Coldcard Firmware Flaw Enables $70M Bitcoin Theft in 41 Minutes
An attacker siphoned 1,082.65 BTC—worth roughly $70.2 million—from 1,196 addresses in a 41-minute sweep on July 30, 2026, according to Galaxy Research, which traced the drain to a longstanding firmware defect in Coinkite's Coldcard hardware wallets. The root cause is a March 2021 integration error that routed seed generation through MicroPython's deterministic Yasmarang pseudorandom number generator instead of the STM32 chip's hardware RNG. Security firm Block found that the `libngu` library checked only whether the `MICROPY_HW_ENABLE_RNG` macro existed, rather than whether it was set to one, binding the build to a fallback seeded from the device UID and timer registers with no further entropy collected.
Coinkite estimated effective entropy at approximately 40 bits on the Mk3 and about 72 bits on the Mk4, Mk5, and Q—well below the 128 bits required by a standard 12-word BIP-39 seed. Block noted that an attacker who can pin down a device's UID, boot timing, and prior RNG-call history can reproduce candidate output streams offline and validate seeds by deriving their addresses against public blockchain data. The company shipped emergency firmware on July 31, but patching does not retroactively heal an already-generated seed; affected owners must create a new wallet on updated firmware and migrate funds, since restoring the old seed carries the weakness forward. Vulnerable firmware tracks include Mk2 and Mk3 versions 4.0.0–4.1.9, Mk4 and Mk5 builds prior to 5.6.0, Q firmware before 1.5.0Q, and edge builds below 6.6.0X (and 6.6.0QX for Q). Users who generated a seed from at least 50 fair, independent, private dice rolls, or who protect it with a strong unique BIP-39 passphrase, are considered safe from this specific bug.
The incident underscores how a single build-system misconfiguration can silently downgrade cryptographic guarantees for years across multiple device generations. Anyone running exposed firmware should patch immediately, generate a fresh seed on updated hardware, and transfer balances to new addresses—then verify no residual exposure remains with a thorough privacy checkup. Reviewing the strength of stored credentials and recovery phrases via a password checker is a sensible secondary step, and operators managing custodial infrastructure should audit device provenance and firmware versions before the next on-chain sweep makes headlines.