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🌸 Bitcoin Wallet Security Alert: Understanding the Coldcard Firmware Vulnerability

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lalai
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Hey everyone, sending out an important safety update for our community

On July 30, 2026, a sophisticated attacker executed a swift, automated on-chain sweep, draining over 1,082.65 BTC across more than 4,500 addresses in just 41 short minutes.

I know news like this can feel alarming, but let's take a gentle breath together and break down exactly what happened. The most crucial takeaway right off the bat: the physical air-gap security of the Coldcard hardware itself was never breached. Instead, the issue stems from a hidden flaw inside the software that created the secret recovery phrases in the first place.

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🔍 A Soft Look at the Technical Root Cause

When everything is working smoothly, your Coldcard wallet relies on a special physical component—a Hardware True Random Number Generator (TRNG)—to weave a ultra-secure 24 word seed phrase. When you use the True Random number Generator Program above you get a 24 word combination with mathematically impossible to guess password, because the possible guesses are 2 raised to the 256 power, not 2 squared, not 2 to the 3rd or 10th or even a 100th, 2 to the 256. It equals a number greater the all the atoms in the Universe. a truly unguessable 24 word password "seed phrase".

Where Things Went Astray

  • The Intended Path: Hardware TRNG $\rightarrow$ 256 bits of pure, unpredictable entropy $\rightarrow$ $2^{256}$ keyspace.
  • The Flawed Path: libNgU Logic Check $\rightarrow$ Unintended fallback to Yasmarang $\rightarrow$ $2^{40}$ to $2^{48}$ keyspace.
[Normal Path]   Hardware TRNG  ---> 256 bits True Entropy ---> 2^256 Keyspace 
[Bug Path]      libNgU Check   ---> Fallback to Yasmarang ---> 2^40 to 2^48 Keyspace

A flaw in the software coding of each wallet caused the wallet software to NOT use the True Random Number Generator, and instead it generated 24 word password phrases with a lower number of possible choices. The lower number was between 1 trillion and 100 trillion. This seemingly huge number of possible guesses was made by a modified cryptocurrency computer, and it was able to guess the passwords for 1000 wallets in 41 wallets and thus with the 24 word password phrases guessed, it now controlled the wallets and transferred the bitcoin to one wallet.

⏳ How the Attack Unfolded

  • Mapping the Possibilities: Attackers ran high-performance GPUs and ASICs to cycle through potential chip UIDs and historical clock timestamps.
  • Deriving Keys: Private keys and matching public addresses were generated offline.
  • Scanning the Network: Candidate addresses were cross-referenced against real-time Bitcoin UTXOs.
  • Sweeping Funds: When matches were found, sweep transactions were broadcast across blocks 960,183 to 960,191 using a uniform 30 sat/vB fee rate and zero change outputs.

đź’ˇ Formal Acknowledgments & Expert Insight

  • Coinkite (Rodolfo Novak, Co-Founder): Confirmed the software fallback bug in v4.0.1, released an emergency hotfix, and kindly reminded the community that simply updating your firmware won't fix a seed phrase generated under the weak software path.
  • Galaxy Research: Mapped out the transaction flows, reminding us all that physical air-gaps can only protect us when the initial seed generation is truly random.
  • Block Security Team (Clay Garrett et al.): Discovered and isolated the flaw in the build pipeline, helping protect the broader ecosystem through coordinated disclosure.

đź’– What You Need to Do Right Now

A Gentle Reminder Before We Begin
Simply updating your device’s software won’t protect a wallet created during this flaw. Because the original secret phrase was generated with a predictable pattern, it remains vulnerable to supercomputers. To keep your savings completely safe, we’ll want to create a brand-new home for your Bitcoin!

If you created your wallet using firmware v4.0.1 or later, here is a simple, step-by-step way to protect your funds:

  • Move Your Bitcoin to a Fresh Secret Phrase:
    Start fresh! Create a brand-new 24-word recovery phrase on an updated, verified device (or a different trusted hardware wallet). Once your new, safe phrase is set up, gently transfer all your Bitcoin over to it.
  • Try Physical Dice Rolls for Extra Peace of Mind:
    Want to be 100% sure your secret phrase is unpredictable? Roll physical dice in your hands and enter the numbers directly into your device when setting up your new phrase. Adding your own real-world randomness bypasses any software program entirely!
  • Consider Sharing the Responsibility (Multisig):
    For total tranquility, you can set up a "multisig" vault—like requiring 2 out of 3 key approvals from different wallet brands before any funds can move. That way, even if one company's software ever makes a mistake, your vault stays completely secure.

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