COLDCARD: an RNG flaw in the firmware allowed the theft of $88.6 million in Bitcoin

A vulnerability in the random number generator of the COLDCARD firmware allowed attackers to reconstruct the private seeds of thousands of wallets and drain their funds.

What happened

BleepingComputer reports that a vulnerability in the random number generator (RNG) of the COLDCARD (Coinkite) hardware wallet firmware likely allowed the theft of $88.6 million in Bitcoin from thousands of wallets whose seeds were generated with this faulty firmware.

The fundamental issue: the security of a hardware wallet relies entirely on the entropy of the initial seed. If the RNG generating this seed is predictable or biased, an attacker with sufficient computing power can brute-force the seeds and reconstruct the private keys—without ever touching the hardware itself.

What we know

• Affected firmware: Earlier versions of COLDCARD firmware with a bias in their RNG
• Attack vector: No physical access, no phishing—pure exploitation of the RNG bias to remotely recalculate seeds
• Estimated amount: $88.6 million in Bitcoin (BleepingComputer, 2026-08-02)
• Victims: Thousands of wallets whose seeds were generated during the vulnerability period

Analysis

The RNG is the Achilles' heel of any cryptographic system. This is why standards like NIST SP 800-90A exist, and serious hardware wallets have their entropy generators audited independently. A bug in this layer is catastrophic because it is undetectable without an audit of the source firmware—the user has no way of knowing their seed is weak.

This type of attack is particularly insidious: funds can be stolen months or years after the wallet is generated, when the attacker decides to act.