An ongoing exploit targeting Coldcard, one of Bitcoin’s most trusted hardware wallets, has drained nearly $89 million in Bitcoin from thousands of victims — and researchers warn the attack may still be active.
What makes the theft especially alarming is that it defeats the entire premise of cold storage: victims’ private keys were never connected to the internet, never touched by malware, and in some cases sat inside bank safety deposit boxes for years. The attacker never needed physical access to a single device.
How the Losses Escalated
The attack began Friday, July 30, 2026, when a first wave swept 594 BTC — roughly $38 million — from approximately 500 wallets in a single 25-minute window between 01:31 and 01:56 UTC.
Galaxy Research, the blockchain analytics firm tracking the incident, subsequently reported the total climbing rapidly: by July 31, the figure had roughly doubled to 1,082.65 BTC (about $70 million) stolen from 1,196 addresses within a 41-minute burst, traced to four attacker-controlled wallets.
A second wave identified August 1 pushed losses to 1,158.66 BTC (~$75.1 million) across 2,673 addresses. By August 2, a third wave brought the running total to 1,367 BTC — nearly $89 million — drained from 4,585 addresses. Alex Thorn of Galaxy Research has since flagged signs of what may be a fourth organized wave occurring in real time, suggesting the exploit remains unresolved.
Victims Speak Out
The human toll became visible quickly on social media. Fitness entrepreneur Jonathan Goodman wrote that his Bitcoin had been held in a Coldcard device inside a safety deposit box that had “never been connected to the internet.”
Between 9:36 PM and 9:43 PM on July 29, he said, every wallet he owned was emptied — 18.25 BTC, worth just over $1.6 million CAD, gone in seven minutes. Other users have reported losses exceeding $1 million each, with the attacker reportedly targeting the largest balances first before moving to smaller wallets in later waves.
The Technical Root Cause: A Five-Year-Old Randomness Bug
According to Coinkite, the Canadian manufacturer behind Coldcard, and independent security researchers at Block’s Bitcoin engineering team, the vulnerability traces back to a firmware build released in March 2021.
A configuration error caused certain Coldcard devices to bypass their dedicated hardware random number generator — the component responsible for producing truly unpredictable entropy — and instead fall back to a software-based pseudo-random number generator seeded using non-secret data, including the device’s internal clock and serial number.
A properly generated Bitcoin seed phrase should draw on 128 bits of entropy, a number so astronomically large that brute-forcing it is computationally impossible even with the world’s most powerful supercomputers. But because the flawed devices generated seeds using predictable, semi-public inputs rather than genuine randomness, attackers could mathematically reconstruct the likely universe of possible seed phrases entirely offline — without ever touching, hacking, or physically accessing the victim’s device. Once a matching seed was calculated, the attacker held the private keys and could drain the wallet within minutes.
Notably, a review by Block’s security team found the flaw extended beyond standard wallet seeds: the same faulty generator also produced Coldcard’s paper wallet private keys, seed-splitting backup masks, device-cloning keys, and Key Teleport transfer codes — meaning the exposure was broader than initially understood.
Which Devices Are Affected
Coinkite has identified Coldcard Mk3 devices running firmware versions 4.0.1 through 4.1.9 as carrying the highest confirmed risk, with the underlying flawed code introduced in firmware 4.0.0. The company and independent researchers say newer models — the Mk4, Mk5, and Coldcard Q — appear unaffected based on current investigation, though Coinkite has cautioned that its review is ongoing and has not ruled out broader exposure.
Critically, Coinkite has stressed that simply updating a device’s firmware does not fix an already-compromised seed. Because the weakness lives in the seed phrase itself — not in the physical hardware — any wallet whose seed was originally generated under vulnerable firmware remains at risk indefinitely unless the user generates a completely new seed and migrates all funds to a fresh wallet.
Why Analysts Say Cold Storage Isn’t the Problem — Implementation Is
Security analysts have been quick to draw a distinction between the concept of cold storage and this specific implementation failure. The core promise of hardware wallets like Coldcard is that private keys are generated and stored in an “air-gapped” environment, fully isolated from any internet-connected device, using QR codes or microSD cards to transfer signed transactions. That architecture remains sound in principle — the failure here was not that the wallet was connected to anything, but that the randomness underpinning the seed generation itself was compromised at the software level.
Analysts covering the incident have emphasized that self-custody security ultimately rests on trusting that a device’s internal code correctly implements true randomness — something ordinary users have no practical way to independently verify. Devices that incorporated additional entropy sources, such as manual dice-roll seeding or a BIP-39 passphrase layered on top of the standard seed, were reportedly not vulnerable, since those extra steps introduce randomness the flawed generator could not predict.
Market and On-Chain Ripple Effects
The incident has also distorted broader Bitcoin market signals. CryptoQuant analyst JA Maartunn noted that roughly 77,402 BTC from older, long-dormant wallets moved on-chain following public disclosure of the vulnerability, temporarily skewing metrics like Coin Days Destroyed and Long-Term Holder Supply Change that analysts typically use to gauge investor sentiment.
Maartunn cautioned against reading these movements as a sign of mass selling, attributing the activity primarily to concerned holders proactively securing funds rather than capitulating. Unlike prior crypto collapses such as FTX, the Coldcard incident has driven some investors to move Bitcoin toward exchanges as a temporary safety measure rather than triggering broad market panic — Bitcoin’s price has shown limited direct reaction to the theft.
What Coinkite Is Telling Users
Coinkite CEO Rodolfo Novak has urged all Coldcard owners to act immediately: “If you generated a seed using a Coldcard wallet, move your funds now, using our updated best practices, before reading further.” He also asked the broader community to help spread the warning to Coldcard owners who may not be actively following crypto news, noting that “every hour matters.”
At the same time, Coinkite has cautioned against panic-driven mistakes, stating that “rushing a wallet migration can create a more immediate risk than the issue you are trying to address” — an acknowledgment that hastily transferring funds without proper precautions could itself expose users to error or additional theft.
What Affected Users Should Do
Security researchers and Coinkite recommend that any Coldcard owner immediately determine which device model and firmware version generated their existing seed. Anyone who created a wallet on an Mk3 device without using dice-roll entropy or a passphrase should treat their funds as compromised, generate an entirely new seed on updated, patched firmware, and migrate all Bitcoin to the new wallet as quickly as safely possible — while avoiding rushed, error-prone transfers that could compound the damage.