Zcash Orchard Pool Counterfeiting Vulnerability
Summary
A critical soundness vulnerability in Zcash's Orchard shielded pool was discovered on May 29, 2026 by security engineer Taylor Hornby using Anthropic's Opus 4.8 AI model. The flaw, present since the Orchard pool's activation in May 2022, could have allowed a malicious prover to generate unlimited counterfeit ZEC undetectably within the shielded pool. An emergency soft fork and subsequent NU6.2 hard fork patched the vulnerability by June 3, 2026, prior to public disclosure on June 5, 2026, after which ZEC declined approximately 38% in 24 hours.
Connected Entities
1 entities · 10 linked investigationsTimeline(10 events)
2022-05-01
Orchard shielded pool activated via Zcash NU5 network upgrade; vulnerability introduced in halo2_gadgets scalar multiplication gadget.
Zcash Foundation / CoinDesk2026-04-01
Shielded Labs engages Taylor Hornby as a security engineer to conduct proactive protocol vulnerability research.
CoinDesk2026-05-29
Taylor Hornby discovers the Orchard circuit soundness vulnerability using Anthropic's Opus 4.8 model and a custom AI auditing harness. Hornby constructs a working exploit generating unlimited counterfeit ZEC in a local regtest environment. Responsible disclosure made to ZODL core engineers the same evening.
The Block / CoinDesk2026-05-31
Private coordination with miners, exchanges, and node operators begins in preparation for emergency network response.
Zcash Foundation2026-06-02
Emergency soft fork activates at Mainnet block height 3,363,426 (approximately 02:00 UTC) via Zebra 4.5.3, disabling all Orchard-containing transactions and blocks.
Zcash Foundation2026-06-03
NU6.2 hard fork activates at Mainnet block height 3,364,600 (00:05 EDT) via Zebra 5.0.0, re-enabling Orchard with corrected circuit logic and a new consensus rule rejecting non-canonical proof sizes.
Zcash Foundation2026-06-05
Public disclosure of the vulnerability by Shielded Labs. ZEC declines approximately 37.8-38% in 24 hours, falling from approximately $635 to a low of approximately $309.
The Block / CoinDesk / Decrypt2026-06-05
Arthur Hayes, BitMEX co-founder, publicly discloses he has liquidated his entire ZEC position, citing the irresolvable uncertainty about whether counterfeiting occurred prior to the fix.
CoinDesk2026-06-05
Shielded Labs proposes a new network upgrade to create a fresh shielded pool with turnstile accounting on all existing Orchard coins to provide provable supply integrity.
The DefiantDecision Log
- hash: CEQifRMAqaDbTtEsCwPP4VPEDZpZkzDDwXQWrMVuYHDR
This investigation is cryptographically anchored to the Solana blockchain and source URLs are archived via the Internet Archive.
model: claude-sonnet-4-6
generated: 6/30/2026, 12:15:04 PM
last updated: 6/30/2026, 12:15:15 PM
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