Coldcard Wallets Exposed: Over 1,082 BTC at Risk Due to Critical Security Flaws

A potential security threat has been discovered in multiple generations of Coldcard hardware wallets. Block's engineering and security teams reported an investigation into remote Bitcoin theft from non-Bitkey wallets, which revealed critical vulnerabilities in devices such as Coldcard Mk2, Mk3, Mk4, Q, and Mk5.

The first vulnerability affects the Coldcard Mk2 and Mk3 firmware due to a coding error that caused wallet generation to rely on predictable values instead of sufficient hardware-generated randomness.

For newer Mk4, Q, and Mk5 devices, a flaw reduced additional randomness to just 32 bits during boot using secure-element input. Importing an affected seed into another wallet does not eliminate the threat, as the compromised seed remains vulnerable if a wallet was created on vulnerable Coldcard firmware.

Block's preliminary analysis suggests that over 1,082.59 BTC could be at risk due to these security flaws. Security engineer Clay Garrett noted that researchers identified 695 earlier transactions with matching on-chain fingerprints, accounting for an additional 488.11 BTC.