Zcash Reveals Critical Orchard Shielded Pool Flaw That Could Have Enabled Unlimited ZEC Minting

Zcash has disclosed a critical vulnerability in its Orchard shielded pool that developers say could have allowed unlimited counterfeit ZEC to be created inside the privacy pool. The bug was found and patched within days, and Zcash-linked teams are now preparing an additional upgrade aimed at restoring certainty around supply integrity. The disclosure triggered a sharp market reaction, with ZEC dropping about 33% in 24 hours; BitMEX cofounder Arthur Hayes said he sold his entire ZEC position following the news. Zcash founder Zooko WilcoxO'Hearn said security researcher Taylor Hornby identified the issue on May 29, and an emergency fix was completed on June 2. The flaw had existed since Orchard launched in May 2022. Hornby demonstrated a working exploit in a local test environment that produced unlimited counterfeit ZEC while evading normal detection. Developers said the same approach could have been used on the live network before the patch. The root cause was described as a weakness in Orchard's cryptographic circuit. In practice, the system could be coerced into accepting invalid transaction data as valid, enabling new coins to be created within the shielded pool. Privacy Limits On-Chain Verification Beyond the technical severity, developers emphasized an auditing constraint unique to Orchard: because shielded pools obscure balances and transaction details, the network cannot cryptographically prove after the fact whether the vulnerability was exploited prior to the fix. Shielded Labs said there is currently no definitive way to demonstrate from blockchain data alone that counterfeit ZEC was never minted during the four-year window the bug existed, though it added that prior exploitation appears unlikely. The issue also raised questions about review coverage, having gone unnoticed through years of scrutiny by cryptographers and auditors. Shielded Labs said Hornby's finding came through a focused security initiative intended to surface hidden weaknesses before attackers could. Emergency Soft Fork and Follow-Up Upgrade After disclosure, engineers at the Zcash Open Development Lab coordinated a private response with miners and exchanges. An emergency soft fork disabled Orchard transactions on June 2 at block 3,363,426. A follow-on upgrade, NU6.2, re-enabled Orchard on June 3 at block 3,364,600 using a corrected circuit. During the pause, transparent transactions and Sapling transactions continued to operate. Uncertainty over whether counterfeit coins ever existed in Orchard remains the central concern. Orchard currently holds more than 4 million ZEC and represents the majority of coins held in Zcash's private pools. New Upgrade Proposal Targets Supply Integrity Shielded Labs said it intends to propose an additional network upgrade designed to remove the remaining uncertainty around Orchard's supply. The concept would create a new shielded pool and require all coins leaving Orchard to pass through "turnstile" accounting, enabling independent verification that no counterfeit ZEC exists. Developers said the full proposal will be published in the coming days. Market Fallout and Hayes' Exit Following the disclosure, ZEC gave up its weekly gains and fell roughly 33% over 24 hours, bringing its seven-day decline to about 25%. Arthur Hayes said he liquidated his entire ZEC position after reviewing the vulnerability. In a post dated June 5, 2026, he said that while unauthorized minting seemed unlikely, he could not cryptographically prove it never occurred, and that uncertainty undermined his investment thesis for privacy-focused assets. Hayes added he would consider re-entering ZEC if future evidence strengthens confidence in supply integrity. Disclaimer: This material is for informational and educational purposes only and does not constitute financial advice. Coin Edition is not responsible for losses arising from the use of any content, products, or services mentioned. Readers should exercise caution before taking any action related to the company.