An attacker drained zkLink Nova's Ethereum escrow down to approximately 0.001 ETH on Wednesday, October 28, using a public relayer to submit a forged batch root to the network. Blockchain security firm Blockaid, which flagged the exploit, estimates that roughly $786,000 in ETH and ERC-20 tokens has been taken so far and warned that the attack was still ongoing at the time of its report.

Blockaid flagged the public relayer attack at 10:24 p.m. ET

Blockaid disclosed the incident in a post on X at 10:24 p.m. ET on October 28. According to the firm, the attacker used a public relayer to inject a fake root on Ethereum and then finalized ETH and ERC-20 withdrawals from Nova's Layer 1 escrow to recipient addresses of their choosing.

"~$786k drained from L1 ETH escrow and ERC20 bridge so far. Attack still ongoing," Blockaid wrote.

zkLink Nova takes in assets from Ethereum and its connected Layer 2 networks and pools them. Deposits remain in contracts on their source chains and are credited to Nova through its canonical bridge. A batch root is the hash value a bridge uses to verify messages; in this case, the withdrawals Nova approved. Under zkLink's settlement design, batches must clear proof checks and cross-chain consistency checks before they can be finalized, and withdrawals may proceed only after the batch root is committed to connected chains. That architecture places assets pooled from multiple chains behind a single verification step, meaning one incorrectly validated root can authorize withdrawals against the entire escrow balance rather than an individual account.

Blockaid said the forged root was instead injected on Ethereum through a public relayer. Transaction logs for the attack show a new batch root logged in the same transaction as the ETH and token withdrawals, immediately before them.

Single 6:21 p.m. transaction moved $778,625.84 to one recipient

The largest transaction took place on October 28 at 6:21 p.m. ET, a few hours before Blockaid's alert. It removed 22.43 ETH from Nova's Ethereum escrow along with 11 ERC-20 tokens from the token bridge and sent everything to a single address. Blockaid's thread named two addresses used by the hacker and identified the ERC-20 bridge as a second target contract.

The largest lot was 245.74 pufETH, worth around $613,536 at Etherscan prices. About 18,113 USDC and 3,361 USDT went out with it. At the prices displayed by Etherscan, the transfers total $778,625.84, though because the figure covers only one transaction, total losses are difficult to establish.

Etherscan later showed that only about 0.001 ETH remained in the hacked ETH escrow. As of 10:29 p.m. ET, however, the escrow's pause flag had still not been set, leaving it unclear whether other controls had halted any further withdrawals. The open items at the time of writing were whether the pause flag would be set and what the final loss total would reach once all affected transactions were counted.

Forged inputs hit another bridge 11 days earlier

The zkLink incident was the second in 11 days to involve falsified bridge inputs. On October 17, as Cryptopolitan reported, a fake mint message was used to create 10 million unauthorized CYS tokens through Cysic's cross-chain bridge. The Cysic attacker sold 7.2 million of the tokens, and their wallet sent about $727,000 to Ethereum before the project blacklisted it.

Separately, around $7.54 million left the Verus Ethereum bridge in July, the second time the bridge had lost funds. In May, $11.58 million was taken in the first incident. Blockaid linked the two Verus attacks to the same contract and import route. The May exploit stemmed from roughly 10 lines of missing Solidity validation in the bridge's checkCCEValues function, the same class of validation error behind the 2022 Wormhole and Nomad attacks — breaches that drained hundreds of millions of dollars combined that year. The recent cluster of incidents built on fake mint messages, forged batch roots, and missing validation checks illustrates how much pooled cross-chain value can hinge on a bridge's verification code.