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Zcash Orchard Counterfeit Vulnerability

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Summary

On June 5, 2026, Shielded Labs publicly disclosed a critical four-year-old soundness bug in Zcash's Orchard shielded pool that, if exploited, could have allowed unlimited undetectable counterfeit ZEC minting. The vulnerability was discovered on May 29, 2026 by security researcher Taylor Hornby using AI-assisted auditing tools, silently patched via emergency hard fork on June 2, and cannot be definitively ruled out as having been exploited due to Orchard's inherent privacy architecture. ZEC fell approximately 38–50% in the 48 hours following public disclosure.

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Zcash Orchard Counterfeit Vulnerability
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Timeline(12 events)

May 2022

Zcash Orchard shielded pool activates on mainnet. The soundness vulnerability in the halo2_gadgets elliptic curve multiplication circuit is present from launch.

Shielded Labs disclosure

2026

SEC closes investigation into Zcash Foundation without enforcement action, removing a significant regulatory overhang.

CryptoTimes

April 2026

Shielded Labs engages security engineer Taylor Hornby for a targeted protocol security review of Zcash.

CoinDesk

28 May 2026

Anthropic releases Claude Opus 4.8, the AI model that Hornby would use the following day to identify the Orchard vulnerability.

BeInCrypto

29 May 2026

Taylor Hornby discovers the critical soundness vulnerability in the Orchard ZK proof circuit using AI-assisted auditing tools. He develops a working proof-of-concept exploit generating unlimited undetectable counterfeit ZEC in a test environment. Hornby immediately discloses to ZODL.

CoinDesk

June 2026

Emergency protocol patch activates at 22:30 EDT, disabling all Orchard-containing transactions at mainnet block height 3,363,426. ZODL releases zcashd v6.12.5.

CryptoTimes

3 June 2026

Hard fork network upgrade NU6.2 completes, re-enabling Orchard with the corrected circuit. Network experiences brief instability including a 25-block fork and 37 orphaned blocks during the switchover.

Crypto Economy

4 June 2026

ZEC trades at a high of approximately $635.

Decrypt

5 June 2026

Shielded Labs publicly discloses the vulnerability. ZEC falls approximately 38% in 24 hours to approximately $309, a decline of approximately 51% from the June 4 high. Arthur Hayes publicly liquidates his entire ZEC position.

CoinDesk

8 June 2026

Zcash developers propose the Ironwood network upgrade as a structural solution to supply integrity uncertainty. ZEC rebounds approximately 45% from post-disclosure lows.

CoinDesk

14 June 2026

Bloomberg publishes analysis characterizing the incident as illustrating the broad 'scale of AI-hacking threat' to cryptographic systems.

Bloomberg

15 June 2026

Zcash founder Zooko publishes explanation of how Ironwood's turnstile mechanism will function as a live supply audit during pool migration.

CryptoTimes
Provenance & Audit Trail

Decision Log

This investigation is cryptographically anchored to the Solana blockchain (3 events). 18 of 20 cited source URLs have an Internet Archive snapshot.

model: claude-sonnet-4-6

generated: 6/17/2026, 11:04:36 PM

last updated: 8/27/2026, 1:12:03 PM

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