A security failure affecting COLDCARD hardware wallets has delivered a costly reminder that cryptocurrency protection ultimately depends on the quality of the numbers used to create private keys. Researchers believe a firmware error made wallet seeds predictable enough for an attacker to reconstruct them and steal approximately $88.6 million in Bitcoin.
Hardware Security Undermined by Software
COLDCARD devices include a hardware random number generator intended to provide cryptographically secure entropy. However, an integration error reportedly caused affected firmware to use MicroPython's deterministic Yasmarang fallback generator instead. That fallback relied on values such as a device identifier and system timing, which were not sufficiently unpredictable for generating wallet recovery seeds.
An attacker able to estimate or reconstruct those values could generate candidate seeds offline. The corresponding Bitcoin addresses could then be calculated and compared with the public blockchain. Once a match was found, the attacker could derive the private keys and transfer the funds without stealing the physical wallet.
Blockchain researchers identified several waves of suspicious transactions. The estimated total reached 1,367 Bitcoin taken from 4,585 addresses. The consistent transaction fees and absence of change outputs indicate that an automated system may have swept previously identified wallets.
Updating Firmware Is Not Enough
Coinkite has released corrected firmware for affected COLDCARD models, but installing the update does not make an existing seed secure. Anyone whose seed was generated by vulnerable firmware must treat that seed as potentially exposed.
Recommended Response
- Confirm that the existing wallet backup is available and readable.
- Install the appropriate fixed firmware release.
- Generate and securely record an entirely new seed.
- Verify the receiving address directly on the hardware device.
- Send a small test transaction before transferring the remaining balance.
- Retain the old backup until the migration has been successfully confirmed.
In my view, this incident challenges the assumption that a hardware wallet is automatically safer than a software wallet. A secure chip cannot compensate for flawed entropy handling elsewhere in the firmware. Wallet manufacturers should subject seed-generation paths to independent testing, reproducible builds and continuous statistical validation. Users, meanwhile, should remember that firmware updates can prevent future exposure, but they cannot repair cryptographic secrets that were weak from the moment they were created.
([bleepingcomputer.com](https://www.bleepingcomputer.com/news/security/coldcard-wallet-rng-flaw-likely-linked-to-88-million-bitcoin-theft/))