Coldcard Firmware Flaw Leads to Over $130 Million in Bitcoin Theft

A critical cryptographic vulnerability in Coldcard hardware wallet firmware has resulted in the theft of more than $111 million in Bitcoin, with total losses estimated to exceed $130 million. The flaw allowed attackers to bypass the devices' physical security by brute-forcing private keys derived from weak seed phrases.

The vulnerability originated from a 2021 code error that affected MK3 devices and specific firmware versions of the MK4. The flaw occurred when the device's random number generator (RNG) encountered insufficient entropy, causing it to fall back to a predictable algorithmic pattern. This deterministic output meant that seed phrases—the master keys to a user's funds—were not truly random, enabling threat actors to calculate them offline. Data from Galaxy Research indicates that the theft was not a single coordinated campaign but was instead carried out by at least 12 separate, unaffiliated threat actors who exploited the flaw after technical details became public.

The Failure of Air-Gapping

Coldcard wallets are marketed as high-security, air-gapped devices designed to ensure private keys never touch an internet-connected environment. However, because the vulnerability existed at the point of seed generation, the physical isolation of the device provided no protection. Attackers did not need to compromise the hardware or steal the physical device; they simply needed to replicate the flawed algorithmic pattern to derive the keys.

One victim, Jonathan Goodman, reported losing approximately $1.6 million despite following strict security protocols. Goodman stated that he had kept his device air-gapped in a safety deposit box, noting, "I did everything right, yet all because the hardware that created the seed phrase originally had one line in their code from 2021 that had a vulnerability."

Industry Implications

This incident represents a fundamental failure of cryptographic security in a product trusted for absolute custody. It serves as a stark reminder that physical air-gapping is irrelevant if the underlying entropy generation is flawed. For the broader hardware wallet industry, the breach highlights a critical need for the formal verification of RNG processes to ensure that the mathematical foundations of seed generation are immutable and truly random.

What's Next

As the full scale of the losses becomes clearer, the industry is watching how other hardware providers audit their entropy sources. While the specific Coldcard flaw has been identified, the event has shaken user confidence in the assumption that "cold storage" is an absolute guarantee of safety. Users are now being urged to verify their firmware versions and, in cases of suspected compromise, migrate funds to new wallets generated with verified entropy.