Symbiosis Bridge Exploit: Hacker Mints 368.9 Billion Synthetic Bitcoin but Cashes Out Only 4.39 WBTC

A cross-chain liquidity protocol known as Symbiosis was exploited on September 11, after an attacker used signed BridgeV2 transactions to mint an enormous quantity of syBTC, a synthetic Bitcoin token designed to represent BTC on other networks. 

Security monitors and crypto news desks reported the activity on BNB Smart Chain, with related token sales later appearing on Ethereum.

According to onchain analysis by Blockaid, transactions routed through BridgeV2 sent roughly \(2^{62}\) raw syBTC units to a newly created externally owned account. With eight decimal places, that figure has been described as about 46.1 billion tokens in some reports. 

A separate alert from DefraudTG put the minted supply higher, at about 368.9 billion syBTC across Ethereum and BNB Chain after eight bridge transactions. The discrepancy likely reflects how different monitors counted raw units, repeated transfers, and tokens remaining on each chain.