Editor | Grok et al.
Zcash is a well-known privacy coin in the crypto space, renowned for its robust shielded transactions feature. These transactions utilize Zero-Knowledge Proof (ZKP) technology, allowing users to transfer funds without revealing specific amounts, addresses, or other details, thus protecting their privacy.
In April to May 2026, ZEC saw a significant pump, skyrocketing by as much as 150%, with its market cap hitting the multi-billion dollar level. As global regulations tighten and on-chain transparency increases, users are growing more concerned about 'seizable/monitorable' assets. Zcash's shielded pools (especially the Orchard pool) offer optional privacy protection, attracting investors looking for 'censorship and seizure-resistant' assets. Institutions like Multicoin Capital have explicitly positioned ZEC as a return to cypherpunk ideals, emphasizing that in the era of on-chain finance, privacy will be a core demand. This narrative resonates with the broader market environment (such as discussions around potential wealth taxes), driving capital inflows.
Cypherpunk Technologies (backed by Winklevoss) has surged, having significantly bought into ZEC, holding about 1.7%-2% of the total supply, becoming a major institutional holder. The Winklevoss twins (founders of Gemini) have long supported Zcash, making several donations and increasing their holdings through affiliated entities. Foundry Digital launched an institutional-grade ZEC mining pool; Maelstrom Fund (linked to Arthur Hayes) has also taken positions. Grayscale has submitted an application to convert the Zcash Trust into the first privacy coin spot ETF in the US (potential ticker ZCSH). If approved, this will provide a compliant entry for institutional funds, expected to attract billions.
However, recently, a significant vulnerability was discovered in Zcash's latest privacy pool, Orchard, triggering intense market volatility. The team swiftly took emergency measures by temporarily disabling related transactions through a soft fork, and then completing the fix via a hard fork. The entire process found no evidence of actual exploitation, but the nature of privacy design also posed challenges for supply integrity verification. This article compiles a detailed timeline based on official announcements, developer forums, and reliable media reports, and explains key professional terminology.
What is the Orchard pool? Why is it so important?
Orchard is the latest shielded pool launched by Zcash in May 2022 through the NU5 network upgrade. Unlike the earlier Sprout and Sapling pools, Orchard is based on the Halo 2 proof system, an advanced zero-knowledge proof technology that does not require a trusted setup, significantly enhancing privacy efficiency and scalability.
At the time of the vulnerability disclosure, the Orchard pool held over 4.5 million ZEC, representing a significant proportion of the total supply, worth billions. It is the core of Zcash's privacy architecture, but the complex zero-knowledge circuits also present long-term auditing challenges.
Nature of the vulnerability: Detailed explanation of the Soundness Bug
This vulnerability is a soundness (健全性) bug located in the Orchard Action circuit (the zero-knowledge proof circuit handling shielded transaction actions). Specifically, it is an under-constrained issue in the circuit that allows the generation of invalid but network-accepted proofs.
In simple terms: in a zero-knowledge proof system, 'soundness' ensures that only legitimate transactions can pass verification. If soundness fails, an attacker could theoretically forge proofs, achieving double-spending within the Orchard pool or minting fake ZEC without detection. This vulnerability has been lurking since the Orchard's launch in 2022.
It's worth noting that due to Zcash's turnstile mechanism (a cross-pool accounting check system), even if anomalies occur within the Orchard pool, the total supply will not be infinitely inflated — the turnstile will limit the value flowing out of the pool to not exceed the value flowing in. However, the privacy features make it difficult for outsiders to 100% cryptographically prove that the pool has never been exploited.
Vulnerability discovery process (May 29)
On May 29, 2026: Independent security researcher Taylor Hornby (former security engineer at Electric Coin Company, commissioned by Shielded Labs for protocol auditing) discovered the vulnerability during a routine audit. He utilized Anthropic's latest released Claude Opus 4.8 AI model to assist in analyzing the circuit and successfully built a complete exploit in a local test environment, generating unlimited forged ZEC.
Hornby privately disclosed the findings to the Zcash Open Development Lab (ZODL) and the Zcash Foundation on the same day. The team immediately initiated an emergency response procedure, coordinating miners, exchanges, and node operators.
Emergency response phase one: soft fork to disable Orchard (June 1-2)
Private coordination began on the evening of May 31. The first soft fork attempt encountered deployment coordination issues, and the team iterated quickly.
On June 2, 2026 (around UTC 2:00, mainnet block height 3,363,426): Emergency updates like Zebra 4.5.3 were deployed, activating an emergency soft fork. The network required nodes and miners to reject all transactions and blocks containing Orchard actions, temporarily disabling Orchard transactions (Sapling and transparent transactions were unaffected). This move aimed to prevent potential exploitation during the repair period.
During the transition period, there were brief instabilities in the network, resulting in multiple competing chains and orphan blocks. Wallets like Cake Wallet temporarily faced limitations on ZEC functions, but the overall chain continued to operate.
Emergency response phase two: NU6.2 hard fork fix (June 3)
On June 3, 2026 (around EDT 00:05, mainnet block height 3,364,600): NU6.2 hard fork activated, supported by Zebra 5.0.0. This upgrade deployed the corrected Orchard Action circuit, introduced new verifying keys (per-circuit verifying key), and re-enabled Orchard transactions.
From disclosure to full recovery took only about 5 days, marking the second security-driven protocol upgrade in Zcash's history. ZODL and the foundation confirmed: no loss of funds, no unauthorized value creation, and the turnstile mechanism detected no anomalies, ensuring user privacy and fund security.
Market reaction and community impact
Following the disclosure of the vulnerability, the ZEC price experienced extreme volatility, plunging nearly 40%-50% from its peak, resulting in a market cap evaporation of billions. Some well-known figures (like Arthur Hayes) liquidated their positions, and short selling in derivatives surged. However, as the fix was completed, the price stabilized somewhat.
Community discussion points include: the impact of the privacy pool pause on decentralization narratives, the role of AI in security audits, maintenance challenges of dual-node implementations (zcashd + Zebra), and the upcoming NU7 upgrade (faster blocks, shielded asset support, etc.). Shielded Labs also proposed further upgrades to enhance supply verifiability with new pools and turnstiles.
This incident highlights the balancing act of privacy coins between ultimate privacy and auditability. The swift, professional response from the Zcash team is commendable — efficiently coordinating multiple parties to complete complex upgrades in a short time, a high-efficiency case in crypto history.
But the double-edged sword of privacy design reminds the industry: complex zk systems need continuous reinforcement of formal verification, multi-party audits, and AI-assisted tools. Zcash, as a pioneer in the privacy space, will see its future node migration (transition to Zebra), governance optimization, and institutional opportunities (like potential ETFs) determine its long-term trust rebuild.
A landmark case for AI-assisted security auditing
A notable detail in the Zcash Orchard pool soundness vulnerability incident is that security researcher Taylor Hornby successfully discovered and validated this significant defect lurking for nearly 4 years, aided by Anthropic's latest Claude Opus 4.8 AI model. This process not only highlights AI's powerful potential in complex cryptographic auditing but also provides important insights for the entire blockchain security field.
Anthropic officially released Claude Opus 4.8 on May 28, 2026, which is the latest flagship model in its Opus series. This model achieves cutting-edge levels in coding capabilities, agentic tasks, long-context reasoning, and professional knowledge work, supporting up to a 1M token context window, and introduces new features such as 'Dynamic Workflows' and 'effort controls'.
Hornby, as an independent security engineer commissioned by Shielded Labs, began a continuous review of the Zcash protocol in April 2026. On the day following the release of Claude Opus 4.8 (May 29), he combined it with a custom AI auditing framework for targeted reviews of the Orchard Action circuit.
With the model's powerful code understanding and complex reasoning abilities, Hornby not only pinpointed the under-constrained issues in the circuit but also successfully wrote a complete exploit. In a local regtest testing environment, this exploit was capable of generating unlimited, undetectable forged ZEC, which were indistinguishable from legitimate ZEC within the privacy pool.
This process integrated traditional security research methods with the latest AI tools: Opus 4.8 helped analyze the elliptic curve math verification logic, generate test cases, and assist in constructing proof generation code, significantly speeding up the cycle from theoretical discovery to practical verification. Hornby responsibly disclosed it privately to the Zcash Open Development Lab (ZODL), avoiding any mainnet risks.
This incident is regarded as a landmark case for AI-assisted security auditing. In recent years, despite Zcash undergoing multiple manual audits and formal verifications, the complex zero-knowledge circuits (especially the Orchard implementation based on Halo 2) still have blind spots that are difficult for humans to cover comprehensively. The involvement of Claude Opus 4.8 demonstrates the unique advantages of cutting-edge large models in handling massive code and identifying subtle constraint deficiencies.
The application of Claude Opus 4.8 in the discovery of the Zcash vulnerability marks a shift of AI from being an auxiliary tool to a core security force. This not only accelerated the response (from disclosure to fix in just a few days) but also established a new paradigm of 'AI white hats' for the crypto industry. In the future, with more cutting-edge models like the Anthropic Mythos series, the efficiency of blockchain protocol audits is expected to significantly improve.