Cross-chain protocol Symbiosis has said it reclaimed about 15 bitcoin after a vulnerability in its native Bitcoin Bridge was used on September 11. The team also extended a 20 percent white-hat bounty to the attacker, with a September 13 cutoff for a direct return of funds.
In an official update, the project said the incident began around 04:28 UTC.
An attacker exploited a weakness in the Bitcoin Bridge, after which native BTC routes were stopped.
Symbiosis stressed that the problem was limited to that bridge. The component was separated from the rest of the system.
Routes on EVM networks, TRON, TON, and other supported paths kept running, as did Octopools and remaining protocol pieces.
The relayer group also continued operating.
Later the same day, bitcoin swaps were restored through partner rails on Chainflip and THORChain.
The protocol’s own Bitcoin Bridge stayed paused pending further review.Symbiosis reported that roughly 15 BTC had been recovered and placed in a team-controlled multisignature wallet.
The project said it had reached the attacker with an offer equal to 20 percent of the funds, open through September 13, 2026.
Symbiosis experienced a security incident. At approximately 04:28 UTC on Sep 11, 2026, attacker exploited a vulnerability in Bitcoin Bridge. BTC routes have been halted. Other routes remain operational and safe.
Where we stand:
• Only the Bitcoin Bridge was affected, and it is…— Symbiosis (@symbiosis_fi) September 11, 2026
After that window, the same 20 percent would be available to anyone who supplied information that led to additional recovery.
Final loss figures were still being calculated, the team said, with confirmed numbers promised in a later update.
Liquidity providers were being contacted individually, and a compensation framework was under construction, with criteria to be published soon.
Independent monitoring by Blockaid described a signed BridgeV2 receive call that minted on the order of 2^62 raw syBTC units on BNB Chain—about 46.1 billion tokens at eight decimals—sent to a newly created wallet.
The same party later sold about 4.39 WBTC on Uniswap v4 on Ethereum, realizing roughly $336,000.
The gap between the enormous mint and the much smaller cash-out reflects how quickly the bridge was isolated and how little liquid demand existed for the unbacked tokens.
As of mid-September, the native Bitcoin Bridge remained offline.
A full technical post-mortem and a published LP compensation plan had not yet appeared.
Symbiosis thanked researchers who moved quickly and said it would keep posting updates.
The case is another reminder of how bridge designs that mint synthetic bitcoin can fail when a receive path is abused.
Here the headline token amount was vast, but realized proceeds and the protocol’s reported recovery of 15 BTC were far smaller. Users waiting on the native route still face a pause until the team finishes accounting and decides how to bring that path back.