Overview
- The flaw was found by auditor Taylor Hornby on May 29, 2026 and was a soundness bug in Orchard’s zero‑knowledge proof circuit that could theoretically let an attacker create undetectable counterfeit ZEC.
- Developers executed a two‑stage emergency fix that first disabled Orchard transactions and then deployed the NU6.2 hard fork, which corrected the circuit and re‑enabled shielded transfers.
- Because Orchard hides transaction details with zero‑knowledge proofs, teams say there is no cryptographic way to prove whether the bug was ever exploited even though no on‑chain evidence of inflation has been reported.
- The Ironwood proposal would create a new repaired shielded pool, close the legacy Orchard pool to new deposits, and use Zcash’s turnstile accounting plus formal audits and verification so node operators can independently check circulating supply.
- The disclosure triggered a roughly 50% price plunge and large withdrawals before a partial rebound, and developers now face coordinated testing, wallet and exchange migration, and formal verification work to rebuild user trust.