On June 5, Zcash founder Zooko Wilcox disclosed on X that security researcher Taylor Hornby had discovered a critical forgery vulnerability in the Zcash Orchard privacy pool on May 29. The bug theoretically allows an attacker to bypass system restrictions and mint unlimited fake ZEC tokens. Due to Orchard's cryptographic properties, such an attack is extremely hard to detect through conventional means. Worse, the vulnerability had existed since Orchard's launch in May 2022 — over four years.
AI-Powered Audit: Opus 4.8 Generated a Full Exploit
The finding used the latest AI-assisted security audit techniques. Shortly after Anthropic released the Opus 4.8 model on May 28, Taylor Hornby applied it to a targeted review of the Orchard circuit. Using Opus 4.8, he wrote a complete exploit program. Testing in a local regtest environment, the program produced unlimited, undetectable fake ZEC. Running the same tool on Zcash mainnet would have yielded the same result. The root cause is an under-constrained component in the Orchard circuit — an attacker can feed arbitrary wrong values into an elliptic curve multiplication check, and the check still passes. Compounding the issue, Orchard's privacy features and the bug's nature make it cryptographically impossible to determine whether it was exploited before being patched.
Market Panic: ZEC Drops Over 30% in One Day
The news triggered a sharp sell-off. Coingecko data shows ZEC plunged over 30% within 24 hours. Despite Zooko Wilcox's assertion that exploitation is unlikely, investors remain unconvinced. Zooko argued the bug had escaped many cryptographers' scrutiny for years, the discovery was a targeted search (not an accidental find), Taylor used cutting-edge AI tools available only to white-hat researchers, and the Zcash ecosystem patched quickly, shrinking the window of exploitability.
Community Split: Arthur Hayes Sells, Shielded Labs Proposes Upgrade
Opinions diverge on whether the bug was ever exploited. Helius CEO Mert said that while short-term proof is elusive, future turnstile activation or migration to a new verifiable privacy pool could determine if forgery occurred. He also noted Zcash's increasing use of advanced tools and external security auditors. BitMEX co-founder Arthur Hayes took the opposite view. In a post on X, he confirmed he had liquidated his entire ZEC position. "While the chance of malicious minting is extremely low, it's impossible to formally prove using cryptography," Hayes wrote. "The claim of protecting privacy from AI, governments, and big tech demands perfection, not low probability." He left the door open to repurchasing at a lower price if disproven.
To restore confidence, Shielded Labs — a non-profit core development organization focused on Zcash — announced it is collaborating with other Zcash developers on a network upgrade. The upgrade aims to let anyone verify the integrity of Zcash supply and "prove" that no forged ZEC exists in the Orchard pool. It involves deploying a new shielded pool and enforcing a "turnstile accounting" mechanism on all Orchard pool tokens. Details are expected next week. Separately, Shielded Labs launched a project to formally verify the Orchard circuit and write a mathematical proof that no undiscovered vulnerabilities remain.