
Zcash has completed a two-phase emergency upgrade to fix a critical flaw in its Orchard shielded pool, a vulnerability that went undetected for four years and could have enabled unlimited undetectable counterfeit ZEC within the pool. The swift response stabilized the network and helped reverse a sharp sell-off that saw ZEC’s price fall by roughly 50% before beginning to recover.
How the Vulnerability Was Discovered
The issue was identified on May 29, 2026, by security researcher Taylor Hornby during a protocol audit commissioned by Shielded Labs. According to the organization’s disclosure, Hornby found a “soundness” bug in Zcash’s Orchard zero-knowledge proof circuit—specifically, an under-constrained component in the Orchard Action circuit that could allow invalid state transitions and the theoretical creation of undetectable counterfeit ZEC within the shielded pool. Shielded Labs said the discovery was aided by a custom analysis suite and an AI model, and that Hornby produced a working proof-of-concept in a local test environment.
While the bug was severe in theory, Zcash’s internal turnstile accounting—which tracks value moving into and out of the shielded pool—showed no evidence of unauthorized value creation on the live network, according to Shielded Labs. However, because of Orchard’s privacy properties and the nature of the flaw, the group acknowledged there is no definitive cryptographic method to determine whether the vulnerability was exploited before the fix. The flaw had been present since Orchard’s activation in May 2022.
Emergency Response and Network Fix
Zcash’s developers moved quickly with a two-step remediation. First, an emergency soft fork via Zebra 4.5.3 was activated at block 3,363,426 on June 2, temporarily disabling all Orchard transactions to remove the attack vector while a permanent patch was finalized. Transparent and Sapling transactions continued uninterrupted, according to the Zcash Foundation.
The permanent fix arrived with the NU6.2 hard fork at block 3,364,600 on June 3, deployed via Zebra 5.0.0. This upgrade introduced a corrected circuit and a new verifying key, patching the flaw and re-enabling Orchard transactions. Josh Swihart, CEO of Electric Coin Company, later posted on June 7 that the fix was complete and the network secure.
Market Impact and Recovery
The incident triggered extreme volatility. ZEC rose from $544 on June 2 to $603 on June 3 and reached $624 on June 4 before plunging to $309 on June 5, a drawdown that erased more than $3 billion in market value, according to a timeline compiled by the BitMEX Blog. Sentiment was further pressured on June 4 when Arthur Hayes said he had exited his ZEC position, citing macro considerations.
Swihart’s June 7 update, along with transparent disclosures from Shielded Labs and the Zcash Foundation, helped restore confidence. As of publication, ZEC traded around $430, recovering from the lows recorded after the vulnerability’s disclosure, according to TradingView data.
What It Means for Zcash
The swift, coordinated response across the Zcash ecosystem contained a high-severity risk and restored core functionality to the Orchard shielded pool. At the same time, the episode underscores a long-standing challenge for privacy-focused cryptocurrencies: the same features that protect user privacy can complicate forensic verification when assessing potential exploits. Going forward, Zcash’s developers and community face the task of reinforcing assurance around shielded pools while maintaining the project’s privacy guarantees.

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