Aug 21, 2026 · 1h 23m
Coldcard flaw exposed thousands of bitcoins to predictable-wallet attacks
The Coldcard Disaster: Everything You Need to Know | Lloyd Fournier & Nick Farrow
The incident shows how a defective randomness source can defeat otherwise careful self-custody practices and force users to rethink wallet design, backups, and trust.
- 1A weak random-number generator made seeds from certain Coldcard devices searchable, affecting roughly 1,200 wallets and nearly 2,000 Bitcoin.
- 2AI-assisted analysis helped reproduce the attack, while on-chain evidence indicated multiple attackers and exposed gaps in review and disclosure.
- 3FrostSnap and multivendor multisig reduce dependence on one device, but simpler backups and geographically distributed custody remain essential.
Don't miss
Nick Farrow describes reproducing the vulnerable-seed attack with AI assistance and tracing affected wallets on-chain.
The brief
Lloyd Fournier and Nick Farrow examine a Coldcard vulnerability that made some generated seeds predictable, putting roughly 1,200 wallets and nearly 2,000 Bitcoin at risk.
The technical failure centered on a flawed Yasmarang random-number generator in MicroPython, shrinking seed entropy to a searchable range despite the device’s other safeguards.
AI-assisted reproduction and on-chain tracing helped distinguish real compromises from false alarms, while evidence suggested multiple attackers and raised questions about audits and disclosure.
The episode challenges familiar fixes: dice rolls, passphrases, air gaps, and open source can all fail when the device or implementation cannot be trusted.
FrostSnap offers a different model by combining randomness across devices and using threshold signatures, but the broader lesson is simpler custody, stronger backups, and distributed physical storage.
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