A critical firmware bug in Coldcard hardware wallets has enabled attackers to drain 594.48 Bitcoin — worth roughly $38.3 million — by predicting private keys using only the device's serial number and internal clock. The vulnerability stems from a broken random number generator introduced in a 2021 firmware update, and a subsequent fix in 2022 failed to fully resolve the issue. Coinkite, the company behind Coldcard, is now urging all affected users to generate a new seed on updated hardware and move their funds immediately.
How the bug works
The flaw disables secure random number generation on certain Coldcard models. Attackers don't need physical access to the device. If they can see a wallet address or an exported public key, they can test guesses against the predictable private key — derived from the serial number and clock — and steal the funds. The exploit is similar to the Ill Bloom attack that drained wallets via weak seed phrases earlier this year.
Who is affected
Only the Coldcard Mk3 is vulnerable, and only if it's running firmware version 4.0.1 or later. The Mk4, Q, and Mk5 models are not affected. Coinkite and Block are still assessing the full extent of the flaw across older firmware versions. The vulnerability also extends to paper wallets and seed backups that relied on the same broken random number generator.
What users should do
Coinkite recommends generating a new seed on a device with the latest firmware and transferring all funds to the new wallet. A firmware update alone won't undo the damage — the old seed is already compromised. Users who added an extra passphrase to their seed face substantially lower risk, but Coinkite still advises moving funds as a precaution.
The company is still working to determine how many devices and wallets were affected by the bug, which went undetected for years. For now, anyone with a Coldcard Mk3 that was updated after 2021 should treat their seed as exposed. The clock is ticking — and the attackers are still guessing.
