Block Engineering

COLDCARD Wallets Suffer Mass Crypto Theft After RNG Flaw Allows Seed Reconstruction

A critical implementation error in COLDCARD hardware wallets enabled attackers to reconstruct wallet seeds and steal cryptocurrency from thousands of users. The flaw stemmed from an incorrect switch to the libsecp256k1 library, which inadvertently used the rng_get() function from libNgU for seed generation instead of proper hardware entropy. Depending on the model, seeds for Mk2 and Mk3 devices could be derived solely from UID, timer state, and generator history, while Mk4, Mk5, and Q models added limited extra entropy. On July 30, the attacker drained over 1,367 BTC worth approximately $88 million from 4,585 addresses in just 41 minutes. Coinkite released updated firmware, but affected users must also regenerate new seeds and consider additional protections such as passphrases. Other Coinkite products including TAPSIGNER, OPENDIME, and SATSCARD remain unaffected. The incident highlights how even well-tested cryptographic libraries can fail when integrated incorrectly.