Zcash patches Orchard bug; emergency Zebra updates restore pool

The Zcash Foundation released emergency Zebra 4.5.3 and 5.0.0 on June 3 to address a critical flaw in the Orchard Action circuit, the zero-knowledge system that validates Orchard shielded transactions. Zebra 4.5.3 paused Orchard actions at block height 3,363,426 using an emergency soft fork. Zebra 5.0.0 activated NU6.2 at block 3,364,600 and restored Orchard after the circuit was corrected.

The Foundation reported the flaw could have allowed value to be created without detection if exploited, and it stated there was no known exploitation. The organization confirmed the total ZEC supply remained unchanged during the incident.

Transparent and Sapling transactions continued to process while Orchard was paused. On X the Foundation posted: “Zebra 5.0.0 is out – all node operators should upgrade now. NU6.2 activated, re-enabling Orchard with a corrected circuit. Total ZEC supply confirmed intact throughout.” The team urged all node operators to upgrade to Zebra 5.0.0 immediately.

Some users and explorers showed the chain near height 3,364,601 for several hours during the upgrade window, prompting reports that block production had stopped. Mining pools continued to produce blocks under the updated consensus rules while explorers and other infrastructure resynced. By midday on June 3 most services had caught up to the upgraded network.

ZEC traded around $596 at the time of reporting, up more than 5% over 24 hours and moving between about $560 and $638 during the day. Market capitalization was near $9.9 billion, placing ZEC around 13th by capitalization. Some market participants have discussed potential institutional products for ZEC, but no approvals or launches are confirmed.

Both emergency releases were deployed within days of discovery, and the Foundation said the response prevented any detected loss of funds. Security and upgrade work will continue as node operators complete the upgrade to Zebra 5.0.0.