A random number generation flaw in Coldcard firmware may have left thousands of Bitcoin addresses with substantially weakened seeds. Researchers have linked the bug to suspected thefts totaling $88.6 million across 4,585 blockchain addresses, although the connection has not been computationally confirmed for every wallet.
The affected firmware generated seeds with reduced entropy, potentially allowing an attacker to reproduce candidate seeds offline, derive their Bitcoin addresses, and compare them with public blockchain data. Coldcard owners who created seeds on vulnerable releases should install the patched firmware, generate a new seed, and transfer their funds, as updating the device does not repair an existing seed.
Weak randomness may have exposed wallet seeds
BleepingComputer reported that an integration error caused affected Coldcard firmware to route seed generation through MicroPython’s deterministic Yasmarang pseudorandom number generator instead of the device’s STM32 hardware random number generator.
The fallback generator relied on the device’s microcontroller identifier and system timing values rather than fresh cryptographic entropy. Researchers said the feasibility of reproducing a seed would depend on factors including the device identifier, boot timing, previous RNG calls, and the cost of testing candidate seeds.
According to The Hacker News, Galaxy Research initially identified a 41-minute sweep on July 30 involving 1,196 addresses and approximately 1,082.65 BTC, valued at $70.2 million at the time. Two additional suspected waves later raised the estimate to 1,367.05 BTC, worth about $88.6 million, across 4,585 addresses.
Galaxy based its findings on transaction patterns and on-chain analysis. Researchers have not publicly reconstructed a victim’s seed and matched it to a drained address, and Galaxy has not computationally confirmed that every identified address was generated by vulnerable Coldcard firmware.
Which Coldcard devices are affected
Exposure depends on the firmware used when the seed was generated. Reported affected versions include Mk2 and Mk3 firmware from the 4.0.x and 4.1.x release lines, Mk4 and Mk5 standard firmware earlier than 5.6.0, and Q firmware earlier than 1.5.0Q.
Certain Edge releases before 6.6.0X for Mk4 and Mk5 devices or 6.6.0QX for Q devices are also vulnerable.
Coinkite released emergency firmware for the affected products on July 31. Restoring an old seed on patched firmware or importing it into another wallet carries the weakness forward, which is why Coinkite recommends generating a replacement seed.
Seeds supplemented with at least 50 fair, independent, and private dice rolls are not considered at risk from this flaw alone. Coinkite also said TAPSIGNER, OPENDIME, and SATSCARD products are unaffected because they use different codebases.
What affected wallet owners should do
Before migrating, owners should verify their existing backup and install the appropriate firmware update. They should securely record the replacement seed, confirm the receiving address on the device, send a small test transaction, and move the remaining balance only after the test is confirmed.
A BIP-39 passphrase may reduce the risk in some configurations, but Coinkite still advises users to replace the underlying seed rather than rely on the passphrase as a permanent defense. Multisignature configurations may offer protection only when the signing quorum does not consist entirely of affected devices.
The suspected thefts show why patching firmware cannot always reverse a cryptographic failure. For affected Coldcard owners, the immediate priority is to retire potentially weak seeds and move funds to a wallet generated with patched firmware.
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