C4-001 : Use `_safeMint()` instead of `_mint()`

Impact - LOW

OpenZeppelin recommends the usage of _safeMint() instead of _mint(). If the recipient is a contract, safeMint() checks whether they can handle ERC721 tokens.

Proof of Concept

If the HUB provides an address that can't handle ERC721 tokens when calling mint the minted token might be lost. That would also result in the user not being able to redeem the token anymore.

Navigate to the following contract functions and variables.

https://github.com/code-423n4/2022-02-aave-lens/blob/aaf6c116345f3647e11a35010f28e3b90e7b4862/contracts/core/CollectNFT.sol#L52

https://github.com/code-423n4/2022-02-aave-lens/blob/aaf6c116345f3647e11a35010f28e3b90e7b4862/contracts/core/FollowNFT.sol#L69

https://github.com/code-423n4/2022-02-aave-lens/blob/aaf6c116345f3647e11a35010f28e3b90e7b4862/contracts/core/LensHub.sol#L149

Tools Used

Code Review

Recommended Mitigation Steps

Use _safeMint() whenever possible.

C4-002 : Critical changes should use two-step procedure

Impact - LOW

Use a two-step process (new controllership proposition in one transaction and controllership acceptance in another). This function has no validations, even a simple check for zero-address is missing, and there is no validation of the new address being correct. If the admin accidentally uses an invalid address for which they do not have the private key, then the system gets locked because the swivel cannot be corrected and none of the other functions that require admin caller can be executed. A similar issue was reported in a previous contest and was assigned a severity of medium: code-423n4/2021-06-realitycards-findings#105

for Ex : -Alice deploys a new version of the whitehack group address. When she invokes the whitehack group address setter to replace the address, she accidentally enters the wrong address. The new address now has access to the role immediately and is too late to revert

Proof of Concept

Navigate to the following contract function. The critical process should be two step.

https://github.com/code-423n4/2022-02-aave-lens/blob/main/contracts/core/LensHub.sol#L83

https://github.com/code-423n4/2022-02-aave-lens/blob/main/contracts/core/LensHub.sol#L78

https://github.com/code-423n4/2022-02-aave-lens/blob/main/contracts/core/FollowNFT.sol#L78

https://github.com/code-423n4/2022-02-aave-lens/blob/main/contracts/core/FollowNFT.sol#L83

Tools Used

None

Recommended Mitigation Steps

Lack of two-step procedure for critical operations leaves them error-prone. Implement zero address check and Consider implementing a two step process where the owner nominates an account and the nominated account needs to call an acceptOwnership() function for the transfer of ownership to fully succeed. This ensures the nominated EOA account is a valid and active account.

C4-003 : Missing zero-address check in constructors and the setter functions

Impact - LOW

Missing checks for zero-addresses may lead to infunctional protocol, if the variable addresses are updated incorrectly. For instance, If HUB variable is added as a zero address minting functionality will be lost.

Proof of Concept

Navigate to the following contract functions and variables.

https://github.com/code-423n4/2022-02-aave-lens/blob/main/contracts/core/LensHub.sol#L58

https://github.com/code-423n4/2022-02-aave-lens/blob/main/contracts/core/LensHub.sol#L59

https://github.com/code-423n4/2022-02-aave-lens/blob/main/contracts/core/LensHub.sol#L70

https://github.com/code-423n4/2022-02-aave-lens/blob/main/contracts/core/FollowNFT.sol#L49

https://github.com/code-423n4/2022-02-aave-lens/blob/main/contracts/core/CollectNFT.sol#L30

Tools Used

Code Review

Recommended Mitigation Steps

Consider adding zero-address checks in the discussed constructors: require(newAddr != address(0));.

C4-004 : Incompatibility With Rebasing/Deflationary/Inflationary tokens

Impact - LOW

The protocol do not appear to support rebasing/deflationary/inflationary tokens whose balance changes during transfers or over time. The necessary checks include at least verifying the amount of tokens transferred to contracts before and after the actual transfer to infer any fees/interest.

Proof of Concept

Navigate to the following contract.

https://github.com/code-423n4/2022-02-aave-lens/blob/aaf6c116345f3647e11a35010f28e3b90e7b4862/contracts/core/modules/follow/FeeFollowModule.sol#L89

https://github.com/code-423n4/2022-02-aave-lens/blob/aaf6c116345f3647e11a35010f28e3b90e7b4862/contracts/core/modules/collect/LimitedTimedFeeCollectModule.sol#L164

Tools Used

Manual Code Review

Recommended Mitigation Steps

Ensure that to check previous balance/after balance equals to amount for any rebasing/inflation/deflation
Add support in contracts for such tokens before accepting user-supplied tokens
Consider supporting deflationary / rebasing / etc tokens by extra checking the balances before/after or strictly inform your users not to use such tokens if they don't want to lose them.

C4-005 : Use of Block.timestamp

Impact - Non-Critical

Block timestamps have historically been used for a variety of applications, such as entropy for random numbers (see the Entropy Illusion for further details), locking funds for periods of time, and various state-changing conditional statements that are time-dependent. Miners have the ability to adjust timestamps slightly, which can prove to be dangerous if block timestamps are used incorrectly in smart contracts.

Proof of Concept

Navigate to the following contract.

https://github.com/code-423n4/2022-02-aave-lens/blob/aaf6c116345f3647e11a35010f28e3b90e7b4862/contracts/libraries/PublishingLogic.sol#L165

https://github.com/code-423n4/2022-02-aave-lens/blob/aaf6c116345f3647e11a35010f28e3b90e7b4862/contracts/core/FollowNFT.sol#L239

https://github.com/code-423n4/2022-02-aave-lens/blob/aaf6c116345f3647e11a35010f28e3b90e7b4862/contracts/core/base/LensMultiState.sol#L38

https://github.com/code-423n4/2022-02-aave-lens/blob/aaf6c116345f3647e11a35010f28e3b90e7b4862/contracts/core/CollectNFT.sol#L45

Tools Used

Manual Code Review

Recommended Mitigation Steps

Block timestamps should not be used for entropy or generating random numbers—i.e., they should not be the deciding factor (either directly or through some derivation) for winning a game or changing an important state.

Time-sensitive logic is sometimes required; e.g., for unlocking contracts (time-locking), completing an ICO after a few weeks, or enforcing expiry dates. It is sometimes recommended to use block.number and an average block time to estimate times; with a 10 second block time, 1 week equates to approximately, 60480 blocks. Thus, specifying a block number at which to change a contract state can be more secure, as miners are unable to easily manipulate the block number.

C4-006 : Missing Setter Function On The Client Variable

Impact - Non-Critical

Based on the context, client should be able to be updated after deployment. However, there is no function to update it.

Proof of Concept

Navigate to the following contract.

https://github.com/code-423n4/2022-02-aave-lens/blob/aaf6c116345f3647e11a35010f28e3b90e7b4862/contracts/core/CollectNFT.sol#L51

HUB is only set in the constructor.

Tools Used

Code Review

Recommended Mitigation Steps

Consider to define function for client variable.

C4-007 : # Front-runnable Initializers

Impact - Non-Critical

All contract initializers were missing access controls, allowing any user to initialize the contract. By front-running the contract deployers to initialize the contract, the incorrect parameters may be supplied, leaving the contract needing to be redeployed.

Proof of Concept

Navigate to the following contract.

https://github.com/code-423n4/2022-02-aave-lens/blob/aaf6c116345f3647e11a35010f28e3b90e7b4862/contracts/core/CollectNFT.sol#L34

https://github.com/code-423n4/2022-02-aave-lens/blob/aaf6c116345f3647e11a35010f28e3b90e7b4862/contracts/core/FollowNFT.sol#L53

initialize functions does not have access control. They are vulnerable to front-running.

Tools Used

Code Review

Recommended Mitigation Steps

Consider to define function for client variable.

C4-008 : # Missing Re-entrancy Protection

Impact - Non-Critical

Re-entrancy is one of the largest and most significant security issue to consider when developing Smart Contracts. While the EVM cannot run multiple contracts at the same time, a contract calling a different contract pauses the calling contract's execution and memory state until the call returns, at which point execution proceeds normally. This pausing and re-starting can create a vulnerability known as "re-entrancy".

Proof of Concept

Although check effect interaction pattern has been followed, the re-entrancy protection is the best practice.

https://github.com/code-423n4/2022-02-aave-lens/blob/aaf6c116345f3647e11a35010f28e3b90e7b4862/contracts/core/modules/collect/LimitedFeeCollectModule.sol#L154

Tools Used

Code Review

Recommended Mitigation Steps

Consider Implement re-entrancy protection on the related functions.

C4-009 : # DoS With Block Gas Limit

Impact - Non-Critical

When smart contracts are deployed or functions inside them are called, the execution of these actions always requires a certain amount of gas, based of how much computation is needed to complete them. The Ethereum network specifies a block gas limit and the sum of all transactions included in a block can not exceed the threshold.

Programming patterns that are harmless in centralized applications can lead to Denial of Service conditions in smart contracts when the cost of executing a function exceeds the block gas limit. Modifying an array of unknown size, that increases in size over time, can lead to such a Denial of Service condition.

Proof of Concept

Follow the functions shown below.

https://github.com/code-423n4/2022-02-aave-lens/blob/aaf6c116345f3647e11a35010f28e3b90e7b4862/contracts/core/LensHub.sol#L541

Tools Used

Code Review

Recommended Mitigation Steps

Caution is advised when you expect to have large arrays that grow over time. Actions that require looping across the entire data structure should be avoided.

If you absolutely must loop over an array of unknown size, then you should plan for it to potentially take multiple blocks, and therefore require multiple transactions.

code-423n4 / 2022-02-aave-lens-findings

QA Report #73

C4-001 : Use _safeMint() instead of _mint()

Impact - LOW

Proof of Concept

Tools Used

Recommended Mitigation Steps

C4-002 : Critical changes should use two-step procedure

Impact - LOW

Proof of Concept

Tools Used

Recommended Mitigation Steps

C4-003 : Missing zero-address check in constructors and the setter functions

Impact - LOW

Proof of Concept

Tools Used

Recommended Mitigation Steps

C4-004 : Incompatibility With Rebasing/Deflationary/Inflationary tokens

Impact - LOW

Proof of Concept

Tools Used

Recommended Mitigation Steps

C4-005 : Use of Block.timestamp

Impact - Non-Critical

Proof of Concept

Tools Used

Recommended Mitigation Steps

C4-006 : Missing Setter Function On The Client Variable

Impact - Non-Critical

Proof of Concept

Tools Used

Recommended Mitigation Steps

C4-007 : # Front-runnable Initializers

Impact - Non-Critical

Proof of Concept

Tools Used

Recommended Mitigation Steps

C4-008 : # Missing Re-entrancy Protection

Impact - Non-Critical

Proof of Concept

Tools Used

Recommended Mitigation Steps

C4-009 : # DoS With Block Gas Limit

Impact - Non-Critical

Proof of Concept

Tools Used

Recommended Mitigation Steps

C4-001 : Use `_safeMint()` instead of `_mint()`