Aztec's decommissioned legacy infrastructure suffered two attacks within three days, resulting in losses exceeding $4 million. The affected system was a contract system retired several years ago, not the current Aztec network itself. Aztec stated that the existing network's smart contracts and AZTEC ERC20 tokens were unaffected.
The initial attack resulted in approximately $2.1 million in losses.
The first incident occurred on June 14th, targeting the decommissioned privacy bridging protocol Aztec Connect. Although the product had long been discontinued, some funds remained in the on-chain contract.
The attackers transferred approximately $2.1 million in assets, including about 909 ETH, 270,000 DAI, and 167 wstETH, along with a small amount of other tokens. The problem lay in the rollup proof verification process. The attackers exploited a flaw in the verification logic, allowing invalid or tampered proofs to pass the check, thus triggering unauthorized withdrawals.
Aztec Connect contracts were designed to be immutable upon deployment. This means that once a contract is live, it cannot be paused or patched. Although users were previously advised to withdraw their funds before the product shut down, residual liquidity ultimately became a target for attacks.
The second attack resulted in further losses of approximately $2.15 million.
Three days later, another older system, Private Rollup Bridge, was used again. This contract also belonged to Aztec's early infrastructure and had been abandoned after the old rollup architecture was phased out.
This time, the attacker transferred approximately 1,158 ETH, worth nearly $2.15 million at the time of the incident. While the execution method differed from the previous attack, the underlying technology was similar. The attacker exploited the "escape route" mechanism in the bridging design, submitting a specially crafted zero-knowledge proof to erroneously trigger the contract exit process, subsequently withdrawing all liquidity in one go.
The report points out that neither of these incidents involved private key leaks nor common reentrancy attacks. The problem lies more in the flawed connection between zero-knowledge proof verification and on-chain settlement in older versions of the rollup system.
Aztec stated that the current network is unaffected.
Following the two incidents, Aztec Labs and the Aztec Foundation stated that the affected products had been discontinued several years ago and were unrelated to the current Aztec network and AZTEC token ecosystem. Neither of the old contracts could be upgraded, suspended, or taken over by the team because they were configured to be immutable at deployment.
Security firm CertiK also issued a warning about the Private Rollup Bridge incident and flagged the attacker's address and related Ethereum transactions. Multiple analyses generally agree that the vulnerability stemmed primarily from the zero-knowledge proof verification design, rather than from errors in traditional smart contract coding.
Although the two attacks occurred close together and both involved proof-verification flaws, Aztec claims they are independent events. This series of thefts also highlights that retired DeFi contracts that still retain on-chain funds can potentially become entry points for attacks years later.
