On May 20, 2026, RetoSwap (Haveno fork on Monero) failed to verify ACK message sources. Attackers registered attacker-controlled addresses as arbitrators for multisig wallets, stealing $2.7M from traders.

RetoSwap (a Tor-based P2P multisig DEX powered by the Haveno trade protocol for trading Monero) was actively exploited. Attackers sent fake, out-of-order ACK messages impersonating the arbitrator during ongoing trades. This tricked the client into updating the arbitrator’s node address to the attacker’s controlled address, allowing them to create a compromised multisig wallet before the victim deposited funds. The exploit mainly affected crypto-to-crypto trades. RetoSwap immediately banned the attacker’s onion address, forced a client version update to halt all trading, and is working on a patch and potential recovery for affected users. Approximately 7,000 XMR were stolen.