MetaMask incident: on-chain analysis reveals the scale of the attack

The MetaMask incident has a number, and it's tiny. On the night of September 30, Metamask announced an infrastructure compromise and the preventive withdrawal of its validators from Lido, without saying what had leaked. Kaden's on-chain analysis, published on October 1, gives the outline of the attack: out of 19 validators who received a block reward, 18 paid for an address funded via Tornado Cash, for loot of around 0.36 ETH. Opposite, nearly 17,000 validators have already been released, or around 523,000 ETH. MetaMask has not confirmed these volumes.

Key Points

Around 17,000 MetaMask validators came out, worth almost 523,000 ETH, according to Kaden’s analysis

Out of 19 validators who received a block reward, 18 paid an unexpected address, for 0.36 ETH

Around 821 potentially affected validators remain active, including 3 suspected of having already been hijacked

Withdrawal keys are not in play. Residual risk is slashing if signing keys have leaked

What on-chain shows, what MetaMask doesn’t tell

The press release of the night of September 30 remained deliberately vague. MetaMask spoke of an incident on part of its infrastructure, of no immediate threat to wallets, and of a preventive exit of validators from its non-custodial staking activity. The detail arrives on October 1, not from the company, but from a researcher.

Internet user 0xKaden scrutinized the validators operated by MetaMask. Nineteen had cashed in a block reward. For 18 of them, the payment did not go to the intended fee recipient, but to the address 0x98B9…24A3, supplied from Tornado Cash. The amount captured is around 0.36 ETH. There is no indication, at this stage, that the attacker can withdraw the staked ETH. MetaMask also reminds that it does not hold its customers' withdrawal keys.

Disproportion is the real issue. Releasing 17,000 validators and more than half a million ETH for a loot of a few tenths of ether, showing that MetaMask does not yet know how far the access has reached. Kaden says he doesn't know if the attacker could modify all the fee recipients, or only those already observed.

What stays online

The release is not finished. Three validators suspected of having already seen their rewards diverted have not yet left the network. In total, approximately 821 potentially affected validators remain active, with no clear reason.

The sensitive point is not the theft of 0.36 ETH. If the attacker has obtained signature access, he can in theory force validators to behave in a slashable, double signature or contradictory attestation manner. Getting the machine out before it missigns is precisely what MetaMask is doing. The cost is downtime, and sometimes an inactivity penalty, not loss of principal.

Lido has already indicated that the last validators affected should be released, without being withdrawn yet, by October 7. ETH is not going back to work right away. Between exit, withdrawal and new entry, the cycle can take up to around 45 days, due to the entry queue. stETH holders do not need to do anything. The protocol will lose rewards over this period.

MetaMask has still not said which system was compromised, or how. Until this post-mortem exists, the 523,000 ETH released remains a researcher's estimate, not a company figure.