Zcash developers are moving to seal a critical vulnerability in the network's Orchard shielded pool. The fix arrives via the Ironwood hard fork (NU6.3), scheduled to activate around July 28, 2026, at block height 3,428,143. The upgrade closes a soundness flaw that could have allowed attackers to create coins out of thin air or double-spend transactions.
The soundness flaw in Orchard
The bug lives in the Orchard shielded pool, Zcash's most private transaction system. A soundness flaw means the network's math broke down — someone could have generated fake proofs and minted coins without actually burning value. Developers have kept details under wraps to avoid giving bad actors a head start, but they confirmed the issue is serious enough to require a mandatory network upgrade.
Orchard was introduced in 2022 as a major privacy upgrade. It uses Halo 2 proofs, which don't require a trusted setup. The flaw undermines the core guarantee that shielded transactions are sound. Users who rely on Orchard for privacy or value transfer need to update their software before the fork.
Ironwood hard fork details
The Ironwood upgrade is a consensus change — every node must run the new code or risk being left behind on a dead chain. Activation is set for block 3,428,143, which should arrive around July 28. The exact date depends on block times, but developers expect it to hold.
This is not a contentious fork. The Zcash community and the Electric Coin Company, which leads development, are unified behind the fix. No new features are bundled in; the sole purpose is to patch the Orchard soundness hole.
Zakura Node: faster sync for the fix
A new node implementation called Zakura Node is already backing the fix. Built for speed, it can sync the entire Zcash blockchain in about four hours — a fraction of the time older clients take. That matters because the hard fork requires all nodes to upgrade. Faster sync lowers the barrier for new users and makes it easier for existing operators to spin up fresh nodes.
Zakura Node is not replacing the reference client, but it gives the network a second, faster option. Developers say it passed the same consensus tests and is ready for production use.
What users need to do
Anyone running a Zcash node must upgrade to a version that includes the Ironwood rules before the fork. Wallet users who rely on third-party services should check that their provider has updated. Exchanges and mining pools need to coordinate their upgrades to avoid chain splits.
The Electric Coin Company has published a timeline: testnet activation is expected a few weeks before mainnet. Users can test their setups then. The deadline is block 3,428,143 — no grace period.
