Coldcard Wallet Attacks Enter Fourth Wave, Putting 449 BTC at Risk

A suspected fourth wave of attacks targeting vulnerable Coldcard-generated Bitcoin wallets may already be underway, with blockchain researcher Alex Thorn warning on August 3 that almost 449 BTC had been swept from hundreds of addresses in about two and a half hours.

The latest activity, which was still unfolding as Thorn posted, follows three earlier waves that researchers have linked to the same weak-entropy vulnerability affecting certain Coldcard firmware versions.

New Sweeps Continue

Thorn said his latest analysis had identified 218 transactions affecting 462 suspected victim addresses between Bitcoin blocks 960778 and 969792. The transactions moved 388.93 BTC, valued at about $24.4 million at current rates, into 216 destination addresses, almost all of which had been just created and had no past transaction history.

“These are LIKELY Coldcard victims — they match the shape of coldcard vulnerable utxos and the elevated transaction pattern gives me high confidence they are another wave of attack,” he wrote.

The analyst stressed that he had no direct confirmation from victims yet, which is why he had deliberately used “likely” out of caution. He also quickly corrected the destination list, removing six addresses, which he said had already been receiving and spending BTC way before the Coldcard incident started on July 30. The six accounted for just over 5 BTC of the figure previously calculated.

Furthermore, Thorn stripped out 89 multisig addresses from his list, since none had appeared in the first three waves, taking the surviving core to 709 addresses and 448.73 ($28.1 million) across both confirmed and still-pending transactions.

He urged users to immediately move their funds off affected Coldcard devices and use higher transaction fees, and also warned that some of the pending transactions had Replace-by-Fee, or RBF, enabled, meaning that victims whose transactions were still sitting in the mempool might have a very brief chance to outbid the attacker and reclaim their funds before confirmation.

Earlier Waves Still Unspent

Galaxy Research has estimated that the first three confirmed waves drained 1,367 BTC, valued at around $85.7 million, from 4,585 Bitcoin addresses. According to the firm, those funds have not been spent and are still in attacker-controlled wallets, suggesting a coordinated operation rather than opportunistic theft.

However, not every stolen BTC has stayed put. One victim holding close to 30 BTC had 17 of them routed through ThorChain into the Duel online casino, which reportedly told the victim to file a police report before it could consider a freeze.

The attack stems from a vulnerability affecting seeds generated on certain Coldcard firmware versions released after March 2021. Coinkite, the maker of the Coldcard wallet, confirmed that seeds created on affected Mk3, Mk4, Mk5 and Q devices are exposed, and although newer patched firmware has stopped the problem for future seeds, it cannot secure old ones. It also said that it has destroyed all remaining vulnerable inventory, halted shipments, and is working with customers and law enforcement as they try to identify those responsible for the theft.

In addition, the firm advised users to immediately migrate to a new seed on an unaffected device, with Thorn pointing out that every single-signature Coldcard address generated under the vulnerable conditions will eventually get drained.

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