QA-08: Txpool Admission Ignores Value and max_fee_per_gas

monad-qa-08-txpool-admission-ignores-solvency

Summary

The txpool admission path compares sender balance only against last_commit_base_fee * gas_limit and does not account for transaction value or max_fee_per_gas.

Vulnerability details

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let last_commit_base_fee = last_commit.execution_inputs.base_fee_per_gas;
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for tx in txs {
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    if account_balances
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        .get(tx.signer_ref())
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        .is_none_or(|account_balance_state| {
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            account_balance_state.balance
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                < last_commit_base_fee.saturating_mul(tx.gas_limit())
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        })
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    {
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        event_tracker.drop(tx.hash(), EthTxPoolDropReason::InsufficientBalance);
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        continue;
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    }

Impact

The pool can admit transactions that are insolvent under the normal Ethereum-style upfront cost check, causing mempool pollution and proposer inefficiency.

Recommendation

Align admission checks with full upfront solvency requirements.