Technical Mechanism: Entropy Collapse
Published 8/3/2026, 8:21:56 AM
The Coldcard exploit, which culminated in the theft of 1,367.05 BTC (approximately $88.6 million) between July 30 and August 1, 2026, was caused by a critical entropy collapse in the device's firmware. A coding error introduced in March 2021 bypassed the hardware random number generator (RNG), resulting in deterministic seed phrases that attackers were able to pre-calculate and sweep once funded [Source: https://blog.coinkite.com/coldcard-rng-vulnerability-advisory/].
Technical Mechanism: Entropy Collapse
The root cause was a firmware configuration error within the libngu library. The code incorrectly checked for the existence of the MICROPY_HW_ENABLE_RNG macro rather than its boolean value.
- RNG Bypass: Because the macro was present but set to zero, the device fell back to a deterministic software pseudorandom number generator (PRNG) called "Yasmarang."
- Predictable Initialization: This fallback PRNG was initialized using only the chip's unique ID and internal timer registers, providing no fresh environmental entropy.
- Entropy Reduction: For Mk3 devices, the intended 128-bit entropy collapsed to approximately 40 bits. For Mk4, Mk5, and Q models, entropy was reduced to roughly 72 bits [Source: https://blog.coinkite.com/coldcard-rng-vulnerability-advisory/].
- Exploitation: Attackers simulated these predictable initialization states offline to generate a massive database of potential seed phrases. They then monitored the blockchain for any addresses derived from these seeds and executed automated sweeps.
Timeline and Scope of the Drain
The theft occurred in three distinct waves, targeting different balance tiers and utilizing aggressive transaction fees to ensure priority confirmation.
| Attack Wave | Date (2026) | Addresses Drained | BTC Stolen | Estimated Value |
|---|---|---|---|---|
| Wave 1 | July 30 | 1,195 | 1,082.65 BTC | ~$70.2 Million |
| Wave 2 | July 31 | 1,478 | 76.16 BTC | ~$4.9 Million |
| Wave 3 | July 31 - Aug 1 | 1,912 | 208.24 BTC | ~$13.5 Million |
| Total | 4,585 | 1,367.05 BTC | ~$88.6 Million |
Data as of August 3, 2026 [Source: https://blog.coinkite.com/coldcard-rng-vulnerability-advisory/].
Affected Devices and Mitigation
The vulnerability affected Coldcard Mk2, Mk3, Mk4, Mk5, and Q devices running firmware released between March 17, 2021, and July 2026.
Users were NOT affected if they:
- Generated their seed using 50+ physical dice rolls (which bypasses the internal RNG).
- Created their seed prior to March 17, 2021.
- Used a strong BIP-39 passphrase, which adds independent entropy that the attackers could not pre-calculate.
Current Status: Coinkite has released emergency firmware updates (Mk3 v4.2.0, Mk4/5 v5.6.0, Q v1.5.0Q) to restore the correct hardware RNG path. However, updating the firmware does not secure an existing compromised seed; affected users must generate a new seed on the patched firmware and migrate their funds immediately [Source: https://blog.coinkite.com/coldcard-rng-vulnerability-advisory/].