An attacker and hundreds of copypasta looters withdrew over $190 million from Nomad bridge. Here’s a simple explanation of what happened.

What is the Nomad bridge?

Nomad is a cross-chain bridge for sending tokens between Ethereum, Avalanche, Evmos, Milkomeda C1, and Moonbeam networks.

How did Nomad get hacked?

It appears that the attacker first managed to withdraw 100 WBTC, which they then immediately swapped for WETH and ETH.

Nomad bridge attacker
The first transaction from the Nomad bridge hacker

The attacker dumped all the tokens and converted all to ETH. The hacker's wallet still holds >2k ETH.

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UPD: On August 6, the hacker returned 1,885 ETH (~$3.2 million) to the bridge address.
Nomad bridge hacker's wallet
The Nomad hacker's wallet

Over the next couple of hours, Nomad’s wallet balance went down from >$190 million to $16.5k.

Nomad bridge's address
Nomad bridge's address

The original cause of the attack was that Nomad's smart contract failed to properly validate the input of the transaction.

What’s unique about this attack is that thousands of addresses looted Nomad’s account.

It appears that they were able to copy & paste the attacker’s original call data, adding their own addresses. If you want to understand how this was possible, 0xfoobar has done a post-mortem on the attack.

Nomad also published their detailed own root cause analysis of the attack.

In short: the attacker found a vulnerability in the smart code. It doesn’t look like this could affect other bridges.

Over $36 million returned by white hat hackers

Luckily, some of the ‘looting’ addresses have said they acted as 'white hat hackers' and returned the funds:

So far, more than 40 addresses returned over $36 million to the Nomad recovery address.

Could it be because people were after the highly sought-after RAAVE tickets?

Nomad also announced an up to 10% bounty: those who return >90% of funds they looted will be considered white hat and can keep the rest. Nomad will not pursue any legal action against those who returned funds.

What can you do?

If you had funds bridged via Nomad, unfortunately, there likely's nothing you can do.

Please ignore any impersonators who promise to “return funds” — those are scammers.

The best thing to do now is to wait until official instructions from the Nomad team and the affected networks' teams.

You can also poke around the transaction history for Nomad’s smart contract address and see who was withdrawn assets.

A telltale of the attacker or copycat looter (some even used their ENS handles) are transactions with the same amounts — it’s all on-chain.

Suspicious transactions during Nomad bridge attack
Suspicious transactions during Nomad bridge attack

If you see a suspicious transaction, tweet them with a link.

Maybe as a community, we could call on more people to declare their actions as “white hat” and return the funds.