Overview
- Researchers say a March 17, 2021 firmware change caused Coldcard devices to fall back from the hardware RNG to a predictable MicroPython/Yasmarang software PRNG when creating seeds.
- Coinkite disclosed the vulnerability on July 30, 2026 and released emergency patched firmware on July 31, 2026, but the company warns that installing the patch does not fix seeds already generated with the flaw.
- On-chain forensics have tracked multiple coordinated sweep waves that have drained roughly 1,596–1,719 BTC (about $100–$111M) with broader estimates under active vetting up toward ~2,055 BTC (about $130M).
- Technical analysis shows the fallback used device identifiers and timers instead of fresh entropy, reducing effective seed strength to as low as ~40 bits on some models and making brute-force reconstruction practical for attackers.
- Coldcard is preparing a technical post‑mortem and advising affected users to generate new seeds on patched devices, add independent physical entropy or a strong BIP‑39 passphrase, and migrate funds to secure wallets before resuming use.