TLDR
- On March 12, a trader lost more than $50 million attempting to swap USDT for AAVE through Aave’s user interface — marking DeFi’s largest recorded execution loss.
- While Aave attributed the disaster to market illiquidity, CoW Swap’s investigation uncovered multiple systemic failures, including outdated gas limits that blocked superior pricing quotes.
- The top-performing solver successfully won two consecutive trade auctions yet failed to execute either transaction, forcing the order to settle at the worst available price.
- Evidence suggests a potential mempool leak allowed MEV extraction bots to capture approximately $34 million, while another bot profited nearly $10 million through sandwich attack tactics.
- Aave’s response includes launching “Aave Shield,” an automated system that will reject swaps exceeding 25% price impact.
A devastating transaction occurred on March 12 when an Aave platform user exchanged $50.4 million in aEthUSDT tokens and walked away with merely $36,000 worth of AAVE. The swap was processed via CoW Swap, a decentralized exchange protocol embedded within Aave’s interface.
Post-mortem analyses from both platforms emerged Saturday, March 15. While the teams align on fundamental details, their explanations for how the situation deteriorated differ significantly.
According to Aave, insufficient market liquidity was the primary culprit. The transaction was directed through a SushiSwap liquidity pool containing only $73,000 in total value at that moment.
Before finalizing the swap, the user received a clear alert stating “High price impact (99.9%).” Additionally, they manually selected a checkbox acknowledging potential complete value loss — an action Aave verified through internal records.
Despite these explicit warnings, the transaction proceeded from a mobile device. Aave reports the affected assets remain under custody, and neither team has been contacted by the impacted user.
How CoW Swap’s Infrastructure Made Things Worse
CoW Swap’s investigation revealed significantly more detail, identifying numerous technical breakdowns that amplified what should have been merely a poor trade into a historic catastrophe.
Three solvers submitted responses during the initial quote generation phase. The most favorable quotes would have delivered approximately $5 to $6 million in AAVE tokens — representing a steep 90% loss, yet dramatically superior to the final outcome.
Unfortunately, CoW Swap’s quote validation infrastructure relied on a fixed gas limit of 12 million units. The platform characterized this as “legacy code predating current gas consumption patterns.” Superior pricing routes exceeded this threshold and were automatically disqualified.
A single quote survived validation — from a solver proposing roughly 329 AAVE, performing 150 to 200 times worse than rejected alternatives. This quote established the order’s limit price.
Another solver, designated as Solver E, identified a superior route and secured victories in two sequential trade auctions. Yet it never broadcast either transaction on-chain. Following two consecutive failures, it ceased participating entirely. CoW acknowledged its monitoring systems lacked capabilities to detect or flag such behavioral patterns.
MEV Bots and a Possible Mempool Leak
With only an inferior solver remaining active, conditions became ideal for exploitation. Blockchain records indicate block builder Titan Builder extracted approximately $34 million in ETH from the transaction. Separately, an MEV bot captured nearly $10 million through sandwich attack execution.
CoW Swap identified potential evidence of mempool information leakage. Despite submitting the transaction through private channels, Etherscan metadata suggested it surfaced in the public mempool prior to block inclusion. This investigation remains active.
CoW Swap’s integration with Aave had been promoted partially on MEV-protection features when the partnership expanded in December 2025.
Aave is implementing Aave Shield, which will automatically reject swaps generating price impact exceeding 25% by default. CoW Swap confirmed the hardcoded gas limit has been corrected. This incident followed just two days after a separate Aave oracle malfunction that caused $26 million in improper liquidations affecting 34 accounts.
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