Zcash sell-off deepens after hidden flaw

Zcash tumbled by more than 30 per cent after the public disclosure of a critical flaw in its Orchard shielded pool raised fresh questions over confidence in one of the crypto market’s best-known privacy coins.

The fall followed the revelation that a vulnerability left undetected for nearly four years could, in theory, have allowed an attacker to create unlimited counterfeit ZEC inside Orchard without immediate detection. The bug has been fixed through an emergency network upgrade, and no exploit has been confirmed, but the disclosure hit a token already vulnerable after a sharp rally.

ZEC traded near $390 to $450 during Friday’s volatile session, with market data showing a 24-hour fall of roughly one-third and trading volumes above $1.6bn. The token’s circulating supply stands at about 16.7 million coins against a maximum supply of 21 million, making any credible question over undetected inflation especially sensitive for investors.

The flaw centred on Orchard, Zcash’s newest shielded pool, launched with the NU5 upgrade in May 2022. Orchard was designed to strengthen private transactions using the Halo proving system, remove reliance on a trusted setup and support unified addresses that route funds into the most private available pool. Its role at the centre of Zcash’s privacy architecture meant the vulnerability carried significance beyond a routine software defect.

Security researcher Taylor Hornby discovered the issue on May 29 and privately disclosed it to Zcash developers. Engineers then moved through a rapid containment process, first disabling Orchard actions through a temporary soft fork on June 2 before activating the NU6.2 hard fork on June 3. The hard fork restored Orchard with a corrected circuit and closed the flaw.

The vulnerability has been described as a soundness bug in the zero-knowledge proof circuit that validates private transactions. Such a defect can cause a blockchain to accept a transaction that should have failed. In this case, the weakness reportedly involved an under-constrained part of the Orchard circuit, allowing false inputs to pass through a cryptographic check.

The central concern is not that counterfeit coins have been proven to exist, but that Orchard’s privacy design prevents a simple public audit capable of ruling out exploitation with absolute certainty. That uncertainty is precisely what unsettled traders, because Zcash’s value proposition rests on both privacy and confidence in the fixed supply.

Developers and affiliated ecosystem groups have stressed that users’ funds were not reported lost and transaction privacy was not compromised by the patching process. The emergency response also demonstrated coordination between engineers, miners and service providers. Even so, the episode has exposed the tension at the heart of privacy-preserving cryptocurrencies: the same features that shield legitimate users can make certain forms of retrospective verification more difficult.

The sell-off also reflected broader pressure on digital assets, where privacy coins often face sharper swings because of thinner liquidity, regulatory scrutiny and concentrated investor interest. Zcash had drawn renewed attention before the disclosure as shielded usage increased and market participants debated whether privacy tokens could regain relevance amid surveillance concerns in digital finance.

Orchard’s shielded pool had become a growing part of the network. More than 30 per cent of circulating ZEC is now held in shielded pools, with Orchard accounting for much of the expansion since its launch. That growth amplified the market reaction, as investors reassessed the implications of a long-lived defect in the protocol’s most advanced privacy layer.

The episode also drew attention because an artificial intelligence-assisted process was involved in developing a working proof-of-concept exploit in a local test environment. That detail has sharpened debate across the crypto security sector over whether advanced AI tools are lowering the barrier for discovering both defensive vulnerabilities and offensive attack paths.

Zcash has faced this type of confidence test before. A separate counterfeiting vulnerability disclosed in 2019 also involved the risk of undetectable inflation in shielded transactions and was patched without confirmed exploitation. The recurrence of a similar fear, even in a different technical component, has revived scrutiny of how privacy networks prove monetary integrity while preserving confidentiality.