code423n4 commented 1 year ago

Lines of code

https://github.com/code-423n4/2023-07-amphora/blob/daae020331404647c661ab534d20093c875483e1/core/solidity/contracts/core/Vault.sol#L1

Vulnerability details

Impact

For upgradeable contracts, there must be storage gap to "allow developers to freely add new state variables in the future without compromising the storage compatibility with existing deployments" (quote OpenZeppelin). Otherwise it may be very difficult to write new implementation code. Without storage gap, the variable in child contract might be overwritten by the upgraded base contract if new variables are added to the base contract. This could have unintended and very serious consequences to the child contracts, potentially causing loss of user fund or cause the contract to malfunction completely.

Refer to the bottom part of this article: https://docs.openzeppelin.com/upgrades-plugins/1.x/writing-upgradeable

Proof of Concept

following contract is intended to be upgradeable in the code base.

vault.sol

However, it doesn't contain storage gap. The storage gap is essential for upgradeable contract because "It allows us to freely add new state variables in the future without compromising the storage compatibility with existing deployments". Refer to the bottom part of this article:

https://docs.openzeppelin.com/contracts/3.x/upgradeable

If the contract inheriting the base contract contains additional variable, then the base contract cannot be upgraded to include any additional variable, because it would overwrite the variable declared in its child contract. This greatly limits contract upgradeability.

## Tools Used
Manual review

## Recommended Mitigation Steps
Recommend adding appropriate storage gap at the end of upgradeable contracts such as the below. Please reference OpenZeppelin upgradeable contract templates.
```solidity
uint256[50] private __gap;