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Morning Edition · Monday, October 5, 2026Published at 1:31 AM EDT · New York
Aztec reopens private payments with transfer caps while a proving-system flaw in Alpha V5 stays unfixed
Contributors say a forged proof could pass verification for an invalid transaction, and they cannot tell from chain history whether anyone has already used the flaw.
Aztec, the privacy-focused Ethereum layer-2 network, is running its Alpha V5 release with a critical defect in its proving system. In its disclosure, Aztec says core contributors found the flaw on July 27 through internal AI-assisted auditing. An attacker may be able to construct a proof that passes verification for a transaction the network should reject. If the network accepted that proof, the transaction could change state outside the rules V5 is meant to enforce. Unchained reported that the flaw was disclosed on August 7.
Contributors say they cannot determine whether anyone exploited the flaw before they found it. The Alpha V5 system does not record enough information to separate ordinary transactions from transactions accepted through the flawed proving path, so chain history cannot settle the question. Aztec told teams planning V5 deployments to pause. It told teams with live contracts to limit user exposure, isolate affected functions and be ready to move users to new deployments. The fix will arrive with V6, which will update the circuits (the arithmetic programs that define what a valid proof must show) so the network rejects proofs tied to the affected system. Aztec says human audits found no other high-severity issues in V5.
Aztec Labs nevertheless relaunched zk.money, its private payments wallet, on September 29, before V6 ships. Each deposit, payment and withdrawal is capped below $2,500, and a $50,000 daily deposit limit applies across all users, Incrypted reported. Aztec Labs attributes the caps to new, experimental cryptography. The caps also limit how much an attacker could take through a forged proof.
What this means
The exposure is structural. Most rollup security models assume that someone can detect an invalid state transition. A soundness bug in the prover defeats that assumption, because the invalid transaction looks valid to every verifier. Aztec's statement that it cannot tell whether the flaw was exploited is a plain admission that this class of failure cannot be audited after the fact. Users of zk.money carry the risk, and so do builders who deployed on V5. Holders of privacy-layer-2 tokens are exposed indirectly, because investors will discount any network whose correctness cannot be checked. The cap is a reasonable control because it limits how much one exploit can extract. The market still underrates the argument that privacy networks need several independent proof systems and a user withdrawal path that works even if the network stalls before deposits should grow. The desk's read is that Aztec keeps the caps until V6 ships and that other zero-knowledge rollups add similar per-transaction limits or second provers within months. A V6 release that lifts the caps without an independent proof-system review would show the read is wrong.
Part of a tracked trend
Proving-System Bugs Become a Distinct Rollup Risk
Soundness defects in zero-knowledge proving systems will keep surfacing as a risk class separate from smart-contract exploits, because validator re-execution — the fallback most rollups rely on — cannot catch them, forcing teams into embargoed disclosure timed to upgrades and pushing users toward proof-system diversity and escape hatches.
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Comments
1Oct 5, 5:31 AM · edited
Caps on each transfer bound the size of any single forged payment but not cumulative loss, since an attacker could split value across many transfers unless an aggregate limit also applies.