EMERGENCY BITCOIN UPDATE: Coldcard Attack Explained | Rob Hamilton
7/31/2026 · 42 min · transcript via whisper
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Key topics
— Coldcard firmware bug introduced in early 2021 affects MK3, MK4, MK5, and Q models. A one-line code error prevented proper entropy generation during seed phrase creation, reducing randomness from 2^256 to as low as 2^32 bits on MK3 devices.
— Immediate threat: Attackers have already begun brute-forcing all possible seed phrase combinations. Single-signature wallets without passphrases or user-generated entropy are being actively drained. Estimated losses already exceed 1,000 BTC and growing.
— Multisig exposure: Even multisig wallets are at risk if majority signers use vulnerable Coldcards. Two-of-three and N-of-N configurations using only Coldcards are vulnerable once attackers identify the key combinations on-chain.
— Protection methods: Passphrases (25th word), dice-rolled entropy, or user-provided randomness added during setup can mitigate risk. Firmware updates for MK4/MK5/Q add 45–50 bits entropy but remain vulnerable to well-resourced attackers.
— Not a broader ecosystem issue: Trezor, Foundation, and other hardware wallets were unaffected. This vulnerability is specific to Coldcard's implementation of the entropy library.
— AI's role: Open-source LLM models without safety guardrails (e.g., Kimi K3) made the bug discoverable. The initial attacker was amateur; sophisticated actors are now escalating efforts with GPU farms.
Market & price signals
— None discussed.
Actionable insights
— Immediate action required for anyone who generated seed phrases on a Coldcard MK3, MK4, MK5, or Q without a strong passphrase or user entropy: move funds within 24 hours to a new secure wallet (hardware wallet, Swan Vault, Casa, Unchained, or temporarily to an exchange with proof of reserves like River).
— Multisig users with only Coldcard signers should migrate funds urgently. Those in a 2-of-3 setup with non-Coldcard devices (Ledger, Trezor) are safer but should still monitor. Consider Mara Slipstream for mainnet broadcasting if majority signers are vulnerable Coldcards.
— Passphrase strategy: Single-signature with a genuinely strong passphrase (12+ random words) functions as effective 2-of-2 security; moving to multisig is now simpler and may reduce user error risk compared to complex passphrase management.
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