Coldcard Wallet Exploit Enables $70 Million Bitcoin Heist

On July 30, an attacker drained 1,196 Bitcoin addresses in 41 minutes, taking 1,082.65 BTC worth about $70.2 million at the time ¹. Galaxy Research traced the sweep to a firmware flaw first introduced in March 2021 when Coldcard’s developers integrated a deterministic PRNG into its seed‑generation routine. Instead of using true randomness, the firmware routed key creation through this predictable algorithm, allowing an attacker who could model the PRNG state to generate valid private keys for many wallets simultaneously.

Coldcard is manufactured by Canadian firm Coinkite and markets the device as a “Bitcoin‑only” hardware wallet that claims to keep all cryptographic operations offline. The new evidence shows that even such isolated devices can be compromised if their internal randomness is not truly unpredictable. In practice, the attacker likely precomputed a set of keys and then matched them against live Coldcard addresses discovered via blockchain analysis tools. Once a match was found, the corresponding account was drained before the owner could react.

The speed of extraction suggests sophisticated tooling rather than opportunistic theft. Similar incidents have occurred with other crypto custodians: the BitPoint exchange hack of 2018 saw attackers exploit a flawed random number generator to siphon ¥35 million (~$369k USD). These events underscore how deterministic PRNGs remain a critical weakness in otherwise secure hardware wallets. For comparison, Trezor uses both a TRNG for seed generation and separate post‑compromise signing keys—an approach recommended since early 2018 when Satoshi Nakamoto’s original design specification highlighted these tradeoffs.

Beyond the immediate financial loss, this breach raises broader privacy concerns. Wallet owners rely on the promise that a cold storage device will never expose private keys to network traffic or malicious code. If an attacker can predict key material from firmware, they effectively bypass that guarantee.

Security advisories urge all Coldcard users to update their firmware immediately if newer releases are available, as later versions reportedly replace the faulty PRNG routine with a true entropy source.

The Coldcard exploit demonstrates how a seemingly minor design choice—routing seed generation through a deterministic PRNG—can translate into a catastrophic privacy breach when it comes to light. The $70 million loss serves as both a warning and a call to action: vendors must audit randomness sources, and users must stay vigilant about firmware updates and device provenance.