Summary

Storage collision because between ThunderLoan and ThunderLoanUpgraded could cause conflicts and override sensible variables

Vulnerability Details

In this case, the first implementation of the logic contract stores uint256 private s_feePrecision at the first storage slot and an upgraded logic contract stores uint256 private s_flashLoanFee; at the same first slot. When the updated logic contract attempts to write to the s_flashLoanFee variable, it will be using the same storage position where the previous value for s_feePrecision was being stored, and overwrite it. This is due to deleting s_feePrecision and adding FEE_PRECISION on the updated version.

Impact

High

Tools Used

Manual Analysis

Recommendations

By following Openzeppelin guidelines we need to have new versions of a logic contract extend previous versions.
section "Storage Collisions Between Implementation Versions"
https://docs.openzeppelin.com/upgrades-plugins/1.x/proxies