The Incident at a Glance (July 30, 2026)
Published 8/3/2026, 10:37:03 PM
On July 30, 2026, hackers exploited a critical cryptographic entropy failure in Coldcard hardware wallets to steal approximately $70.2 million (1,082.65 BTC) in a single 41-minute window. The attack required no physical access to the devices because it targeted a flaw in how the wallets generated private keys, allowing attackers to "reconstruct" keys offline using high-powered computers.
The Incident at a Glance (July 30, 2026)
| Metric | Data Point |
|---|---|
| Total Stolen (Initial Wave) | ~1,082.65 BTC (approx. $70.2 Million) |
| Total Impacted (All Waves) | 1,367.05 BTC (~$89M) across 4,585 addresses |
| Primary Attack Window | 1:10–1:51 UTC (41 minutes) |
| Affected Devices | Coldcard MK2, MK3, MK4, and Q models |
| Root Cause | Firmware flaw (introduced March 2021) |
How the Hack Worked: The "Predictable" Seed
The security of a cold wallet depends on its ability to generate a truly random seed phrase. This attack succeeded because affected Coldcard devices were not using true randomness.
- The Firmware Flaw: In March 2021, a configuration error (
MICROPY_HW_ENABLE_RNG = 0) was introduced into the Coldcard firmware. This caused the devices to bypass their dedicated Hardware Random Number Generator (RNG). [Note: not independently confirmed] - Deterministic Fallback: Instead of hardware-grade randomness, the devices defaulted to a software-based pseudorandom number generator (PRNG). This software fallback was initialized using predictable data: the device's unique chip ID and internal timer values.
- Offline Brute-Forcing: Because the "ingredients" for the seed (chip ID and timer state) were limited or discoverable, attackers could simulate the seed generation process on their own hardware. They generated millions of candidate seeds offline without ever touching a victim's device.
- Blockchain Matching: Once the attackers generated a candidate private key, they checked the public Bitcoin blockchain to see if that key controlled any funds. When a match was found, they used the reconstructed key to sign a transaction and drain the wallet remotely.
Why Physical Access Wasn't Required
The attackers exploited the mathematical predictability of the keys. In cryptography, if the starting state (entropy) of a generator is known or guessable, the resulting "secret" key is no longer a secret. By the time the attack was launched, the hackers had likely spent months pre-calculating keys for thousands of potential chip ID and timer combinations.
Who Was Affected?
The vulnerability primarily impacted users who set up their wallets using the default "Generate" function on firmware released between March 2021 and July 2026. Users were generally safe if they:
- Used Dice Rolls: Manually entering 50+ dice rolls provided external entropy that bypassed the buggy firmware.
- Used a BIP-39 Passphrase: An additional "25th word" acted as a salt, making the final key unique even if the base seed was predictable.
- Pre-2021 Wallets: Wallets generated before the March 2021 update used the functional hardware RNG.
Current Status
As of August 3, 2026, the stolen 1,367 BTC remains largely unspent across seven primary attacker-controlled addresses. Coinkite (the manufacturer) released emergency firmware patches on July 31, 2026, to re-enable the hardware RNG. However, experts warn that updating the firmware does not secure an existing wallet; users who generated seeds on affected firmware must move their funds to an entirely new seed phrase to be safe.
Note: While research identifies the root cause as a firmware integration error, specific URLs for the technical post-mortems from 'TheHackerNews' or 'Block Engineering Blog' were not available in the research data.