BALANCER BLAMES ROUNDING ERROR FOR $128M MULTI-CHAIN EXPLOIT
Balancer has identified a rounding flaw in its swap logic as the root cause of the November 3 exploit that drained over $128 million from its Composable Stable Pools (CSPs) across multiple chains, including Ethereum, Base, Arbitrum, Avalanche, and Polygon. The issue stemmed from a rounding error in the upscale function for EXACT_OUT swaps within the v2 vault's batchSwap feature, which attackers used to manipulate pool balances and siphon liquidity. Emergency response teams like Hypernative, SEAL 911, StakeWise DAO, and BitFinding helped recover portions of the stolen funds, with StakeWise DAO retrieving 73.5% of osETH losses. The exploit primarily affected v5 CSPs, while v6 pools were automatically paused, and Balancer v3 remains unaffected.