Balancer pins $116.6M multi-chain exploit on rounding bug in swap "upscale" function; recovery and pool pauses underway

first published 2025-11-06T13:54:40Z

Balancer traced the Nov. 3 exploit to a rounding bug in its "upscale" function used during swaps, which attackers abused to manipulate pool balances and siphon funds before withdrawing. The breach drained $116.6M across Ethereum, Arbitrum, Base and Polygon (notably 6,587 WETH, 6,851 osETH and 4,260 wstETH). StakeWise recovered ~$19M (≈73.5%) of osETH for users. Mitigations: affected pools paused, new pool creation and rewards halted, partners blocked/froze assets, whitehats reclaimed some funds; a final reconciled report will be published after verifications.

AI Analysis

The exploit was caused by a concrete rounding-bug in the protocol's "upscale" swap function that allowed manipulation of pool balances and removal of funds; $116.6M was drained across multiple chains and large token quantities were taken. Recovery actions (paused pools, halted new pools/rewards, partner freezes, whitehat recoveries and StakeWise reclaiming ~$19M osETH) are ongoing, indicating material short-term risk to Balancer liquidity and user funds.

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