Aave and CoW Swap Postmortems Conflict After $50M aEth Swap Fails; MEV Extracts Tens of Millions

Aave and CoW Swap published conflicting postmortems after a weekend DeFi failure in which a user attempted to swap about $50.4M of aEthUSDT for aEthAAVE via Aave’s CoW Swap widget and received roughly $36,000. Aave says the user confirmed a 99.9% price-impact warning and blamed illiquid market conditions; it deployed an “Aave Shield” to block swaps with price impacts greater than 25% by default. CoW Swap reported multiple execution faults: a legacy hard-coded 1,200,000 gas validation cap that rejected safer, higher-return quotes; solver execution failures (the optimal solver won but executions failed); and a likely mempool leak that exposed the pending transaction. On-chain analysis shows MEV extraction: a Titan Builder block builder reportedly captured about $34M in ETH for block sequencing, and an MEV bot profited roughly $9.9M via a sandwich attack through a low-liquidity SushiSwap AAVE/WETH pool (~$73k). CoW Swap says an unverified best quote might have returned $5–6M if not for gas cap rejection; it corrected the reported swap fee to $110,368. Neither team fully attributes the actors; both highlight protocol and execution-layer risks: user consent to extreme slippage, mempool visibility, protocol gas/routing limits, solver reliability, and MEV-enabled block-building services. For traders: affected tokens include aEthUSDT and aEthAAVE (AAVE exposure). Expect increased attention to MEV mitigation, tighter default slippage protections, and potential short-term selling pressure or volatility for AAVE and related liquidity tokens. Monitor protocol patches (Aave Shield and CoW Swap gas/routing fixes), on-chain MEV flows, and liquidity depth before executing large swaps.