Coinkite released Coldcard firmware 5.6.1 requiring manual user entropy after a $100M exploit exposed seeds generated between 2021–July 2026; users must migrate funds to new seeds.
Security & Exploits ·
Coinkite has released firmware 5.6.1 for Coldcard devices following a random-number generator vulnerability that exposed customer funds. The update mandates manual entropy input—via dice rolls, coin flips, or timed keystrokes—before any new wallet seed can be generated, and replaces the compromised software path with a SHA-256 Hash_DRBG verified at device boot.
The defect originated from a build error in March 2021 that left a software random-number path enabled despite hardware-only design intent, routing seed entropy through MicroPython's Yasmarang PRNG instead of the device's dedicated hardware generator. This reduced entropy to roughly 72 bits instead of 128, allowing attackers to derive private keys; confirmed losses exceeded $100 million, with the largest wave sweeping 594.5 BTC from 500 addresses on July 30. The firmware also adds transaction signature verification to prevent compromise via malicious USB hosts.
Critically, installing 5.6.1 does not remediate seeds already generated on vulnerable firmware between 2021 and July 2026. Affected users must create new seeds and transfer their Bitcoin; the company notes the update and accompanying security review do not constitute a complete audit of the firmware binary. Mk2 and Mk3 models remain outside this release cycle.