Coldcard Security Flaw Raises Concerns Over Bitcoin Wallet Safety

A critical seed generation issue has been identified in specific Coldcard hardware wallets. The vulnerability stems from a flaw in firmware versions for the Mk3, Mk4, Mk5, and Q devices. This defect replaced secure random number generation with a predictable software process, which significantly lowered the entropy of generated seed phrases. When entropy is low, a seed becomes much easier for an attacker to guess, putting the funds at risk.

The impact of this flaw is significant. Reports indicate that approximately 594 BTC were taken from around 500 single signature wallets between July 30 and July 31, 2026. Because a single signature wallet relies entirely on one seed, there was no secondary layer of protection to stop unauthorized transactions once the seeds were compromised.

Not every user is affected, however. Devices using newer, patched firmware are secure, as are wallets created using BIP 39 passphrases or manual dice rolls for entropy. These additional steps effectively override the weak random number generator. If you use a Coldcard, you should check your specific firmware version and how your seed was initially created.

This event serves as a stark reminder that self custody requires constant vigilance. While hardware wallets are generally reliable, they are not immune to technical errors. Moving forward, users should stay updated on official security advisories and consider using multisig configurations or additional entropy methods to build a more resilient storage strategy.