What happened
Nomad's Ethereum bridge was exploited on August 1, 2022 after a Replica contract upgrade made an unproven message appear valid. Attackers and copycats submitted forged messages directly to the bridge, releasing escrowed assets without corresponding source-chain transfers. Later reporting commonly rounded the incident to $190 million; it involved more than 300 participating addresses.
The message-authentication path treated a default mapping value as an acceptable committed Merkle root. A compatibility-oriented initialization state combined with the process() upgrade to authorize messages that were never proven. Authentication code must distinguish an uninitialized or default value from a confirmed state, and upgrades must test all default-state transitions.
Case & protocol details
Attack Timeline
Replica initialization had set confirmAt[bytes32(0)] to 1 for an empty Merkle-tree root. After the upgraded process() logic called acceptableRoot(messages[messageHash]), an unproven forged message read the default root bytes32(0). That root now appeared acceptable because its timestamp was 1, so the authentication check passed.
Attackers could submit fake messages directly to the Ethereum Replica, which forwarded them to BridgeRouter and released escrowed assets without a matching deposit or burn. Once the calldata was public, copycats changed only the recipient address and repeated the withdrawal pattern.
Security review history
- Quantstamp No public report
Funds Recovery
Recovered
$36.3M
Net Loss
$153,710,000
Evidence & learning
Attack pattern
Compare incidents →Sources and on-chain records
- report Report twitter.com
- report Post-mortem medium.com
- transaction Transaction etherscan.io
- code Code reference github.com
- analysis Website reference cointelegraph.com
- analysis Website reference coindesk.com
- analysis Website reference livemint.com
- analysis Coinbase Nomad bridge incident analysis coinbase.com
- analysis Mandiant analysis of the Nomad bridge exploit cloud.google.com
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