Zcash: Completed the NU 6.2 hard fork and fixed the Orchard pool vulnerability

The official announcement from the Zcash (ZEC) Foundation states that independent security researcher Taylor Hornby discovered a serious reliability vulnerability in the Orchard zero-knowledge proof circuit on May 29, which could allow double spending within the Orchard pool.

Core engineers from ZODL confirmed the issue within hours and initiated a fix. To buy time, they temporarily disabled Orchard operations through an emergency soft fork of Zebra 4.5.3 in the early hours of June 2. Finally, today, they activated the NU6.2 hard fork through Zebra 5.0 — at 12:05 PM Beijing time, the mainnet successfully completed the upgrade at block height 3,364,600, re-enabling Orchard with the corrected circuit, and the vulnerability was permanently closed.

This is the second time Zcash has triggered a protocol upgrade due to security issues since its launch in 2016, with no known exploits occurring during the process. The network's total supply guard mechanism confirmed that the total supply remained intact, and user privacy, as well as Sapling and transparent transactions, were not affected.