Aztec Connect Drained of $2.1M Through Deprecated Contract Three Years After Shutdown

An attacker drained roughly $2.1 million from a deprecated Aztec Connect smart contract on Sunday, three years after the privacy bridge was shut down, by abusing a flaw in how the contract verified zero-knowledge proofs.

The exploit hit the RollupProcessorV3 contract at around 8:26 a.m. ET Sunday, Aztec Labs said in a statement confirming the incident. The attacker pulled out 908.99 ETH worth about $1.6 million at current prices, 270,513 DAI, and 167.89 wrapped staked ETH worth roughly $357,000, along with smaller amounts of yvDAI, yvWETH, LUSD, and yvLUSD, according to BlockSec's analysis. The funds left through a single entry-point transaction on Ethereum.

Aztec Labs said it can do nothing about it. Aztec Connect was deprecated three years ago, and the team holds no admin keys over the system. It cannot pause or upgrade the contracts, and it cannot reverse the transactions.

The Proof-Verification Mismatch

The vulnerability sat in the contract's `processRollup()` function, where the zero-knowledge proof verification path and the Ethereum settlement logic handled the same transaction batch differently, per the technical breakdown. Zero-knowledge proofs are cryptographic shortcuts that let one party prove a statement is true without revealing the underlying data.

The proof-verification path decoded every transaction in a batch and inserted it into the rollup's record. The Layer 1 settlement path only processed a subset, set by a parameter called `numRealTxs`. The attacker crafted a rollup that placed legitimate-looking deposit slots late in the batch while keeping `numRealTxs` artificially low, the analysis found. That let the contract credit balances that were never backed by real deposits, then withdraw them.

The attacker used 14 batched rollup IDs to extract the funds, according to the same analysis. The originating wallet, 0x0f18…edd17, had been funded through Tornado Cash, the Ethereum mixer, which attackers can use to obscure where their capital came from.

BlockSec noted that the RollupProcessorV3 contract was upgraded in April 2024, after Aztec Connect had already entered its sunset, and that the upgrade was not put through an external security audit before deployment.

A Bridge No One Was Watching

Aztec Connect launched in July 2022 as a privacy-focused zk-rollup bridge that let users run DeFi transactions on Ethereum without exposing the details on-chain. Aztec Labs stopped accepting new deposits in March 2023 and wound down the off-chain infrastructure that ran the rollup, leaving the on-chain contracts live but unattended.

The architecture built to make Aztec Connect trustless and censorship-resistant is the same architecture that now blocks any cleanup. Because the contracts are immutable and no party controls them, the drained funds cannot be clawed back through the protocol.

CertiK flagged the suspicious transaction to its followers shortly after it landed. The Aztec Foundation said the exploited product has no connection to the AZTEC ERC-20 token or the current Aztec network, and that the live chain and its users were unaffected.

Zombie-Contracts

The drain extends a run of attacks on abandoned-but-funded contracts that keep sitting on-chain long after their operators move on. Raydium confirmed a $1.34 million drain of its deprecated AMM V3 pools on Solana last week, with the attacker bridging proceeds to Ethereum through Tornado Cash. Days earlier, old DxSale token lockers were drained for $7.3 million across roughly 1,400 BNB Chain pools.

Aztec Labs said it had repeatedly urged users to withdraw their funds from the legacy system before the shutdown.

The current Aztec network, a separate privacy Layer 2, continues to run on its own contracts.