Coldcard Exploit Traced to Faulty Random Number Generation

Galaxy Research has tracked approximately 1,596 Bitcoin stolen across three confirmed waves of attacks on Coldcard devices, with suspected additional losses bringing the total to around 2,055 BTC—roughly $130 million at current prices. At least 15 separate attackers have exploited the vulnerability, with one sweep moving $70 million in 41 minutes.

Coinkite's technical analysis reveals the root cause: a 2021 migration to the libsecp256k1 cryptography library inadvertently rerouted seed generation away from Coldcard's hardware random number generator to MicroPython's Yasmarang software fallback—designed for devices without a randomness chip. A build guard using the #ifndef directive failed to properly check whether the randomness setting was enabled, causing the hardware random number generator to be bypassed even though the device possessed one.

On Mk2 and Mk3 devices running firmware versions 4.0.1 through 4.1.9, the entropy derived only from the chip's serial number and clock, creating a search space of approximately 40 bits. This dramatically reduced entropy allowed attackers to recover private keys through brute-force calculation, despite the wallets never connecting to the internet. Coinkite acknowledged in its technical statement that the bulk of randomness was unexpectedly coming from a pseudo-random number generator in the codebase that the company had not realised was being used.