1,815 BTC Gone in 4 Waves: Coldcard's 40-Bit Entropy Flaw Is Still a Live Threat

Coldcard sweeps have already exposed about 1,815 BTC across four waves

This is still a live security event, not old news. Two large sweeps already pulled 1,082.65 BTC in 41 minutes and 594 BTC in 25 minutes from Coldcard wallets, and additional waves were flagged separately. The pattern suggests that vulnerable seeds are still being identified and monetized.

The core issue is the wallet's original seed generation flaw, which dates to March 2021. Any seed created on affected firmware during that window may still be exposed. A firmware patch can stop new weak seeds from being generated, but it does not fix seeds already created. That is why the real concern is not whether the bug existed; it is how many weaker keys may still be sitting in circulation.

The immediate risk is both liquidity and confidence. A third wave of sweeps was flagged before later activity emerged, showing that this was not a one-off incident. The easiest targets may already be gone, but as long as old seeds remain exposed and new sweeps continue to appear, investors should treat this as an active sentiment risk for affected Coldcard users.

The failure was a randomness collapse, not an exotic exploit

128-bit entropy fell to roughly 40 bits on Mk3

A standard 12-word BIP-39 seed is built around 128-bit seed target of entropy. On the Coldcard Mk3, the flaw reduced that to roughly 40-bit Mk3 entropy. That is a dramatic loss of security, not a minor edge case.

Other models were not fully safe either. Coinkite estimates roughly 72 bits of entropy on Mk4, Mk5, and Q devices instead of 128, so the issue extends beyond a single older board.

How an offline wallet became guessable

The failure started with firmware, not network access. A March 2021 firmware integration error routed seed generation to a deterministic software pseudorandom number generator instead of the STM32 hardware RNG. That software fallback was initialized from the chip's unique ID and timer registers and did not collect fresh entropy after initialization.

Block's analysis says an attacker who can constrain the device UID, timer state, and prior RNG-call history can reproduce candidate output streams offline. From there, the attack is straightforward: generate candidate seeds, derive addresses, and compare them with public blockchain data. In that sense, the wallet was no longer protecting users from key prediction.

Why Bitcoin's price did not flinch

Bitcoin's price barely reacted because this was a vendor-specific key-recovery problem, not a protocol failure. Still, the onchain cleanup showed how systematically funds were being collected: 562 BTC consolidated into one address. That suggests organized fund collection rather than a casual probe.

The distinction matters. Bitcoin's broader thesis is largely unchanged, but the trust case for any single device as a sole custodial layer has taken a hit. Hardware wallets are bought for per-key randomness, and when that breaks, the damage is both financial and symbolic.

What to watch as the attack pattern narrows

The near-term signal is still activity, not scale. Galaxy flagged a third wave of sweeps tied to weak Coldcard keys, while the earlier cleanup pattern ended with 562 BTC consolidated into one address. That matters more than the headline total now because it points to narrower, more methodical attacker behavior rather than a fully contained event.

What the market may be underpricing

This is a wallet-vendor flaw, not a Bitcoin protocol flaw, and the largest easy targets may already be gone. But custody distrust does not always show up immediately in spot volume. If affected holders start treating device security more cautiously, the sentiment effect can spread faster than the direct BTC losses suggest.

What to watch next

• Whether new sweeps continue beyond the earlier waves already documented
• Whether the consolidated address remains unmoved, which would suggest the attacker is still collecting methodically
• Whether new wallets created within the affected firmware window continue to show up as vulnerable

Positioning takeaway

For Bitcoin, the practical read is selective caution: stay constructive on the asset, but be less tolerant of custody single points of failure and sentiment shocks tied to device trust. That view weakens if new sweeps stop for a sustained period, the consolidated address remains untouched, and no fresh vulnerable wallets emerge.