Aztec says an AI audit found a proof-forgery flaw in its Alpha V5 network and it cannot tell whether anyone used it

Core contributors to Aztec, the Ethereum privacy layer-2 (L2) network, say they found a critical vulnerability in the proving system of the Alpha V5 network on 27 July 2026, using internal AI-assisted auditing. According to Aztec's disclosure, an attacker could build a proof that passes verification for a transaction the network should reject. If the network accepted it, that transaction could change state outside the rules V5 is meant to enforce.

The contributors say they cannot determine whether anyone exploited the flaw before they found it. The system does not record enough information to tell an ordinary transaction from one accepted through the faulty proving path, so past chain activity cannot show whether exploitation happened or how large it was. Aztec tells users to treat funds, applications and contract state on V5 as exposed to a protocol-level failure until incident response is complete. Contributors are working with operators, application teams and bridge operators while applications add security guards around the affected flows. The fix will ship in V6, which includes circuit updates that stop the network from accepting proofs tied to the affected proving system. Reviewers say they have found no other high or critical V5 issues so far.

The pattern repeats. Aztec disclosed a critical vulnerability in Alpha V4 earlier this year and told V4 users to withdraw before June 25, The Defiant reported. Aztec also says its AI audit harness has found critical bugs that months of human internal and external audits missed. Those fixes are part of the coming V6 release. At the same time, the team is planning further ahead and has published a post-quantum roadmap for the network.

The design is the reason this class of bug is so serious for Aztec. Private functions run on users' own devices, and the network sees only the proof that they ran correctly. No validator re-executes the private logic, so proof soundness is the only check. The usual rollup fallback of re-running transactions to catch errors does not exist for that part of the system.