On November 3, 2025, the decentralized finance protocol Balancer (via its V2 smart-contract system) was exploited across multiple blockchains, resulting in total estimated losses of around US $128 million.
The attack appears to have arisen from a flaw in Balancer V2’s vault/authorization logic that allowed the attacker to siphon assets such as WETH, osETH and wstETH from linked liquidity pools.
The exploit took place on Ethereum and several layer-2/side chains (including Arbitrum, Base, Optimism, Polygon and others) due to Balancer’s composable/multi-chain architecture. In response, the Balancer team confirmed the issue, launched an investigation, and many users and protocols began withdrawing funds to avoid further loss.
The incident is regarded as one of the largest DeFi breaches of 2025, and it highlights how even audited, well-known protocols remain vulnerable to complex composability and smart-contract risks.
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