WuBlockchain
The Zcash Foundation has released Zebra 4.5.3 and 5.0.0 to address a critical soundness bug discovered in the Orchard Action circuit. The emergency response unfolded in two stages: Zebra 4.5.3 temporarily disabled Orchard actions via a soft fork at mainnet block height 3,363,426, while Zebra 5.0.0 activated the NU6.2 hard fork at block height 3,364,600 and re-enabled Orchard with the corrected circuit.
Why it matters
The Orchard protocol is the most privacy-preserving layer of the Zcash stack, underpinning shielded transactions that use zero-knowledge proofs. A soundness bug in the Action circuit could, in theory, allow an attacker to forge proofs and create unauthorized value — effectively a hidden inflation vector. The Foundation confirmed the vulnerability was caught before any known exploitation and found no evidence of unauthorized value creation. User privacy was not compromised, and Sapling and transparent transactions continued operating normally throughout the incident.
Market impact
For ZEC holders and node operators, the key takeaway is that the response was fast and contained. The two-stage fork strategy — disable first, patch and re-enable second — reflects a mature incident-response playbook. Zebra node operators are strongly urged to upgrade to version 5.0.0 immediately. The clean resolution, with no exploitation confirmed, limits downside risk for ZEC and reinforces confidence in the Foundation's ability to handle protocol-level emergencies.
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