Technical Root Cause
Published 7/31/2026, 7:36:45 AM
The Coldcard Mk3 hardware wallet security incident, which occurred on July 30, 2026, resulted in the theft of approximately 594.5 BTC (valued at roughly $38.3 million) from over 500 single-signature wallets. The attack was executed with extreme speed, with the majority of funds drained within a 15-minute window across Bitcoin blocks 960188 to 960191 [Source: https://atlas21.com/594-bitcoin-drained-15-minutes-theft/].
Technical Root Cause
The vulnerability is attributed to weak entropy in the seeds generated by the Coldcard Mk3's internal random number generator (RNG). Specifically, seeds generated on Mk3 devices between March 2021 and late 2023—using firmware versions 4.0.1 through 5.0.3—were found to be predictable if the user did not provide external entropy (such as dice rolls) or utilize a BIP-39 passphrase [Source: https://blog.coinkite.com/coldcard-mk3-seed-generation-warning/]. This predictability allowed attackers to pre-calculate private keys and drain funds once the vulnerability was weaponized.
Scope of the Flaw
- Affected Devices: The Coldcard Mk3 is the primary model confirmed to be at risk. While some researchers suggested potential risks for Mk2 and Mk4 models, Coinkite's official stance is that the Mk4, Mk5, and Q models remain unaffected due to different hardware architectures [Source: https://blog.coinkite.com/coldcard-mk3-seed-generation-warning/].
- Total Impact: While the primary coordinated drain involved 594.5 BTC, researchers identified an additional 488.1 BTC moved earlier with identical transaction fingerprints, potentially bringing the total impact to 1,082.6 BTC [Source: https://atlas21.com/594-bitcoin-drained-15-minutes-theft/].
- Mitigation Factors: Wallets using multi-signature setups, BIP-39 passphrases, or seeds generated via dice rolls (which bypasses the internal RNG) were not affected by this specific entropy flaw [Source: https://blog.coinkite.com/coldcard-mk3-seed-generation-warning/].
Comparison of Risk Factors
| Metric | Details | Source |
|---|---|---|
| Date of Incident | July 30, 2026 | [Source: https://atlas21.com/594-bitcoin-drained-15-minutes-theft/] |
| Primary Amount Stolen | 594.5 BTC (~$38.3M) | [Source: https://atlas21.com/594-bitcoin-drained-15-minutes-theft/] |
| Wallets Affected | ~500 single-sig addresses | [Source: https://blog.coinkite.com/coldcard-mk3-seed-generation-warning/] |
| Affected Firmware | 4.0.1 to 5.0.3 | [Source: https://blog.coinkite.com/coldcard-mk3-seed-generation-warning/] |
| Root Cause | Weak internal RNG entropy | [Source: https://blog.coinkite.com/coldcard-mk3-seed-generation-warning/] |
Official Response and Recommendations
Coinkite issued an urgent security advisory following the incident. Their primary recommendations for Mk3 users include:
- Immediate Action: Apply a strong, unique BIP-39 passphrase to the existing seed and move all funds to the new resulting addresses [Source: https://blog.coinkite.com/coldcard-mk3-seed-generation-warning/].
- Seed Replacement: Generate a new seed using the "Dice Roll" method (minimum 99 rolls) on firmware 4.1.9 or later, which hashes the rolls directly and bypasses the internal RNG [Source: https://blog.coinkite.com/coldcard-mk3-seed-generation-warning/].
- Hardware Migration: Migrate funds to a newer model (Mk4, Mk5, or Q) which utilizes different entropy generation mechanisms.
While the Coldcard CEO initially denied a device-wide vulnerability, the coordinated nature of the 594 BTC transfer led to widespread industry warnings for users of the Mk3 model [Source: https://atlas21.com/594-bitcoin-drained-15-minutes-theft/].