Trader Loses $1.8M to Same-Block Backrun on DEX

A trader who swapped 1,126.44 ETH (about $2.01 million) on Monday at 01:59 UTC received roughly $14,500 in tokens after the order was routed through a low-liquidity pool and a block builder captured approximately $1.8 million in same-block arbitrage, according to GoPlus Security.

The 0x router sent the trade into an AVAIL/WETH pool on Uniswap v3 that held little liquidity. The swap pushed about 1,117 ETH into that pool and executed at prices roughly 120 times higher than the price at which AVAIL could later be sold, producing nearly 6.67 million AVAIL tokens credited to the trader at an inflated internal price, according to GoPlus Security.

After the initial trade, the router sold a small amount of externally sourced AVAIL into the same pool to extract about 1,072 WETH. The block builder identified as Titan Builder received approximately 1,018 ETH, about $1.8 million, as the builder reward from the same-block arbitrage. The AVAIL tokens obtained by the trader were later swapped for Lighter (LIT) tokens worth about $14,200, a roughly 99.3% loss on the position.

GoPlus Security described the incident as “a textbook case of same-block backrun extraction,” and noted it differed from a classic sandwich attack because the main profit came from a highly imbalanced backrun arbitrage.

Trader Ruslan Khairullin warned: ‘This is what happens when you clicked confirm faster than you read the route. Painful lesson to see in a real time.’

Data from DefiLlama shows Titan Builder’s block-building services have generated $112.6 million in revenue so far this year, with the firm’s largest single-day extraction occurring in March at about $34 million. Requests for comment to Titan did not receive an immediate response.

The mechanics in this case show how a routing decision can push a large swap into a low-liquidity pool, causing the swap to execute at an inflated internal price. Same-block actors can then execute complementary trades within the same block to capture the price difference before the original trade settles at market prices.

Traders are advised to inspect transaction routes and slippage settings before confirming swaps and to be cautious of routes that pass through unusually low-liquidity pools.