On June 22, the Ethereum Layer 2 network Taiko announced via X that the security incident involving its cross-chain bridge had been contained. Preliminary estimates place the total loss at approximately $1.7 million, with affected contracts now under emergency suspension.
Attack Vector: Forged Message Proofs
The attacker exploited a vulnerability in Taiko's message proof verification mechanism. Without any legitimate transaction on the source chain, Ethereum mainnet accepted forged message credentials. The attacker then initiated fake withdrawals, draining assets from the bridge and token vaults. Security firm Blockaid's early analysis traced the issue to a flaw in how Taiko's bridge validates source-signal proofs. The attacker was able to submit message proofs lacking valid Taiko chain evidence, registering and extracting fraudulent bridge messages, leading to unauthorized release of ERC20 vault assets.
Risk Containment: L1 Bridge and Vault Paused
Taiko confirmed the following actions: L1 bridge paused, disabling all withdrawals via that channel; ERC20 vault stopped, cutting off asset outflow; and new block production halted (already in effect earlier that day) to stabilize the on-chain state.
Event Timeline (UTC+8)
- 08:04 Blockaid detected the attack on Taiko's ERC20 vault, with losses exceeding $1 million.
- 09:48 PeckShield tracked the attacker moving 1.99 million TAIKO tokens to MEXC, worth around $189,000.
- 11:31 Taiko suspended all proposers from generating new blocks.
- 13:55 Taiko announced the chain state verification mechanism had been compromised, rendering bridge security assumptions unreliable.
- 14:14 Taiko declared risk contained; L1 bridge and ERC20 vault paused.
A Lesson for Type-1 zkEVM
Taiko markets itself as a “Type-1 zkEVM,” meaning its L2 state is built directly atop Ethereum mainnet rather than a separate rollup chain—theoretically carrying Ethereum-grade security. Yet this incident underscores that the message validation logic of the cross-layer bridge is the real security bottleneck, not the final state machine. Even if the state machine is airtight, forged proofs can still infiltrate mainnet. The event mirrors a common pattern in the L2 landscape: “eventual consistency” depends heavily on the correctness of intermediate steps (message proofs, source-signal verification), not the finality algorithm itself. Taiko halted block production in the morning and confirmed risk control by afternoon—a response time within normal range for L2 projects.