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/DISPATCH · 2026-08-11

Coinkite Coldcard Firmware Flaw: $110M Bitcoin Theft Breaks the Cold-Wallet Myth

In August 2026 a RNG defect in Coinkite Coldcard firmware let attackers reconstruct private keys without physical access and steal about $110–130 million in Bitcoin. The incident undercut the cold-wallet security myth and drove a four-month-high $853 million weekly net inflow into U.S. spot Bitcoin ETFs.

In August 2026, Canadian hardware-wallet vendor Coinkite disclosed an RNG defect in Coldcard firmware. Attackers reconstructed private keys at scale without physical access and stole about $110–130 million in Bitcoin. The incident undercut the assumption that cold wallets equal absolute safety and drove a four-month-high $853 million weekly inflow into U.S. spot Bitcoin ETFs as long-term holders moved from self-custody to regulated institutional products.

Incident Overview

Galaxy Research reported that as of 3 August attackers had moved more than 1,755 BTC from about 5,000 affected wallet addresses, worth about $110 million at then-market prices; some later tallies put losses near $130 million. Coinkite confirmed the flaw, shipped patched firmware, and told all Coldcard users to upgrade immediately. The engineering root cause sits in firmware 4.0.0, shipped March 2021: a build-config mistake silently disabled the hardware true random number generator (TRNG), so devices used a predictable software PRNG to generate BIP-39 mnemonics.

Affected devices include Mk2 and Mk3 models and multiple firmware versions between 4.0.1 and 4.1.9. The vendor stopped shipping affected lots and destroyed unsold inventory. Customers were told to move funds to wallets with newly generated mnemonics or to devices reset after the firmware fix.

Technical Details

The crypto algorithms were not broken. The failure is an entropy-source engineering error at key generation. Coldcard is designed to seed from the STM32 on-chip hardware RNG, but firmware 4.0.0's compile config bypassed the hardware RNG call and fell back to a predictable software PRNG.

Yu Jianing, co-chair of the Blockchain Committee of the China Communications Industry Association, said effective entropy on some models collapsed to about 40 bits. Attackers need no firmware reverse engineering and no physical access: they enumerate candidate seeds on ordinary computers, match them against public on-chain address balances, and recover private keys at affordable compute cost. Recovered keys sign transfers from anywhere, bypassing the usual cold-wallet offline-custody assumption.

Stealth widened the blast radius. Affected mnemonics look identical to correctly generated ones, and on-chain balances look legitimate, so users had almost no way to self-detect before disclosure.

Impact Assessment

Remediation

References