COLDCARD firmware generated weak seeds
Who is affected
Funds on seeds generated with the affected firmware can be found and swept remotely. Current firmware is fixed, but the risk remains for funds still held on old seeds.
What happened
A firmware build setting introduced in 2021 made COLDCARD devices generate seeds with a software random number generator instead of the hardware one. According to Coinkite, seeds created on the Mk4, Mk5 and Q carry about 72 bits of entropy rather than 128, and older Mk2/Mk3 firmware fared worse.
Attackers began guessing and sweeping affected wallets on 30 July 2026. Coinkite states the devices themselves were not hacked or remotely accessed: the weakness is in seeds that were already generated.
Affected are seeds generated on Mk4/Mk5 firmware before 5.6.0, Q firmware before 1.5.0Q, Edge firmware before 6.6.0X / 6.6.0QX, and Mk2/Mk3 firmware 4.0.1–4.1.9. Seeds built from 50 or more private dice rolls are not at risk from this bug.
What Coinkite advises:
- Install the fixed firmware before generating a new seed.
- Move funds to a newly generated seed, even if you use a strong passphrase — updating firmware does not repair an existing seed.
- Verify the new backup and a receive address on the device, send a small test transaction, then move the rest.
Firmware is the software that runs on a hardware wallet itself: it generates keys, shows transaction details on the screen and signs.
Read full definitionColdcard is an air-gapped hardware wallet for Bitcoin, made by Coinkite, that stores private keys offline and signs transactions without internet exposure.
A Random Number Generator (RNG) produces unpredictable numbers essential for cryptographic security in blockchain, such as generating private keys and nonces.
Read full definitionEntropy is the randomness used to generate secure cryptographic keys or seeds in blockchain and cryptocurrency systems.
Read full definitionA passphrase is an additional security layer for cryptocurrency wallets, acting as a 25th word in the BIP39 seed phrase, protecting access to hidden wallets.
Read full definitionA backup in cryptocurrency is a secure copy of a wallet's seed phrase or private keys. It enables recovery of funds if the original wallet is lost or damaged.
Read full definitionA wallet address is the public identifier others use to send you crypto. It is derived from a public key and is safe to share.
Read full definitionA test transaction is a small transfer sent before a large one to confirm the address, network and wallet setup work as expected.
Read full definitionSources
Independent reporting and research this entry was checked against.
Learn more
Guides on protecting yourself against this type of incident (Firmware vulnerability) and the glossary terms that describe it.
Can Hardware Wallets Be Hacked?
Hardware wallets are extremely secure, but not invincible. Understand the real risks and attack vectors.
Read GuideIs a Hardware Wallet Really Safe?
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Read GuideFirmware
Firmware is the software that runs on a hardware wallet itself: it generates keys, shows transaction details on the screen and signs.
Bootloader
A bootloader is a small program that initializes hardware and loads the main operating system or firmware on a device, often used in blockchain hardware wallets for secure startup.
Firmware Update
Firmware Update installs new low-level software on a hardware wallet to fix bugs, enhance security, or add features in cryptocurrency devices.
Cite this entry
WalletInsights. “COLDCARD firmware generated weak seeds”. Hardware wallet security incident tracker. Last verified October 26, 2026. https://walletinsights.io/en/security-incidents/coldcard-weak-seed-generation-2026/
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