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Bitcoin swept from thousands of Coldcard wallets as new wave targets small balances

Galaxy Research said the third wave drained about 208 bitcoin from 1,912 addresses between Friday midday and Saturday morning UTC, using more complex onchain patterns than earlier attacks.

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A vulnerability in a March 2021 Coldcard firmware release has enabled attackers to systematically drain bitcoin by reproducing keys generated with weak software-based randomness, and a third wave of sweeps is now spreading to more wallet addresses, according to analysis by Galaxy Research published by CoinDesk.

The observed thefts total 1,367 bitcoin, nearly $89 million at recent prices, pulled from 4,585 addresses across three distinct attack waves. CoinDesk reported that the latest wave is targeting smaller balances, with attackers sweeping wallets worth a few thousand dollars each and draining roughly 208 bitcoin from 1,912 addresses between Friday midday and Saturday morning UTC.

Galaxy Research said each wave appears to be the work of a single operator, though it cannot prove whether the same attacker is behind all three because blockchain data does not show coordination between separate sweeps. CoinDesk added that wave three differs from earlier activity by sending each victim’s coins to its own destination instead of the shared collector addresses that were easier to trace, and by parking funds in pay-to-witness-script-hash outputs that can support multisignature or timelock conditions.

CoinDesk also noted that wave three batched an average of six victims into each sweep, while the July 30 opening wave averaged close to a full coin, 1,083 bitcoin from 1,196 addresses, in about 41 minutes. The underlying flaw traces to seed generation being routed to a predictable software randomizer rather than the chip’s hardware one, leaving a bounded set of possible keys that can be reproduced offline after disclosure and enough compute.

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