Hornby disclosed the flaw to Zcash Open Development Lab (ZODL) engineers that same evening. Within hours, a team of protocol developers confirmed the issue and began a carefully orchestrated, confidential response designed to prevent exploitation before a fix could be deployed.
The coordinated repair unfolded over five days. Developers first issued an emergency soft fork—essentially a temporary rule change—that shut down Orchard transactions entirely while the patch was being finalized. Private coordination with miners and exchanges began the evening of May 31. An initial activation attempt ran into deployment snags, but a second attempt succeeded early Monday morning, halting all Orchard activity at block 3,363,426.
The permanent fix arrived Wednesday, when a full network upgrade—dubbed NU6.2—restored Orchard functionality using a corrected circuit. Such a hard fork was necessary because repairing a zero-knowledge proof system requires updating a cryptographic verifying key, a change that cannot be made through ordinary software patches.
Officials said the total supply of ZEC was never at risk. Zcash's built-in "turnstile" mechanism, which tracks value across all transaction pools, confirmed no unauthorized coins were created. There is no evidence the bug was ever exploited.
The Foundation urged all node operators to upgrade immediately to Zebra 5.0.0, the software release that activates the corrected network rules.
Following the upgrade, block explorers appeared to show that the network hadn’t produced blocks in hours, fueling speculation of downtime. However, experts and the block explorers themselves have said that the network was running as normal, but that explorers were temporarily impacted as they upgraded their own network nodes.
The price of Zcash (ZEC) doesn’t appear to have been impacted at all by the disclosure of the emergency upgrade, with the privacy-centric coin continuing its latest upward swing. ZEC is currently up more than 10% over the last 24 hours at a recent price near $629, pushing its 30-day rise above 53%.
ZEC is now up 1,084% over the last year, pumping last fall to a recent high of nearly $700—a price that it has come close to matching in recent weeks. Even so, ZEC remains well off its all-time peak of $3,191 set in 2016.
