Zcash disclosed a critical vulnerability in its Orchard shielded pool on 4 June that could have allowed an attacker to “undetectably create an unlimited amount of counterfeit ZEC within Orchard,” according to the disclosure from Zooko Wilcox, Jason McGee, and Taylor Hornby.
Security researcher Hornby found the flaw on 29 May during an AI-assisted audit using Anthropic’s Opus 4.8. The bug, an under-constrained element of the Orchard circuit, had been live since Orchard launched in May 2022.
Zcash’s remediation came in two stages. An emergency soft fork on 2 June temporarily disabled Orchard actions. The NU6.2 hard fork on 3 June restored Orchard with a corrected circuit and new verifying key. Sapling and transparent transactions operated normally throughout.
The Zcash Foundation said there was no evidence of unauthorized value creation and that the turnstile mechanism confirmed total supply remained intact. The disclosure also noted that Orchard’s privacy properties mean the network cannot cryptographically prove the flaw was never exploited before the fix.
ZEC fell from around $558 to $264 before stabilising near $320, crypto derivatives analytics firm Block Scholes said, describing it as a roughly 50% single-day drop.
