Aztec Discloses a Proving Flaw That Could Let Invalid Transactions Pass Verification

Aztec, the privacy-focused layer-2 network on Ethereum, has disclosed a critical vulnerability in the proving system of its Alpha V5 release. By the project's own description, an attacker could construct a proof that passes verification for a transaction the network is supposed to reject, and that transaction could then produce a state change outside the rules V5 is meant to enforce. Contributors say they cannot determine whether anyone exploited the flaw before they found it, and they are telling users to treat funds, applications and contract state on V5 as exposed until incident response finishes and operators complete the required network actions. The repair is planned for V6.

The category matters more than the individual bug. A smart-contract exploit abuses code that runs correctly. A soundness defect breaks the check that decides what counts as valid in the first place. On most rollups, validators re-execute transactions and can catch an invalid state root. On a network built to keep transaction contents private, that fallback is weaker by design, because the data needed to re-execute a transaction is the same data the system is built to hide.

Aztec says the finding came from internal auditing assisted by artificial-intelligence tooling, which creates a risk in both directions. The same capability that lets reviewers sweep proving code at scale is available to anyone looking for the next unsound constraint, and the first published result of that sweep was a critical flaw in a live network holding user funds.

The disclosure arrives while competitors make the same case to institutions. Miden has announced its PriFi stack for private digital finance and a self-custodial private wallet called Bread, built on client-side execution. Privacy networks are now selling confidentiality as a prerequisite for serious on-chain business, which means the proof system is not a technical detail for their buyers. It is the entire security argument.