A flaw in Coldcard's random number generation has left hundreds of Bitcoin wallets vulnerable, with a single theft now pegged at $38 million and climbing. The issue, tied to weak entropy in the wallet's seed creation process, allowed attackers to predict or reconstruct private keys for affected users. Loss estimates continue to rise as more compromised wallets are identified.
How the flaw works
The vulnerability stems from Coldcard's random number generator, which failed to produce sufficiently unpredictable seeds during a specific period. This meant that wallet seeds—the master keys to a user's funds—were not truly random. Attackers who understood the flawed algorithm could generate the same seeds and drain the corresponding wallets.
The problem is not a remote exploit or a firmware bug that allowed unauthorized access. It is a cryptographic weakness at the very foundation of wallet creation. Once the pattern was discovered, the theft became a matter of computation rather than luck.
Who was affected
Coldcard has not released an official count, but sources indicate that hundreds of wallets were created with the weak seeds. The $38 million theft is the largest known incident linked to the flaw, but the number is expected to grow as forensic analysis continues. The affected wallets were likely created during a specific timeframe, though the exact window has not been publicly confirmed.
Users who generated their Coldcard wallet during the vulnerable period are at risk, even if they have not yet lost funds. The attacker appears to have systematically swept wallets with predictable seeds, but some may remain untouched.
Coldcard's response
The company has acknowledged the issue and released a firmware update that addresses the randomness problem. However, the fix only prevents future wallets from being created with weak seeds. It does not retroactively secure wallets that were already generated. Coldcard has advised users to migrate funds from any wallet created during the affected period to a new wallet with properly generated seeds.
The timing of the disclosure is notable. Coldcard has long marketed itself as a security-focused hardware wallet, favored by privacy-conscious Bitcoiners. A flaw in its core randomness process undermines that reputation.
What users should do now
Anyone who set up a Coldcard wallet in the last year should check whether their device was affected. The company has provided a tool to test whether a seed was generated with sufficient entropy. If the test fails, the wallet should be considered compromised. Users should create a new wallet on an updated device and transfer funds immediately.
The broader question is how the flaw went undetected for so long. Coldcard's code is open source, and the random number generator had been audited. But the vulnerability slipped through. That raises uncomfortable questions about the limits of even audited open-source hardware.
The $38 million figure is not final. As more wallets are scanned and the attacker's activity traced, the total could climb. For now, the incident stands as one of the costliest hardware wallet failures in Bitcoin's history.
