MEV Bot Sandwich Attack Drains $50M Swap to $36K

A crypto user turned $50.4 million into $36,000 Thursday. An Ethereum MEV bot sandwich attack drained the rest.

The mev bot sandwich attack netted nearly $10 million as a recently funded wallet from Binance attempted to swap $50.4 million USDT into AAVE tokens via CoW Protocol and SushiSwap. The user received 327 AAVE tokens worth approximately $36,000. That’s a 99.93% loss.

The math is brutal. User paid $154,000 per AAVE. Market price: $114. The bot saw the massive order coming and moved first.

**How the MEV Bot Sandwich Attack Worked**

MEV bots scan pending blockchain transactions looking for profitable opportunities. This one spotted the $50 million AAVE order before it executed.

The mev bot sandwich attack worked by flash-borrowing $29 million in wrapped ETH from Morpho. It used those funds to buy AAVE on Bancor, driving the price up ahead of the user’s order. When the user’s transaction executed on SushiSwap at the inflated price, the bot immediately sold its AAVE holdings back into the market.

Profit: $9.9 million. Execution time: seconds.

The technique is called a “sandwich attack” because the bot places one transaction before and one after the victim’s trade. The user gets squeezed in the middle, paying inflated prices while the bot extracts value from both sides of the trade.

**The User Saw Warnings**

This wasn’t a silent failure. The interface showed warnings.

Aave founder Stani Kulechov explained that the protocol warned the user about “extraordinary slippage” due to the “unusually large size of the single order.” The user confirmed the warning on a mobile device and proceeded anyway, accepting the high slippage.

CoW DAO echoed this on X: “Despite clear warnings that showed the user they would lose nearly all of the value of their transaction, and despite needing to explicitly opt into the trade after seeing the warning, the user chose to proceed with their swap.”

Question is why someone would confirm a warning showing a 99.93% loss.

Automated market makers like SushiSwap adjust slippage based on pool depth and trade size. A $50 million order in a relatively small liquidity pool creates massive slippage. The formula is predictable. The outcome was visible before execution.

**No Pool Could Handle This**

CoW DAO was blunt: “No DEX, DEX aggregator, public liquidity pool, or private liquidity pool (or combination thereof) would have been able to fill this trade at anywhere near a reasonable price.”

The order was too large for available liquidity. Splitting into smaller trades over time would have reduced slippage significantly. Executing the full amount in one transaction guaranteed catastrophic losses even without MEV extraction.

This mev bot sandwich attack highlights a fundamental DeFi problem: interface warnings don’t prevent execution. Users can override any guardrail if they choose to proceed.

**Protocol Response**

Aave and CoW Protocol both offered to return fees collected from the transaction.

Kulechov said Aave would attempt to contact the user to return $600,000 in fees collected. CoW DAO said it would refund any protocol fees associated with the transaction.

The MEV bot kept its $9.9 million. That’s not recoverable.

Kulechov noted that “while DeFi should remain open and permissionless, allowing users to perform transactions freely, there are additional guardrails the industry can build to better protect users.”

CoW DAO admitted that trades like this “show that DeFi UX still isn’t where it needs to be to protect all users.”

**MEV Extraction Remains Unsolved**

MEV bots operate in a legal gray area. They extract value from user transactions by manipulating transaction ordering. The practice is widespread across Ethereum and other chains.

Ethereum co-founder Vitalik Buterin has proposed solutions to reduce MEV impact, including encrypted mempools and protocol-level protections. None are implemented at scale yet.

For now, large traders face a choice: accept MEV extraction or use private transaction channels that bypass public mempools. Neither option is ideal. One costs money, the other costs decentralization.

The user lost $50 million to slippage and MEV combined. The bot made $10 million in seconds. Warnings were shown and ignored. The transaction executed exactly as the interface predicted.

That’s DeFi working as designed—and the problem.