Introduction
Security auditing in DeFi isn't just about reading code; it's about understanding architectural intent. Recently, I decided to build my personal audit portfolio by diving into the Monetrix V1 codebase. This journey taught me that sometimes what looks like a critical bug is actually a design feature, and sometimes a simple order of operations can lead to user fund loss.
In this post, I want to share two key findings from my analysis.
Case 1: The "Surplus Bug" β When Architecture Meets Misunderstanding
During my audit, I encountered a report suggesting a bug in the distributableSurplus calculation. The claim was that the protocol failed to decrement the surplus variable after minting yield.
The Initial Hypothesis: The contract was caching the surplus and failing to update it after mint().
The Audit Reality: After deep-diving into the MonetrixAccountant.sol logic, I realized the protocol employs a dynamic state calculation:
Solidity
function surplus() public view returns (int256) {
return totalBackingSigned() - int256(usdm.totalSupply());
}
Because the system relies on totalSupply() as the source of truth, the surplus updates automatically whenever tokens are minted.
Lesson: Always check if the state is cached or computed dynamically before flagging it as a state-inconsistency bug.
Case 2: Withdrawal Security β The CEI Pattern
I audited the withdrawal flow in MonetrixVault.sol, specifically the claimRedeem function.
The Vulnerability: The function executes usdm.burn() before interacting with the RedeemEscrow contract.
Solidity
usdm.burn(amount);
IRedeemEscrow(redeemEscrow).payOut(msg.sender, amount);
The Risk: If the payOut external call fails (due to unexpected conditions), the user's tokens are burned, but they never receive the underlying USDC. This is a clear violation of the Checks-Effects-Interactions (CEI) pattern.
Recommendation: The protocol should prioritize the external interaction (or ensure atomicity) to prevent permanent loss of user funds.
Final Thoughts
Building a portfolio isn't just about finding "Critical" bugsβit's about demonstrating your ability to reason about complex systems. You can check my full analysis and PoCs in my Monetrix-audit GitHub repository.
Have you encountered similar architecture vs. bug discussions? Let's discuss in the comments!
https://github.com/rdin777/Monetrix-audit
Top comments (0)