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Coldcard Bitcoin heist topped $70 million as attackers used provider tools

The attack exploited a Coldcard firmware issue, and experts said holders of funds in single-signature Coldcard addresses should move to secure custody.

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A Coldcard-related Bitcoin theft has already surpassed $70 million after an attack that exploited a fault in the wallet device, according to Bitcoin Magazine. The outlet also cited experts saying the attacker used a paid account at a well-known blockchain-services provider to query source addresses during sweep activity.

Bitcoin Magazine said Block engineer Clay Garrett reported an unusual pattern in sweeps that led to the hypothesis that the operator used provider tools, and that authorities were notified. Galaxy Digital’s research arm also posted that the moving pattern suggests the same attacker, while noting it does not show the attack mechanism itself, which can resemble a legitimate coin owner sweep.

The report added that Coinkite linked earlier thefts to a Coldcard Mk3 firmware bug, starting with version 4.0.1 in March 2021, that caused seed generation to fall back to a weaker software pseudorandom number generator instead of hardware true randomness. Coinkite said this made private keys for many single-signature wallets more predictable, enabling attackers to brute-force, especially where wallets were created without dice rolls or a strong BIP-39 passphrase.

Bitcoin Magazine further reported that after Coinkite disclosed that all its models were vulnerable following additional thefts, engineers warned that more Bitcoin addresses could be at risk. It said Bitcoiners should move funds out of single-signature Coldcard addresses into secure custody.

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