Scenarios without proper validation

Scenarios of vulnerabilities targeting relayers (filler) in hybrid cross-chain and account abstraction systems. These attacks exploit the dual role relayers play as both liquidity providers and transaction bundlers, causing financial harm through uncompensated gas consumption.

1. Unfunded Account Exploitation

Root Cause

This vulnerability occurs when relayers fail to implement adequate fund verification before executing UserOperations. Unlike standalone ERC-4337 bundlers that perform comprehensive pre-execution validation, hybrid relayers often prioritize cross-chain profitability calculations while neglecting account abstraction validation requirements. The EntryPoint contract performs fund verification during execution, but by that point, the relayer has already committed gas costs that become unrecoverable when transactions revert.

Attack Flow

1. Attacker creates a UserOperation with an unfunded smart account (zero balance, no paymaster)

2. Relayer performs basic profitability assessment for the cross-chain component without validating account funds

3. Relayer submits the operation to EntryPoint.handleOps()

4. Transaction reverts during prepayment validation when EntryPoint attempts to charge gas fees

5. Relayer loses gas costs without receiving compensation from the failed operation

Mitigation

Implement comprehensive fund verification as part of the hybrid profitability assessment:

Economic Validation = Cross-Chain Profitability + UserOperation Fund Verification

Required Prefund = Sum of (Gas Limit × Max Fee Per Gas) for:
  - Call Gas Limit  
  - Verification Gas Limit
  - Pre-verification Gas

Account Funded = balanceOf(userOp.sender) >= Required Prefund OR 
                paymasterDeposit >= Required Prefund

Accept Operation = Economic Validation AND Account Funded

Entity reputation tracking per ERC-7562 should also be implemented:

Inclusion Rate = (Operations Included × 1e18) ÷ Operations Seen
Throttled = Max Seen > Operations Included + THROTTLING_SLACK

2. Simulation-Execution Mismatch

Root Cause

This vulnerability exploits the temporal gap between relayer simulation and on-chain execution. Smart contracts can implement conditional logic using environment-dependent opcodes (block.timestamp, block.number, block.difficulty) that execute differently at simulation time versus execution time. Relayer performing profitability analysis during simulation may significantly underestimate actual gas consumption, leading to unprofitable operations.

Attack Flow

1. Attacker deploys a contract with conditional logic based on block.timestamp or similar environment variables

2. Contract executes normally during simulation but consumes excessive gas when specific conditions are met

3. Attacker creates cross-chain intent targeting the malicious contract as recipient

4. During relayer simulation, contract appears to consume normal gas amounts

5. At actual execution time, environmental conditions trigger high gas consumption

6. Relayer suffers unexpected gas costs that exceed fee revenue

Example code:

contract MaliciousRecipient {
    function executeOrder() external payable {
        if (block.timestamp % 100 == 0) {
            // Expensive operation triggered by timestamp condition
            for (uint i = 0; i < 10000; i++) {
                keccak256(abi.encode(i, block.timestamp));
            }
        }
    }
}

Mitigation

Implement ERC-7562 opcode restrictions and enhanced gas estimation with safety margins:

Opcode Validation: Restrict access to environment-dependent opcodes during UserOperation validation:

• Block ORIGIN, GASPRICE, BLOCKHASH, COINBASE, TIMESTAMP, NUMBER, PREVRANDAO, GASLIMIT, BASEFEE

• Implement storage access sandboxing via SLOAD/SSTORE restrictions

Enhanced Gas Estimation:

Estimated Gas Cost = Base Gas Estimate × Gas Multiplier × Gas Padding
Total Gas Cost USD = (Estimated Gas Cost + Cross-Chain Message Cost) × Gas Token Price
Safety Margin = Gas Cost USD × SAFETY_MULTIPLIER

Profitable = Total Revenue >= Total Gas Cost USD + Safety Margin + Minimum Profit

Simulation-Based Validation:

// Pre-execution validation
(bool success, bytes memory returnData) = entryPoint.simulateValidation(userOp);
require(success && !detectsForbiddenOpcodes(returnData));
require(gasUsed <= userOp.verificationGasLimit + VALIDATION_GAS_SLACK);

Implement circuit breakers that halt operations when validation failure rates exceed configured thresholds, protecting against systematic exploitation attempts.