RetoSwap loses about 7,000 Monero to forged arbitrator messages in Haveno; trading suspended again in June
An authentication flaw in Haveno, the protocol under Monero exchange RetoSwap, let an attacker pose as the arbitrator and take about 7,000 XMR (US$2.7M) on 20 May 2026. No recovery reported. Trading was suspended again on 17 June. Don't trade there until it relaunches.
If you use RetoSwap or another Haveno-based exchange, stop trading and keep your local wallet backup until the operators publish a tested fix. Use only an updated client when trading restarts.
What’s happening
On 20 May 2026 an attacker stole about 7,000 Monero (roughly US$2.7 million) from traders on RetoSwap, a peer-to-peer exchange built on the open-source Haveno protocol. The flaw was in Haveno, not RetoSwap's own servers. Haveno accepted a forged, out-of-order acknowledgement message and overwrote the arbitrator's stored network address with one the attacker controlled. That put the attacker in the shared multisignature wallet before either trader deposited funds. Losses fell on large crypto-to-crypto trades, and fiat trades were reported unaffected. RetoSwap halted trading within minutes by raising the minimum client version to 2.0.0 and blocking the attacker's address. The Haveno project opened a fix the same day. It checks the sender against a known public key and stops address changes before the wallet exists. BlockSec does not say whether it was merged or released. On 17 June RetoSwap suspended trading again, saying Haveno was being exploited a second time. Losses from that were still being assessed. Monero cannot be traced or frozen, and no recovery has been reported. Whether trading has resumed is not known.
- What
- Breach
- Affects
- RetoSwap and the Haveno decentralised Monero trading protocol
- Affected
- Haveno trading protocol (message handling dating to a March 2025 commit, per Halborn as cited by iToken)
RetoSwap clients below version 2.0.0 - Fixed in
- No fix yet
- Since
- 20 May 2026
- Closed
- 17 June 2026
Timeline
- Wider attacksPartly fixed
RetoSwap suspended trading again after saying the Haveno protocol was being actively exploited a second time. Losses were still being assessed, trading stayed suspended with no restart date, and RetoSwap said it was weighing options to help affected traders.
- New fixPartly fixed
The Haveno project opened a pull request titled 'core: refuse to update node address before multisig created'. It checks the sender against the peer's known public key and blocks address changes until the multisig wallet exists. BlockSec does not say whether it was merged or released.
- Made publicPartly fixed
RetoSwap traders lost about 7,000 XMR (roughly US$2.7 million) after an attacker sent a forged acknowledgement message that appeared to come from the arbitrator. Haveno's lead developer reported active exploitation, and RetoSwap halted trading by raising its minimum client version to 2.0.0 and blocking the attacker's onion address.
Sources
- Web3 security roundup: Verus bridge, RetoSwap and moreBlockSec · 21 May 2026
- RetoSwap hack tracker entryiToken · 21 May 2026
- RetoSwap Suspends Trading Again: Haveno Protocol Exploit TwiceCoinGabbar · 17 June 2026