Coldcard Firmware Flaw Leads to $70 Million Bitcoin Theft

A critical firmware vulnerability in Coldcard hardware wallets has resulted in the theft of approximately $70 million in Bitcoin. The exploit allowed attackers to bypass the physical security of the devices by mathematically reconstructing private keys, rendering the "cold storage" defense obsolete.

In a rapid 41-minute window on July 30, 2026, attackers drained approximately 1,082.65 BTC from 1,196 different wallets. The theft was made possible by a firmware flaw that caused some devices to generate seeds using a weak software pseudo-random number generator (PRNG) instead of the intended hardware randomness generator (TRNG). This failure drastically reduced the entropy of the generated seeds, making the resulting private keys computationally enumerable. For users of Mk4, Q, and Mk5 models, the search space for these keys was reduced to roughly four billion possibilities—a range easily navigated by modern computing power.

The Failure of Cold Storage

Hardware wallets are designed to provide a "distance" defense, ensuring that private keys never touch an internet-connected environment. By keeping the keys offline, users are typically protected from remote hacking attempts. However, this specific exploit did not require the attacker to steal a key from a device; instead, it allowed them to rebuild the key from scratch. Because the randomness used to create the seed was predictable, the security of the wallet was compromised at the moment of creation, regardless of how securely the physical device was stored afterward.

Industry Implications

This incident undermines a core value proposition of the hardware wallet industry: the guarantee that a private key is truly random and therefore unguessable. The breach demonstrates that firmware-level flaws in randomness generation can render the most robust physical security useless. For the broader cryptocurrency market, this shifts the critical security challenge from the act of protecting a key to the verification that the key was generated correctly. It highlights a systemic risk where a single line of flawed code in a trusted manufacturer's firmware can expose thousands of users to total loss.

Current Status and Risks

Coldcard has identified that the vulnerability affects Mk2, Mk3, Mk4, Mk5, and Q models. The company has urged all affected users to immediately migrate their funds to new, secure wallets. While the primary attack window has passed, any wallet generated with the flawed firmware remains vulnerable to the same mathematical reconstruction. Users are advised to verify their firmware versions and avoid using any seeds generated on affected devices for future storage.