Coldcard

Is Coldcard safe?

The design is among the strictest you can buy, but in 2026 it failed at the most basic task. A Coldcard keeps Bitcoin keys on a device with two secure elements, can sign without ever touching a computer, and publishes its firmware source. Yet from March 2021 a firmware bug made it generate seeds with far too little randomness, and in July and August 2026 attackers used that to take more than 1,300 BTC. We score Coldcard 65/100, a C.

If you own a Coldcard, the first question is whether your seed was created on affected firmware. If it was, updating is not enough: you need a new seed and to move your coins.

What went wrong in 2026

On 30 July 2026 Block's Bitcoin engineering and security teams published a report after Coldcard users began losing funds. A build setting disabled the hardware random-number generator in the MicroPython layer, and a guard in Coinkite's library checked only whether that setting existed, not whether it was switched on. Seed generation therefore fell back to a software generator seeded from the chip's ID and timers. On the Mk4, Q and Mk5, secure-element entropy was mixed in, but only 32 bits of it.

Coinkite's advisory gives the scope. Seeds from Mk2 and Mk3 firmware 4.0.1 (March 2021) to 4.1.9 are at risk unless at least 50 private dice rolls were added or the wallet has a strong, unique passphrase. Seeds made on the Mk4 and Mk5 before 5.6.0, and on the Q before 1.5.0Q, have about 72 bits of entropy instead of 128. Fixed firmware for every model followed within days.

The thefts were fast. Galaxy Research tracked a first wave on 30 July that took 1,082.65 BTC from 1,196 addresses in 41 minutes, and counted 1,367 BTC (about $88.6 million) from 4,385 addresses by 2 August. Crypto Briefing later reported verified thefts of 1,596 BTC from about 7,300 addresses. Coinkite declined to confirm those figures and has not announced compensation; it says a formal post-mortem will follow. Large, unrepaid losses caused by the wallet's own code put the security record at 30, above Atomic Wallet (20), whose 2023 cause was never explained, and below Electrum (48).

The incident has also changed how long Coinkite keeps buyers' details. Normally it blanks customer records 120 days after delivery, keeping only an email address and country. On 7 August 2026 it said it had paused that blanking "until further notice" because of legal duties tied to "ongoing and anticipated legal proceedings", with access limited to authorised staff. Coinkite says it will resume normal blanking as soon as it is legally permitted; questions go through its support form.

How Coldcard protects keys now

The protections around the key are strong. Two secure elements from different vendors guard the PIN and seed, a light at boot shows whether the firmware matches what the secure element recorded, and the device can work fully offline, passing transactions on a microSD card, by QR code on the Q or over NFC. It supports BIP-39 passphrases, multisigMultisigA crypto wallet that needs approval from several keys to move funds, for example any 2 of 3, rather than from a single key.More in the glossary, dice-roll seeds and decoy PINs.

Since the fix, new seeds combine the hardware generator with at least 65 random key presses, 50 dice rolls or 128 coin flips. Independent reviewers checked the remediation, and one confirmed on a real Mk4 that the hardware generator is now used. Key security still scores 80, not 90, because the seed generator failed on every model for five years and existing seeds stay weak until each owner migrates.

Open source, with a catch

Coldcard's firmware has been on GitHub since 2018 under the MIT licence with a Commons Clause, which forbids selling products built on the code. That makes it source-available rather than open source. An outside developer has rebuilt firmware 5.6.0 and matched every byte of the signed release. Coinkite takes private reports at [email protected] and may pay a bitcoin bounty. Its own disclosure history lists 30 security-relevant events from 2019 to 2026.

Public code did not catch the bug for five years, and we found no complete third-party audit. Transparency scores 78, behind Trezor (88).

What Coldcard does about scams

Coldcard handles only bitcoin, so there are no token approvals for drainersDrainerA malicious website or script that tricks a crypto user into signing a transaction or approval that lets attackers empty the wallet.More in the glossary to exploit. It parses each transaction and shows outputs, amounts and change addresses on its own screen, so a compromised computer cannot change where your coins go without you seeing it. Scam protection scores 85. It pairs well with a watch-only wallet such as BlueWallet on your phone.

How to stay safe with a Coldcard

1. Check when your seed was created. If it was on affected firmware, install fixed firmware, make a new seed and follow Coinkite's migration guide, testing with a small amount first.
2. Verify each firmware download's SHA-256 hash and signature before installing it.
3. Add a strong, unique passphrase for meaningful amounts, and back it up separately.
4. Consider multisigMultisigA crypto wallet that needs approval from several keys to move funds, for example any 2 of 3, rather than from a single key.More in the glossary across two brands, so one maker's flaw cannot empty the wallet.
5. Coinkite support never asks for seed words, passphrases or dice rolls.

How we scored it

Scam protection (85) and the company record (80) are Coldcard's strongest factors: careful on-device checks and a long-standing company with no data leaks we found. The security record (30) is the weakest, because a key-generation bug in its own firmware let attackers take more than 1,300 BTC, and victims have not been repaid. It is the 2026 flaw, not the design, that pulls Coldcard down to 65, level with Bitcoin.com Wallet and below Trezor (83).