Symbiosis recovers 15 BTC after Bitcoin Bridge exploit

Symbiosis, a cross‑chain liquidity protocol, announced the recovery of roughly 15 BTC following a security incident that targeted its native Bitcoin Bridge on September 11. The exploit allowed an attacker to mint billions of synthetic BTC tokens (syBTC) but resulted in the sale of only a small portion of the value.

Details of the exploit

Security firm Blockaid reported that the attacker called the BridgeV2 contract on BNB Chain, creating about 46.1 billion unbacked syBTC. The amount represents more than 2,000 times Bitcoin’s fixed supply of 21 million coins, but the synthetic tokens were not actual BTC on the Bitcoin network.

Through Uniswap v4 on Ethereum, the attacker managed to sell approximately 4.39 WBTC, generating around $336,000. DeFiLlama classified the loss as an “unbacked cross‑chain mint” of the same dollar value.

Recovery and bounty offers

Symbiosis moved the recovered 15 BTC to a team‑controlled multisig wallet. Initially, the protocol offered a 20 % bounty to the attacker for returning the remaining funds by September 13. After that deadline, the same bounty percentage will be offered to anyone who provides information leading to further recovery.

Impact on services

The native Bitcoin Bridge remains paused, while routes involving EVM networks, TRON, and TON continue to operate. The Octopools product and relayer network stayed online throughout the response.

Bitcoin swaps are now available through third‑party integrations with Chainflip and THORChain, giving users an alternative while Symbiosis works on restoring its own bridge.

Compensation for liquidity providers

Symbiosis is contacting affected liquidity providers directly and is preparing a compensation framework. Eligibility criteria have not yet been published, and the final loss figure is still being calculated.

Context of similar incidents

• Blockstream’s Liquid Network suffered a similar unbacked mint of ~4,000 L‑BTC, with most of the funds later returned.
• Hyperbridge experienced an unauthorized mint of ~1 billion DOT‑equivalent tokens, extracting about $237,000.
• The Sandbox’s bridge vulnerability led to the mint of ~14.75 million SAND, generating roughly $675,000.