According to Wu Blockchain, Balancer mentioned in its preliminary incident report that the attack stemmed from the rounding-down logic in the upscale function of V2 Composable Stable Pools under the EXACT_OUT path. When the scaling factor is a non-integer, the function generates exploitable precision errors. The attacker leveraged the deferred settlement mechanism of batchSwap (which allows temporary borrowing of assets during a transaction and returning them at the end), along with the design where BPT is treated as a regular token, bypassing the minimum pool share restriction. This caused the pool liquidity to drop to extremely low levels, enabling manipulation of pool balances and extraction of funds. https://www.(wublock123.com)/index.php?m=content&c=index&a=show&catid=6&id=51393