i;
}
}
if (bigFirst) {
vaultIndexes[0] = maxIndex;
vaultIndexes[2] = minIndex;
} else {
vaultIndexes[0] = minIndex;
vaultIndexes[2] = maxIndex;
}
vaultIndexes[1] = N_COINS - maxIndex - minIndex;
}

Recommend the following

1. Initializing maxDelta and minDelta:

    int256 maxDelta = -2**255; // or type(int256).min when using a newer solidity version
int256 minDelta  = 2**255; // or type(int256).max when using a newer solidity version
2. Check that maxIndex and minIndex are not the same
3. require (maxIndex != minIndex);

kristian-gro (Gro) confirmed:

Confirmed and Fix has been implemented in release version.

# Medium Risk Findings (6)

Submitted by cmichel, also found by 0xRajeev and adelamo_

The Chainlink API (latestAnswer) used in the Buoy3Pool oracle wrappers is deprecated:

This API is deprecated. Please see API Reference for the latest Price Feed API. Chainlink Docs

It seems like the old API can return stale data. Checks similar to that of the new API using latestTimestamp and latestRoundare are needed, as this could lead to stale prices according to the Chainlink documentation:

Recommend adding checks similar to latestTimestamp and latestRoundare

(
uint80 roundID,
int256 price,
,
uint256 timeStamp,
require(
timeStamp != 0,
);
require(
);
require(price != 0, "Chainlink Malfunction”);

kristian-gro (Gro) confirmed

Confirmed and Fix has been implemented in release version.

Submitted by 0xRajeev, also found by pauliax

The addSafeAddress() takes an address and adds it to a “safe list”. This is used in eoaOnly() to give exemption to safe addresses that are trusted smart contracts, when all other smart contacts are prevented from protocol interaction. The stated purpose is to allow only such partner/trusted smart contract integrations (project rep mentioned Argent wallet as the only one for now but that may change) an exemption from potential flash loan threats. But if there is a safe listed integration that needs to be later disabled, it cannot be done. The protocol will have to rely on other measures (outside the scope of this contest) to prevent flash loan manipulations which are specified as an area of critical concern.

Scenario: A trusted integration/partner address is added to the safe list. But that wallet/protocol/DApp is later manipulated (by the project, its users or an attacker) to somehow launch a flash loan attack on the protocol. However, its address cannot be removed from the safe list and the protocol cannot prevent flash loan manipulations from that source because of its exemption. Contract/project will have to be redeployed.

Recommend changing addSafeAddress() to isSafeAddress() with an additional bool parameter to allow both the enabling AND disabling of safe addresses.

kristian-gro (Gro) confirmed but disagreed with severity:

low risk - Made specifically for one partner in beta period, and planned to be removed. We added the removal function for sanity.

Confirmed and Fix has been implemented in release version.

ghoul-sol (Judge) commented:

I’ll keep medium risk because this could put the protocol into a one way street and not being able to remove safe addresses is quite dangerous. Medium risk.

## [M-03] BaseVaultAdaptor assumes sharePrice is always in underlying decimals

Submitted by cmichel

The two BaseVaultAdaptor.calculateShare functions compute share = amount.mul(uint256(10)**decimals).div(sharePrice)

uint256 sharePrice = _getVaultSharePrice();
// amount is in "token" decimals, share should be in "vault" decimals
share = amount.mul(uint256(10)**decimals).div(sharePrice);

This assumes that the sharePrice is always in token decimals and that token decimals is the same as vault decimals.

Both these assumptions happen to be correct for Yearn vaults, but that will not necessarily be the case for other protocols. As this functionality is in the BaseVaultAdaptor, and not in the specific VaultAdaptorYearnV2_032, consider generalizing the conversion.

Integrating a token where the token or price is reported in a different precision will lead to potential losses as more shares are computed.

Because the conversion seems highly protocol-specific, it is recommended that calculateShare should be an abstract function (like _getVaultSharePrice) that is implemented in the specific adaptors.

- kristian-gro (Gro) confirmed

Confirmed and shares have been removed from release version.

## [M-04] Flash loan risk mitigation is optional and not robust enough

Submitted by 0xRajeev

The switchEoaOnly() allows the owner to disable preventSmartContracts (the project’s plan apparently is to do so after the beta-period) which will allow any smart contract to interact with the protocol and potentially exploit any underlying flash loan vulnerabilities which are specified as an area of critical concern.

The current mitigation is to optionally prevent contracts, except whitelisted partner ones, from interacting with the protocol to prevent any flash loan manipulations. A more robust approach would be to add logic preventing multiple txs to the protocol from the same address/tx.origin within the same block when smart contracts are allowed. This will avoid any reliance on trust with integrating partners/protocols.

Recommend adding logic that prevents multiple txs to the protocol from the same address and within the same block.

kristian-gro (Gro) acknowledged but disagreed with severity:

Low-severity: This is a temporary blocker to not let SCs interact with gro-protocol, planned to be removed after beta as it might potentially stop other integrations (as per issue 51)

Acknowledged, this is just a temporary block, and is planned to be removed in future releases - other protection exists to protect the system from flash loan manipulations.

ghoul-sol (Judge) commented:

It looks like a low risk issue since it’s a future problem and not something that is an immediate issue, however, it’s not clear how the protocol will protect itself against flash loans after this temporary blocker is off. One of the critical protocol’s concerns are flash loans manipulations therefore I think medium risk is justified here.

Submitted by shw

According to Chainlink’s documentation (Deprecated API Reference, Migration Instructions, and API Reference), the latestAnswer function is deprecated. This function does not throw an error if no answer has been reached, but instead returns 0, causing an incorrect price to be fed to the Buoy3Pool. See Buoy3Pool.sol L207 and L214-L216.

Recommend using the latestRoundData function to get the price instead. Also recommend adding checks on the return data with proper revert messages if the price is stale or the round is incomplete, for example:

(uint80 roundID, int256 price, , uint256 timeStamp, uint80 answeredInRound) = oracle.latestRoundData();
require(timeStamp != 0, "...");

kristian-gro (Gro) disagreed with severity:

disagree with severity (Low risk) Issue would cause deposits and withdrawals to stop, no funds lost

kristian-gro (Gro) confirmed:

Confirmed and shares have been removed from release version.

ghoul-sol (Judge) commented:

In my opinion halting the protocol deserves medium risk. While no funds are lost, from brand perspective it’s a second worst thing. Keeping as medium risk.

## [M-06] Early user can break minting

Submitted by cmichel

The protocol computes a factor when minting (and burning) tokens, which is the exchange rate of rebase to base tokens (base supply / total assets value), see GToken.factor(). The first user can manipulate this factor such that it always returns 0.

Example:

• Attacker deposits 100.0 DAI and mints 100 * 1e18 PWRD: DepositHandler.depositGToken with dollarAmount = 100.0 = 100 * 1e18, then ctrl.mintGToken(pwrd, msg.sender, 1e18) calls gt.mint(account, gt.factor(), amount=1e18) where gt.factor() returns getInitialBase() = 1e18 because the person is the first minter and it mints amount * factor / _BASE = 1e18
• The ctrl.mintGToken call also increases total assets: pnl.increaseGTokenLastAmount(...)
• The attacker now burns (withdraws) all minted tokens again except a single wei using one of the withdrawal functions in WithdrawHandler. Because of the withdrawal fee the total assets are only decreased by the post-fee amount (IPnL(pnl).decreaseGTokenLastAmount(pwrd, amount=userBalance - 1, bonus=fee);), i.e., with a 2% withdrawal fee the total assets stay at 2% of 100\$ = 2 * 1e18.
• The result is that GToken.factor() always returns totalSupplyBase().mul(BASE).div(totalAssets) = 1 * 1e18 / (2 * 1e18) = 0

The resulting factor is 0 and thus any user-deposits by depositGToken will mint 0 base tokens to the depositor. This means all deposits and future value accrues to the attacker who holds the only base tokens.

An attacker could even front-run the first minter to steal their deposit this way.

Uniswap solves a similar problem by sending the first 1000 tokens to the zero address which makes the attack 1000x more expensive. The same should work here, i.e., on first mint (total base supply == 0), lock some of the first minter’s tokens by minting ~1% of the initial amount to the zero address instead of to the first minter.

kristian-gro (Gro) acknowledged but disagreed with severity:

Known issue which will be handled by ops - low risk as gro protocol is the first depositor

ghoul-sol (Judge) commented:

Even though it’s a known issue its consequences are significant. Only because it can be mitigated by ops quite easily, I’ll degrade it to medium level.

# Low Risk Findings

## [L-01] emergencyHandler not checked & not emitted

Submitted by gpersoon, also found by shw

The function setWithdrawHandler allows the setting of withdrawHandler and emergencyHandler. However, emergencyHandler isn’t checked for 0 (like the withdrawHandler ). The value of the emergencyHandler is also not emitted (like the withdrawHandler )

Controller.sol L105:

function setWithdrawHandler(address _withdrawHandler, address _emergencyHandler) external onlyOwner {
withdrawHandler = _withdrawHandler;
emergencyHandler = _emergencyHandler;
emit LogNewWithdrawHandler(_withdrawHandler);
}

    require(_emergencyHandler!= address(0), "setEmergencyHandler: 0x");
emit LogNewEmergencyHandler(_emergencyHandler);

- kristian-gro (Gro) confirmed

## [L-02] lastRatio of Buoy3Pool is not initialized

Submitted by gpersoon

The values of lastRatio in the contract Buoy3Pool.sol are not initialized (thus they have a value of 0). If safetyCheck() would be called before the first time _updateRatios is called, then safetyCheck() would give unexpected results.

Buoy3Pool.sol L25:

contract Buoy3Pool is FixedStablecoins, Controllable, IBuoy, IChainPrice {
...
mapping(uint256 => uint256) lastRatio;

function safetyCheck() external view override returns (bool) {
for (uint256 i = 1; i < N_COINS; i++) {
uint256 _ratio = curvePool.get_dy(int128(0), int128(i), getDecimal(0));
_ratio = abs(int256(_ratio - lastRatio[i]));
if (_ratio.mul(PERCENTAGE_DECIMAL_FACTOR).div(CURVE_RATIO_DECIMALS_FACTOR) > BASIS_POINTS) {
return false;
}
}
return true;
}

function _updateRatios(uint256 tolerance) private returns (bool) {
...
for (uint256 i = 1; i < N_COINS; i++) {
lastRatio[i] = newRatios[i];

Recommend double checking if this situation can occur and perhaps calling _updateRatios as soon as possible. Or alternatively, check in safetyCheck that the lastRatio values are initialized.

- kristian-gro (Gro) acknowledged

## [L-03] Buoy3Pool._updateRatios unsafe math

Submitted by cmichel

The function performs type conversions and subtraction without over-/underflow checks:

uint256 check = abs(int256(_ratio) - int256(chainRatios[i].div(CHAIN_FACTOR)));

Recommend checking if the values fit within the type range first, otherwise revert with a meaningful error message, as well as checking for underflows.

ghoul-sol (Judge) commented:

This is partially a duplicate of #6 but it focuses on low risk issue so I’ll record is as a separate (low risk) issue.

## [L-04] setUnderlyingTokenPercent should check percentages

Submitted by gpersoon, also found by cmichel

The function setUnderlyingTokenPercent doesn’t check that the sum of all the percentages is 100%. This way the percentages could be accidentally set up the wrong way, with unpredictable results. Note that the function can only be called by controller or the owner so the likelihood of mistakes is pretty low.

Insurance.sol #L100:

function setUnderlyingTokenPercent(uint256 coinIndex, uint256 percent) external override onlyValidIndex(coinIndex) {
require(msg.sender == controller || msg.sender == owner(), "setUnderlyingTokenPercent: !authorized");
underlyingTokensPercents[coinIndex] = percent;
emit LogNewTargetAllocation(coinIndex, percent);
}

Recommend changing setUnderlyingTokenPercent to set the percentages for all the coins at the same time. And check that the sum of the percentages is 100%

## [L-05] initialize maxPercentForWithdraw and maxPercentForDeposit?

Submitted by gpersoon

The parameters maxPercentForWithdraw and maxPercentForDeposit, which are not directly initialized, will work in a suboptimal way If, the functions which rely on these parameters, are called before setWhaleThresholdWithdraw/setWhaleThresholdDeposit.

Insurance.sol L63:

uint256 public maxPercentForWithdraw;
uint256 public maxPercentForDeposit;

function setWhaleThresholdWithdraw(uint256 _maxPercentForWithdraw) external onlyOwner {
maxPercentForWithdraw = _maxPercentForWithdraw;
emit LogNewVaultMax(false, _maxPercentForWithdraw);
}
function setWhaleThresholdDeposit(uint256 _maxPercentForDeposit) external onlyOwner {
maxPercentForDeposit = _maxPercentForDeposit;
emit LogNewVaultMax(true, _maxPercentForDeposit);
}

Recommend assigning a default value to maxPercentForWithdraw and maxPercentForDeposit. Or alternatively, initializing the values via the constructor.

kristian-gro (Gro) acknowledged:

This is known and values are updated as part of deployment scripts

## [L-06] use safemath

Submitted by gpersoon

Safemath is used in several places but not everywhere. Especially in risky places like PnL and distributeStrategyGainLoss where it is hardly worth the gas-savings of not using safemath.

In distributeStrategyGainLoss it does make a difference, also due to another issue.

function handleLoss( uint256 gvtAssets, uint256 pwrdAssets, uint256 loss) private pure returns (uint256, uint256) {
uint256 maxGvtLoss = gvtAssets.sub(DEFAULT_DECIMALS_FACTOR);
if (loss > maxGvtLoss) {
...
} else {
gvtAssets = gvtAssets - loss;    // won't underflow but safemath won't hurt
}

function forceDistribute() private {
uint256 total = _controller().totalAssets();
lastGvtAssets = total - lastPwrdAssets;   // won't underflow but safemath won't hurt
} else {
...

Controller.sol L355

function distributeStrategyGainLoss(uint256 gain, uint256 loss) external override {
uint256 index = vaultIndexes[msg.sender];
require(index > 0 || index <= N_COINS + 1, "!VaultAdaptor");    // always true, see separate issue
..
index = index - 1;  // can underflow

Recommend applying safemath or moving to Solidity 0.8.x

- kristian-gro (Gro) acknowledged

## [L-07] Missing emits for declared events

Submitted by 0xRajeev, also found by cmichel

Missing emits for declared events indicate potentially missing logic, redundant declarations, or reduced off-chain monitoring capabilities.

Scenario: For example, the event LogFlashSwitchUpdated is missing an emit in Controller.sol. Based on the name, this is presumably related to flash loans being enabled/disabled which could have significant security implications. Or the (misspelled) LogHealhCheckUpdate which is presumably related to a health check logic that is missing in LifeGuard. See issue page for referenced code.

Recommend evaluating if logic is missing and if so, adding logic+emit or removing event.

kristian-gro (Gro) confirmed

## [L-08] Having only owner unpause/restart is risky

Submitted by 0xRajeev

The design choice seems to allow a whitelist of addresses (bots or trusted parties) that can trigger pause/emergency but onlyOwner can unpause/restart (and perform other privileged functions). While it is recommended in general to have separate privileges/roles for stopping and starting critical functions, having only a single owner for unpause/restart triggering may create a single point of failure if owner is EOA and keys are lost/compromised.

Scenario: Protocol is paused or put in emergency mode by a bot/user in whitelist. Owner is an EOA and the private keys are lost. Protocol cannot be unpaused/restarted. See Controller.sol #L317, #L101, and #L97.

Recommend evaluating this design choice to see if a whitelist should also be allowed to unpause/restart. At a minimum, use a 6-of-9 or higher multisig and not an EOA.

kristian-gro (Gro) acknowledged:

Multi sig planned

Submitted by 0xRajeev

Uninitialized system/curve vaults (default to zero address) will lead to reverts on calls and expect owner to set them before other functions are called because functions do not check if system has been initialized. This requires a robust deployment script which is fail-safe.

The same applies to many other address parameters in the protocol e.g.: reward.

Scenario: All vaults are not initialized because of a script error or an admin mistake. Protocol goes live and user interactions result in exceptions. Users lose trust and protocol reputation takes a hit. See Controller.sol #L136-L150 and #L194-L198.

Recommend evaluating non-zero defaults, initializing from constructor or maintaining/checking an initialization state variable which prevents other functions from being called until all critical system states such as vault addresses are initialized.

kristian-gro (Gro) acknowledged:

Controller by gro governance, dealt with in deployment scripts

## [L-10] The use of tx.origin for smart contract safe list is risky and not generic

Submitted by 0xRajeev

The addSafeAddress() takes an address and adds it to a “safe list”. This is used in eoaOnly() to give exemption to safe addresses that are trusted smart contracts, when all other smart contacts are prevented from protocol interaction. The stated purpose is to allow only such partner/trusted smart contract integrations (project rep mentioned Argent wallet as the only one for now but that may change) an exemption from potential flash loan threats.

The eoaOnly() check used during deposits and withdrawals checks if preventSmartContracts is enabled and if so, makes sure the transaction is coming from an integration/partner smart contract. But instead of using msg.sender in the check it uses tx.origin. This is suspect because tx.origin gives the originating EOA address of the transaction and not a smart contract’s address. (This may get even more complicated with the proposed EIP-3074.)

Discussion with the project team indicated that this is indeed not the norm but is apparently the case for their only current (none others planned) integration with Argent wallet where the originating account is Argent’s relayer tx.origin i.e. flow:

Argent relayer (tx.origin) => Argent user wallet (msg.sender) => gro protocol while the typically expected flow is: user EOA (tx.origin) => proxy (msg.sender) => gro protocol.

While this has reportedly been verified and tested, it does seem strange and perhaps warrants a re-evaluation because the exemption for this/other trusted integration/partner smart contracts will not work otherwise.

Scenario: Partner contract is added to the safe address for exemption but the integration fails because of the use of tx.origin instead of msg.sender. See Controller.sol #L266-L272, #L176-L178, and #L171-L174.

Recommend re-evaluating the use of tx.origin instead of msg.sender.

kristian-gro (Gro) acknowledged:

Made for specific partner, so cannot be generic

While this has reportedly been verified and tested, it does seem strange and perhaps warrants a re-evaluation because the exemption for this/other trusted integration/partner smart contracts will not work otherwise.

This SC protection is only temporary as we are aware of EIP-3074, and consideration of how we need to change this/or if we need this at all are ongoing.

## [L-11] Missing parameter validation

Submitted by cmichel, also found by 0xRajeev

Some parameters of functions are not checked for invalid values:

• BaseVaultAdaptor.constructor: The addresses should be checked for non-zero values
• LifeGuard3Pool.constructor: The addresses should be checked for non-zero values
• Buoy3Pool.constructor: The addresses should be checked for non-zero values
• PnL.constructor: The addresses should be checked for non-zero values
• Controllable.setController: Does not check that newController != controller

A wrong user input, or wallets defaulting to the zero addresses for a missing input, can lead to the contract needing to redeploy or wasted gas.

Recommend validating the parameters.

kristian-gro (Gro) acknowledged:

Low risk/Non critical - Deployment script handles these cases, but good practice to have 0x checks to stop wasting gas and having to redeploy.

## [L-12] Stricter than needed inequalities may affect borderline scenarios

Submitted by 0xRajeev

Token amounts/prices are typically open-ranged and inclusive of the bounds. Using ‘<‘ or ‘>’ instead of ‘<=‘ and ‘>=‘ may affect borderline scenarios, be considered unintuitive by users, and affect accounting.

-Scenario 1: In calculateVaultSwapData(), the require() check is:

require(withdrawAmount < state.totalCurrentAssetsUsd, "Withdrawal exceeds system assets");

The ‘<‘ could be replaced by ‘<=‘

Scenario 2: In withdrawSingleByLiquidity(), the require() check is:

require(balance > minAmount, "withdrawSingle: !minAmount");

The ‘>’ should be ‘>=‘ as is used in the similar check in withdrawSingleByExchange().

See Insurance.sol L429, and LifeGuard3Pool.sol L224 and L268.

Recommend reconsidering strict inequalities and relaxing them if possible.

kristian-gro (Gro) acknowledged:

We haven’t been able to model an exploit for this

## [L-13] totalAssets > withdrawelUsd should be inclusive

Submitted by pauliax

The check should be inclusive here to cover the case when totalAssets = withdrawalUsd:

Recommend changing

require(totalAssets > withdrawUsd, "totalAssets < withdrawalUsd");

to

require(totalAssets >= withdrawUsd, "totalAssets < withdrawalUsd");

kristian-gro (Gro) acknowledged:

Edge case that is unlikely to cause issues as gro protocol provides initial seed investment

## [L-14] Use of uninitialized value and unclear/unused logic

Submitted by 0xRajeev, also found by cmichel

vaultIndexes is uninitialized and it’s unclear what 10000 signifies here. investDelta return value is also ignored at call site. If this is an indication of missed/incorrect logic, then it’s risky. If not, removing will help readability/maintainability. See Insurance.sol #L166, and #L155.

Recommend evaluating any missing logic or else removing unused code.

- kristian-gro (Gro) confirmed

## [L-15] decimals of FixedStablecoins

Submitted by pauliax

The FixedStablecoins constructor does not validate that addresses in the array are not empty, != address(0), and instead relies on the creator passing the correct values for decimals. The comment next to USDC (0xA0b86991c6218b36c1d19D4a2e9Eb0cE3606eB48) says that it is supposed to have 6 decimals:

    uint256 public immutable USDC_DECIMALS; // = 1E6;

However, when querying the actual value on Etherscan, it shows 0 decimals: The problem with USDC is that it uses a proxy pattern, thus the implementation could change (decimals could change but in practice, I think it is very unlikely).

I think it would be better not to pass decimals separately and, instead of relying on the correctness of the input, recommend using IERC20Detailed to query the decimals in code. Always querying the decimals on the go may be very inefficient and bring new attack vectors so I think you need to do here an assumption that decimals of upgradeable tokens won’t change.

kristian-gro (Gro) acknowledged:

We dont expect to see any changes to underlying decimals of stablecoins, worst case scenario we can redeploy the affected contracts

## [L-16] More accurate calculation of return USD of withdrawSingleByLiquidity

Submitted by shw

The withdrawSingleByLiquidity function of LifeGuard3Pool calls buoy.singleStableToUsd to calculate the return USD amount, which internally calls _stableToUsd with the deposit parameter set to true. A more accurate calculation is to set the deposit parameter to false since this action is a withdrawal. A similar issue exists in the function calcProtocolWithdraw of Allocation, where the current strategy’s USD is calculated by buoy.singleStableToUsd. See LifeGuard3Pool.sol #L226, Buoy3Pool.sol #L122, and Allocation.sol #L142.

Recommend considering adding a new boolean parameter, deposit, to the singleStableToUsd function of Buoy3Pool to indicate whether the action is a deposit or not, as that in the stableToUsd and stableToLp functions.

- kristian-gro (Gro) confirmed

## [L-17] Use of tx.origin for authentication

Submitted by shw

The eoaOnly function of Controller checks whether the user is whitelisted using tx.origin. Using tx.origin to authenticate users is generally not a good practice since it can be abused by malicious contracts when whitelisted users are interacting with them. Users have to be very careful to avoid being impersonated when interacting with contracts from other protocols, which could unnecessarily burden users. See Controller.sol #L269. For for more discussion on tx.origin, refer to Solidity issue - Remove tx.origin.

Recommend changing tx.origin at line 269 to msg.sender to ensure that the entity calling the Controller is the one allowed.

ghoul-sol (Judge) commented:

This issue touches on different problem so I’ll keep it as stand-alone low risk issue.

## [L-18] Vault assets can be migrated to an arbitrary address at anytime by owner

Submitted by 0xRajeev, also found by gpersoon

BaseVaultAdaptor contains logic that is “built on top of any vault in order for it to function with Gro protocol.” One of such functions is the migrate() function which is onlyOwner and takes an address parameter which allows owner to migrate the vault’s entire balance at any time to that address. This is extremely risky because it gives an opportunity for, or at least a perception of, a rug-pull by a disgruntled/malicious owner/dev to the protocol users/community. This could also be dangerous if triggered accidentally, especially by an EOA owner address or maliciously via compromised keys.

• Scenario 1: Protocol launches and starts accumulating TVL. A savvy user analyzes source and shares the presence of this migrate() function as potential owner rug-pull vector. Users withdraw funds and protocol reputation takes a hit.
• Scenario 2: Protocol launches and hits 100MM TVL. A disgruntled dev/owner migrates vault assets to their address and drains the protocol.
• Scenario 3: Protocol launches and hits 100MM TVL. Owner EOA keys get compromised and attacker migrates vault assets to their address and drains the protocol.

See similar concern on migrate() functionality in ShibaSwap recently from Yearn devs here and here. Also from here and here.

Recommend evaluating the need for this function and then avoiding/mitigating the risk appropriately.

kristian-gro (Gro) confirmed but disagreed with severity:

Low risk

• Owner is timelock, plan for multi sig. -assumes malicious owner

ghoul-sol (Judge) commented:

Agree with sponsor. Assuming malicious behavior of owner is low risk if it’s a governance and timelock is used. Low risk.

## [L-19] Enabling preventSmartContracts may lead to lock/loss of funds

Submitted by 0xRajeev

preventSmartContracts is initialized to false, which allows users to deposit/withdraw funds from the protocol via (custom) smart contracts because the eoaOnly check during deposits/withdrawals always succeeds. However, if protocol owner decides to suddenly enable preventSmartContracts, then smart contracts are prevented from interaction unless they are exempted in safe addresses.

The lack of an event in switchEoaOnly() to inform off-chain monitors /interfaces about the enabling/disabling, say from false -> true, and lack of a time-delayed enforcement of this prevention of contracts from depositing/withdrawing, causes users who have previously deposited via smart contracts (that are not safeAddresses) to get locked out of withdrawals leading to fund lock/loss.

Scenario: User deposits funds via smart contract (not in safe address list) when preventSmartContracts=false. Protocol owner sets preventSmartContracts=true. User’s funds are locked/lost in protocol. See issue page for affected code.

Recommend adding event + time-delayed enforcement to switchEoaOnly() so users can monitor and withdraw funds deposited via smart contracts.

kristian-gro (Gro) disputed:

Low criticality/Not an issue - Workaround exists (safe addresses)

• Owner will be a timelock

ghoul-sol (Judge) commented:

Agree with sponsor. While the scenario is correct, it all comes down to the management of the protocol. From different context I also assume that this option will be set to true for beta and safe addresses will be whitelisted. I’m making this a low risk because this can create too many angry users to be non-critical.

## [L-20] Unauthorized rebalanceTrigger calls may allow one to exploit arbitrage opportunity and put system at risk

Submitted by 0xRajeev

The need for an externally visible rebalanceTrigger() (when rebalance() does that check itself) is apparently that the whitelisted bot checks trigger before calling the very expensive/security-sensitive rebalance() operation which again checks to see if anything has changed between then and the previous trigger.

Exposing the rebalance trigger check externally for convenience may offer a front-running arbitrage opportunity to a non-whitelisted, i.e. any, bot which can check when a rebalance will be triggered by a whitelisted bot and then using that information to arbitrage on underlying stablecoins/strategies, which may affect system exposure.

Discussion with the project team reported that this is technically possible, but only within the BP limit (25-50) of the current vs cached price (where the BASIS_POINTS is currently set to 20). If not, the Buoy safetyCheck will fail. See Insurance.sol #L187-L196 and #L198-L215. Also Buoy3Pool.sol #L30.

Recommend adding onlyWhitelist modifier to rebalanceTrigger(), which allows retaining the convenience of (only whitelisted) bots checking before calling rebalance. This makes it only a little safer because one can always front-run the actual rebalance call. This will only force bots to monitor mempool for rebalances instead of arbing ahead of time. Revisit this aspect for any missed considerations.

kristian-gro (Gro) acknowleged and disagreed:

There is price check before rebalance. It is not very useful to add whitelist on view function. Because the code is public, anyone can implement a local function easily.

ghoul-sol (Judge) commented:

Solution proposed by warden does not solve the problem but the problem still remains valid. The issue looks quite generic and it’s really a MEV problem that most protocols have. For that reason, I think it’s reasonable to degrade to low risk.

## [L-21] Rational actors will just set themselves as referral

Submitted by cmichel

When depositing, a referral can be chosen and the only check is:

account != address(0) && referral != address(0) && referrals[account] == address(0)

This means that users can refer themselves. It’s not immediately clear from the contracts that are part of this repo, what the referrals are used for. If they are used for anything, rational actors will always refer themselves to maximize profits making the referral system useless.

Recommend whitelisting big influencers that are allowed to be used as referrals to avoid everyone referring themselves or another account they control.

kristian-gro (Gro) disputed and disagreed with severity:

not an issue/non-critical Makes no difference, referrals are calculated offchain and not used for anything on chain

ghoul-sol (Judge) commented:

Even if this is calculated off-chain, technically being able to refer ourselves is an issue. Even offchain this needs to be filtered out which is extra work. I’m keeping this as low risk.

# Disclosures

C4 is an open organization governed by participants in the community.

C4 Contests incentivize the discovery of exploits, vulnerabilities, and bugs in smart contracts. Security researchers are rewarded at an increasing rate for finding higher-risk issues. Contest submissions are judged by a knowledgeable security researcher and solidity developer and disclosed to sponsoring developers. C4 does not conduct formal verification regarding the provided code but instead provides final verification.

C4 does not provide any guarantee or warranty regarding the security of this project. All smart contract software should be used at the sole risk and responsibility of users.