1h ago
ZEC Plunges 56% in a Day as Orchard Privacy Flaw Sparks Supply Integrity Fears
By Zhou, ChainCatcher
On June 5, privacy-focused cryptocurrency Zcash (ZEC) suffered a single-day drop of more than 56%, wiping out nearly two months of gains and briefly erasing about $5 billion in market value. Derivatives data shows roughly $100 million in 24-hour liquidations across ZEC contracts. Long liquidations exceeded $760 million, ranking behind only BTC and ETH.
The selloff was linked to disclosure of a zero-knowledge proof vulnerability that had existed for roughly four years in Zcash's newest private transaction pool, Orchard. In theory, the bug could allow an attacker to mint unlimited ZEC while remaining hidden by the pool's privacy protections. The issue was permanently fixed via a hard fork on June 3. Even so, Orchard's privacy design makes it impossible to provide cryptographic proof that the flaw was never exploited during the period it existed, fueling market doubts about ZEC's historical supply integrity.
BitMEX co-founder Arthur Hayes said he exited his entire ZEC position, while on-chain data also showed large short positions booking sizable gains, further pressuring sentiment.
How the flaw worked and how it was found
Orchard is Zcash's third-generation privacy layer, launched in May 2022. The vulnerability stemmed from insufficient constraints on an element inside the circuit. An attacker could feed false inputs into elliptic curve multiplication while still passing circuit verification, enabling unlimited counterfeit ZEC to be created within Orchard. Because of Orchard's privacy properties, such minting would leave no externally observable on-chain traces.
According to reports, independent security researcher Taylor Hornby identified the issue on May 29. Shielded Labs, an independent security organization, had engaged Hornby in April to conduct a focused audit of the Zcash protocol.
On May 28, Anthropic released Claude Opus 4.8. The next day, Hornby integrated it into a customized AI audit framework, performed targeted analysis of the Orchard circuit, and found the vulnerability. He also built a complete exploit in a local test environment to confirm that infinite minting was technically feasible. That night, he reported the issue to the Zcash Open Development Laboratory (ZODL).
ZODL engineers confirmed the issue within hours and moved into emergency response. On the morning of June 2, Zcash pushed an emergency soft fork via Zebra 4.5.3, temporarily disabling all Orchard transactions. At 12:05 p.m. Beijing time on June 3, mainnet completed the NU6.2 hard fork at block height 3,364,600, activating the patched circuit and closing the vulnerability. About five days elapsed from discovery to the hard fork.
The Zcash Foundation said this marked the second protocol upgrade triggered by a security issue since Zcash launched in 2016. It added that there are no known exploits, the network's total supply safeguard confirmed the integrity of total supply, and user privacy, as well as Sapling and transparent transactions, were unaffected.
Post-fix: anxiety persists
Despite the patch, a key concern remains: if forged funds were never moved into the transparent pool, today's tooling cannot detect anomalies on-chain. In other words, the conclusion of "total integrity" is based on observable data rather than cryptographic proof. Since the flaw has existed since May 2022, it cannot be definitively ruled out that it was exploited at some point.
Shielded Labs said exploitation is unlikely, citing three points: the bug went undiscovered for years, suggesting a very high technical barrier; it was surfaced through proactive auditing rather than accidental exposure; and the patch window was extremely short. Even so, the statement underscores that the risk cannot be disproven.
To narrow this gap, Shielded Labs said it is working with multiple developers on upgrade proposals, including new privacy pools and mandatory "turnstile" accounting checks for any tokens exiting Orchard, allowing public verification of supply integrity. A proposal is expected next week and would require community governance approval.
Crypto investor Simon Dedic argued the episode is shifting perceptions in two ways: privacy can be a protocol risk, not just a benefit; and AI-assisted auditing lowers the bar for discovering major vulnerabilities, raising the security-audit burden across crypto.
On-chain analyst Haotian said the core issue is "unclear explanations." He noted that Shielded Labs' proposed round-trip audit approach can only show that current supply is below the amount ever deposited into the pool, and still cannot account for potential historical hidden losses. He also pointed to a structural tension between verifiable supply and privacy black boxes, a dilemma that ZEC cannot easily resolve.
Panic accelerates the selloff
While the technical fix is in place, markets appear to have reacted to the full implications of the disclosure. On June 5, Zcash founder Zooko Wilcox, Shielded Labs, and Hornby jointly published a detailed write-up describing exploitability, the feasibility of infinite minting, and the inability to cryptographically prove the flaw was never used due to Orchard's privacy features. The publication intensified market fear.
That same day, Hayes confirmed he had sold all ZEC. He said the probability of malicious minting is extremely low but cannot be formally ruled out at the cryptographic level. In his view, privacy as a value proposition requires "perfect security," not "probabilistic security." He added he may consider buying back at lower prices if later assumptions prove wrong.
Hayes had previously been one of ZEC's most vocal proponents, at times describing it as his second-largest personal holding and suggesting ZEC could reach 10% of BTC's price, calling the earlier rally a move with "significant upside potential." His public exit weighed on sentiment.
On-chain analysts said that as ZEC fell below $400, a 3x leveraged short opened by Garrett Jin at $626.47 was showing tens of millions of dollars in unrealized gains. Some market participants argued the plunge cannot be attributed solely to the vulnerability. Crypto KOL DaShiBro said the prior rally had already shown signs of large capital inflows, and the vulnerability headline may have simply provided an exit catalyst, with heavy spot selling the more immediate driver. He added that a "strong-consensus blue chip" with a $12 billion market cap losing $6 billion in one day illustrates how hard consensus is to build in crypto, how easy it is to break, and how long recovery could take.