Zcash developers have finalized the consensus changes for the upcoming Ironwood upgrade, aiming for activation in late July at block height 3,417,100. The upgrade is intended to resolve a critical flaw in the Orchard shielded pool that could have enabled unlimited counterfeit ZEC creation.

Ironwood will introduce a new shielded pool, tighten supply enforcement through the existing turnstile mechanism, and block any new incoming transactions into the compromised Orchard pool. These updates are supported by formally verified zero-knowledge circuits and independent third-party security audits.

The Orchard Vulnerability: What Ironwood Addresses

The Orchard pool, launched in May 2022 as part of the NU5 upgrade, integrated the Halo 2 proof system and represented Zcash’s most advanced privacy layer. It relies on zero-knowledge proofs to conceal transaction values and participant identities without requiring a trusted setup.

However, a flaw identified in early 2026 exposed a weakness in the circuit design. An attacker exploiting it could have generated counterfeit ZEC without leaving any detectable on-chain evidence.

As a result, the total supply within Orchard was not strictly constrained by consensus. The same privacy features that protect user transactions also made unauthorized issuance effectively invisible—even to Zcash’s own developers.

The issue was uncovered through an AI-assisted external security review, prompting a quiet fix and coordinated disclosure ahead of the Ironwood rollout.

Turnstile Mechanism, New Pool, and Supply Assurance

Ironwood is being developed through a collaborative effort involving ZODL, Tachyon, Valar Group, the Zcash Foundation, and Shielded Labs, reflecting a multi-stakeholder governance approach.

At the core of the upgrade is a redesigned Orchard circuit that includes a mechanism to restrict outgoing payments within a pool while still allowing change outputs, preserving user privacy.

Once activated, this restriction will be permanently applied to the legacy Orchard pool. All new transactions will be redirected to the replacement pool, while constraints on the valueBalance field help enforce supply integrity.

The upgrade leverages the existing turnstile mechanism to ensure proper supply accounting. Any ZEC leaving the old Orchard pool must pass through the turnstile before entering the new pool, guaranteeing that the amount exiting cannot exceed the amount originally deposited.

This design ensures that the circulating supply remains bounded as intended. After migration, full nodes will be able to independently verify that no counterfeit ZEC has entered the new pool, restoring trustless supply validation at the protocol level.

The planned activation aligns with the end-of-support for zcashd at block height 3,417,100. Before mainnet deployment, the upgrade will undergo testnet validation, ecosystem coordination, and final audits. Wallet providers are expected to offer streamlined migration tools, and the new pool is designed to maintain compatibility with existing Orchard addresses, avoiding the need for key changes.