COLDCARD (Coinkite): firmware RNG bug made seeds regenerable offline

What happened

• 30 Jul 2026: first wave drained about 1,083 BTC from 1,196 addresses in 41 minutes (Galaxy Research). By 1 Aug Galaxy counted about 1,367 BTC (about USD 88.6M) from 4,585 addresses. Later secondary reports cite a Galaxy count of about 1,596 BTC.
• Root cause per Coinkite: “A firmware bug in affected releases caused weakened seed generation.” Block’s Bitcoin engineering and security teams, who reported it to Coinkite on 30 Jul, traced it to an “RNG integration error”: a check routed seed generation to a deterministic software generator based on the MCU identifier and timing instead of the hardware RNG. Affected: Mk2/Mk3 firmware 4.0.1 (March 2021) to 4.1.9; Mk4/Mk5 before 5.6.0 (Edge before 6.6.0X); Q before 1.5.0Q (Edge before 6.6.0QX). Coinkite says Mk4/Mk5/Q seeds have about 72 bits of entropy instead of 128.
• Attribution: no attacker identified. Galaxy noted a fixed 30 sat/vB fee and no change outputs, suggesting an automated tool.
• Response: Coinkite’s CEO first said there was “no evidence of a flaw”, then apologized. Coinkite destroyed unshipped units with affected firmware and told users to update and migrate to a new seed. Seeds with 50 or more private dice rolls are not considered at risk from this flaw alone.

Sources

• https://blog.coinkite.com/coldcard-mk3-seed-generation-warning/
• https://bleepingcomputer.com/news/security/coldcard-wallet-rng-flaw-likely-linked-to-88-million-bitcoin-theft

This is a brief: a short, sourced summary from our incident tracking. Full advisories add commands to check whether you are affected.