Syscoin pauses bridge after attacker minted 5B SYS

Syscoin paused its cross-chain bridge after an attacker exploited a validation bug to create roughly 5 billion unauthorized SYS on the project’s UTXO chain. The newly minted tokens first went to a single address and were later spent and split into two wallets holding about 4 billion and 1 billion SYS.

The incident involved the bridge’s relay path, which verifies cryptographic proofs for transactions moving between chains. The relay path accepted an invalid transaction proof and the system treated the fraudulent transfer as valid, producing an unauthorized UTXO output of roughly 5 billion SYS.

Syscoin paused the bridge while tracing the illicit tokens and coordinating with exchanges and custodians to block the tainted balances from entering open markets. The team asked users not to interact with the bridge while it remains offline.

Syscoin wrote in an update: “An attacker exploited a validation issue in the bridge flow that resulted in an unauthorized SYS output being created on the UTXO side. The team has identified the affected validation path and has a fix in place. Our priority now is to complete implementation and review of the fix, while also determining the correct process to rectify the unauthorized SYS output and neutralize its impact on the network. We will provide further updates once the remediation path has been finalized.”

The project did not provide a timetable for completing the fix or for any token recovery steps. It said the response will include applying the patch, an internal review, tracing the unauthorized output and measures to limit harm to users and markets.

Bridge implementations depend on accurate validation of proofs; if a relay path accepts an invalid proof, an attacker can create or move assets that should not exist on the target chain. A blockchain security tracker recorded 40 major incidents in May 2026, including eight bridge and cross-chain exploits.

Syscoin said it will issue further updates once the remediation plan is finalized.