Syscoin paused its cross-chain bridge after an attacker exploited a validation flaw to mint roughly 5 billion unauthorized SYS tokens on the UTXO chain. The project is tracing the funds and coordinating with exchanges to block the tainted balances from entering open markets.
Syscoin halted its cross-chain bridge after an attacker exploited a validation flaw to mint roughly 5 billion unauthorized SYS tokens on the network's UTXO chain, the project said June 7.
"An attacker exploited a validation issue in the bridge flow that resulted in an unauthorized SYS output being created on the UTXO side," Syscoin said in a statement.
The exploit targeted the bridge relay path, which validates transactions moving between chains. The system wrongly accepted a fraudulent transaction proof, minting the unauthorized output through the UTXO bridge path. The funds initially landed in a single address before the attacker split them into two tainted balances of roughly 4 billion and 1 billion SYS across separate wallets.
The project is tracing the unauthorized tokens and coordinating with exchanges to prevent the tainted balances from entering open markets. Syscoin said it 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," the team said.
SYS fell more than 7% in 24 hours to trade near $0.0016, according to BeInCrypto Markets data, even as the broader crypto market capitalization rose more than 2%. The token's decline reflects concerns over potential dilution from the unauthorized mint, which represents a significant portion of Syscoin's total supply.
The incident adds to a growing tally of cross-chain security failures. Security firm PeckShield logged 40 major incidents in May 2026, including eight bridge and cross-chain exploits. Bridges remain a prime target for attackers due to their complex codebases and the large pools of value they manage across multiple chains.
Syscoin urged users not to interact with the bridge while it remains paused. The project said it will provide further updates once the remediation path has been finalized.
This article is for informational purposes only and does not constitute investment advice.
