Coldcard Vulnerability: AI found RNG-sabotage, multisig key rotation

A reported Coldcard vulnerability led to a theft on July 30, 2026: about 1,200 Coldcard wallets were drained in ~40 minutes, with attackers moving over 1,000 BTC to a controlled wallet. Crypto security researchers traced the root cause to a firmware integration build-configuration error that silently disabled Coldcard’s hardware random number generator (RNG). Instead, the firmware fell back to a deterministic pseudo-random generator seeded with attacker-predictable values (notably the device serial number and clock state). For older devices, the effective seed space dropped to roughly ~40 bits, enabling offline seed enumeration, address derivation, and blockchain matching without touching devices or using phishing. Casa co-founder Jameson Lopp says the bug highlights a changed threat model: vulnerability discovery economics now reward machines running against public security-critical code (including firmware and custody logic). He argues manual audits and one-off pentests are “photographs,” while attackers can rapidly iterate. In response, Casa claims it ran AI penetration testing more frequently using frontier models and an internal AI harness designed to reduce hallucination risk (discover → verify with exact code citations → report). Casa also describes defense-in-depth: automated review on every change, human review, test-first fixes, end-to-end testing, and, most importantly, a multisignature vault design. The key trading/operational takeaway for Bitcoin holders using affected hardware is that Coldcard vulnerability impacts individual keys; multisig should prevent fund loss as long as you rotate keys on fixed firmware and maintain quorum. Casa says it contacted affected clients with guidance: update firmware, regenerate seeds on fixed firmware, and rotate vault keys.