Syscoin releases a technical review stating that on June 7th, its UTXO-to-NEVM cross-chain bridge experienced a malicious UTXO destruction transaction that created asset ambiguity, causing the bridge contract on the NEVM side to incorrectly release 5 billion native SYS tokens.

The vulnerability stemmed from inconsistent cross-layer interpretation of the same transaction between Syscoin Core and the NEVM relay: Core recognized it as a attacker-defined asset, while the relay interpreted it as native SYS.
Syscoin states that after tracking the flow of funds and contacting the attacker through on-chain information, the 5 billion SYS tokens have been returned to the official recovery address, and subsequently destroyed via a standard OP_RETURN transaction, preventing the protocol from spending them, restoring the supply to the expected level.
The cross-chain bridge remains suspended, and the team has fixed the relay logic to reject multi-assets, duplicate asset commitments, or any proof of asset destruction with unclear asset identity.