Coldcard RNG flaw enables $89M Bitcoin wallet theft
CriticalAffected firmware ranges
- Mk2 / Mk3: versions 4.0.1 (March 2021) through 4.1.9 inclusive
- Mk4, Q, Mk5: all releases before the fixed firmware updates (approx. 72 bits entropy instead of 128)
- Safe if seed created with ≥50 independent dice rolls + strong unique BIP-39 passphrase
What happened
Attackers drained an estimated $89 million in Bitcoin from Coldcard hardware wallets in multiple waves starting July 30, 2026, by exploiting a legacy firmware flaw that produced weak wallet seeds.
The bug, present since March 2021, caused some wallets to fall back to a deterministic software RNG instead of the hardware RNG when generating seeds. This allowed offline reproduction of private keys for addresses whose seeds lacked sufficient entropy (e.g., fewer than 50 dice rolls) or a strong BIP-39 passphrase. Galaxy Research tracked the initial automated sweep of 1,082.65 BTC ($70m) from 1,196 addresses in 41 minutes, with totals later reaching ~1,367 BTC across 4,385 addresses. Coinkite has released fixed firmware.
Who is affected
Owners of Coinkite Coldcard Bitcoin-only hardware wallets (Mk2, Mk3, Mk4, Q, Mk5 models) whose seeds were generated on affected firmware without adequate additional entropy or a strong unique passphrase.
Specifically at risk: Mk2/Mk3 versions 4.0.1 through 4.1.9, and Mk4/Q/Mk5 before the latest fixed releases (which provided only ~72 bits of entropy instead of 128). Thousands of addresses were hit; the attack remains ongoing for unmoved funds.
Why it matters
Hardware wallets are trusted as the gold standard for cold storage of high-value crypto. A multi-year entropy failure turning seeds into guessable keys undermines that trust and enables silent, automated mass theft without physical access or malware on the device itself.
Operators and holders of significant BTC balances face immediate total loss risk; the speed and scale show how quickly weak crypto primitives can be monetized once discovered.
How it could have been prevented
Immediately move any funds from potentially affected Coldcard single-sig wallets to a newly generated seed on updated firmware or another secure wallet. Install the latest Coinkite firmware on all devices before generating any new seeds.
When creating seeds, always use at least 50 fair dice rolls plus a strong unique BIP-39 passphrase. Treat any seed created on the listed vulnerable versions without those steps as compromised and retire it.
Relevant professional terms
- Hardware wallet
- A physical device that stores cryptocurrency private keys offline and signs transactions without exposing the keys to an internet-connected computer.
- Deterministic RNG fallback
- A secondary random-number generator that produces predictable outputs from a fixed seed or algorithm when the primary hardware entropy source fails or is unavailable, destroying cryptographic security.
