Corn

The Challenge

The protocol's core complexity lay in the interaction between three operations: depositing assets into the vault, staking those deposits for yield, and distributing rewards across depositors. The share pricing mechanism needed to correctly account for rewards in the conversion between assets and shares. Any miscalculation in this conversion could allow depositors to extract more value than the vault contains, leading to insolvency for remaining depositors. The combination of these operations in arbitrary order created a state space too large for manual analysis.

Our Approach

Solvency invariants were defined requiring that the vault's total assets must always be greater than or equal to the value owed to all shareholders. The fuzzer generated randomized sequences of deposits with varying amounts, withdrawals of partial and full positions, and reward distributions at different intervals. Handler functions simulated multiple users interacting simultaneously to test share pricing under concurrent access. Properties were checked after every operation to catch the earliest point at which accounting diverged.

Findings

Results

The critical insolvency bug was identified in the share minting logic — new deposits received slightly more shares than they deserved when rewards had recently been distributed, because the conversion rounded in favor of the depositor rather than the protocol. Over time, this would drain the vault. The fix reversed the rounding direction, and continued fuzzing confirmed the fix held across millions of additional test sequences. The Corn cofounder praised Recon's work in making invariant testing accessible and practical for their development workflow.