Coldcard Exploit Highlights Flaws in Air-Gapped Wallet Security
A recent exploit of Coldcard hardware wallets has raised concerns about air-gapped Bitcoin wallet security. The issue stems from weak seed-generation entropy, which allowed attackers to compromise private keys.
Coldcard's company, Coinkite, issued a security advisory on July 30, warning that seeds generated on affected firmware versions (4.0.1 through 4.1.9) are at risk if they were created without at least 50 independent private dice rolls and without a strong BIP-39 passphrase.
The technical root cause was detailed by Block's Bitcoin engineering team, which found that the vulnerable firmware caused libngu.random to fall back to MicroPython's deterministic Yasmarang generator instead of the STM32 hardware RNG. This resulted in seed creation becoming a reproducible software-randomness problem.
CoinKite says fixed firmware is now available for affected models, but updating firmware does not repair seeds that were already generated on vulnerable firmware. Users with at-risk seeds must move funds to a newly generated wallet rather than simply patching the device.