Uniswap Pool 'Toxic' Fee Trap Swallows $130k in 29 Hours

A Uniswap v4 pool on BNB Chain processed over $130,000 in fees between August 22 and 23, 2026, without users realizing they were being charged a 12.8% liquidity provider fee. The pool displayed a 0% fee in aggregator quotes, but executed the higher rate when trades were made.

The discrepancy was due to a dynamic fee function that used three layers of determination to calculate fees. The first layer checked if the caller was one of three specific addresses, and if so, returned a 0% fallback tier. However, this layer could be bypassed by specifying a normal address.

The second layer checked gas levels, which were high in aggregator quotes but had already been consumed by the Router and other nodes before real transactions reached the pool. This meant that even with a normal address, the fee was still 0% for quote simulations.

Real transactions that passed these two layers entered the third layer, where the block environment fingerprint was hashed and used to determine the fee tier. The current configuration had three tiers: 8%, 10%, and 10%, with a fallback to 0% if no tier was hit. However, in this case, the effective rate at the time of the sample transaction's execution was 12.8%.