# Aztec Says a Proving-System Flaw Lets an Invalid Transaction Pass Verification on Alpha V5

Contributors found the defect through internal artificial-intelligence-assisted auditing and say the repair arrives only with the next network version, leaving current funds and applications exposed in the meantime.

- Published: 2026-09-20T05:45:09.559Z
- Canonical: https://polylog.news/crypto/2026-09-20/aztec-says-a-proving-system-flaw-lets-an-invalid-transaction
- Publisher: Polylog (Crypto desk)
- Section: crypto
- Sources: [Aztec Network](https://aztec.network/blog/alpha-v5-proving-system-vulnerability), [Aztec Network (Alpha V5)](https://aztec.network/alpha-v5), [Aztec Network (applications)](https://aztec.network/blog/dark-forest-aztec-game-goes-live)

Aztec, the privacy-focused Ethereum layer-2 network, [disclosed a critical vulnerability](https://aztec.network/blog/alpha-v5-proving-system-vulnerability) in the proving system that secures its Alpha V5 release. By the project's own description, an attacker may be able to construct a proof that passes verification for a transaction the network is supposed to reject. If the network accepts that proof, the chain can move into a state its rules forbid.

That is a different class of failure from a smart-contract bug. In a zero-knowledge system, the proof is the only thing a verifier checks, so a soundness defect turns the verification step itself into the weak point. Re-execution by validators, the fallback most rollups rely on, cannot detect it, because the invalid transition is accepted as valid by construction.

Aztec says core contributors identified the flaw through internal auditing assisted by artificial-intelligence tooling, after internal and external human audits had already completed without finding it. The project says reviewers have identified no other high-severity or critical issues in V5 at this time, and that the fix ships in V6, planned for later in 2026. Until incident response and operator action finish, Aztec advises users to treat funds, applications and contract state on [V5](https://aztec.network/alpha-v5) as exposed to a protocol-level failure. Applications are already [live on the network](https://aztec.network/blog/dark-forest-aztec-game-goes-live).

The disclosure challenges the central promise of shielded systems directly. A privacy chain asks users to trust mathematics instead of an operator, and a proving bug converts that trust into the possibility of unauthorized state changes inside a set where balances are hidden by design.

## What this means

Privacy networks concentrate risk in one component that almost no user can audit, and Aztec's notice shows the review process protocols currently rely on did not catch it until artificial-intelligence-assisted tooling was pointed at the circuits. Holders of assets on any single-proof-system rollup are exposed through the same channel: if the verifier accepts a bad proof, the shielded supply cannot be reconciled by inspection. Teams building on early privacy layer-2 networks lose development time and user deposits during remediation, and competing projects that offer escape hatches or multiple proof systems gain an argument.

## What to watch

- Whether Aztec publishes a technical post-mortem naming the specific circuit or verifier defect, which would tell other proving teams whether the bug pattern is shared across systems built on similar arithmetization.
- Whether operators of Alpha V5 halt or restrict the network before V6 ships, since a long exposure window with live applications is a different risk than an immediate pause.
- Whether other zero-knowledge rollups run the same artificial-intelligence-assisted review on their own proving stacks and disclose results, which would show if this is one team's defect or a category-wide backlog.