ETH reentrancy through uncapped calls

Severity: High ID: reentrancy-eth

Flags uncapped ETH-transferring low-level call operations when state read before the call is written after the call.

What it does

Warns when a function performs .call{value: ...}(...) without a concrete gas cap, or with gas: gasleft(), and later writes a state variable that was read before the call on the same reachable path. Local internal helper calls and modifiers are analyzed when their bodies are available. This uses Slither's reentrancy-eth detector name, while intentionally narrowing reporting to uncapped ETH-transferring low-level calls.

Why is this bad?

Unlike transfer and send, low-level call forwards all remaining gas by default. A malicious recipient can run complex fallback logic and re-enter the caller before later state changes occur. If the function uses stale state read before the call and updates that state only afterward, the recipient may be able to repeat or reorder effects.

This lint is intentionally conservative to avoid noisy findings: it does not report event-only ordering issues, unrelated state writes, zero-value calls, constructor-time calls, or calls with an explicit gas cap.

Example

Bad

function withdraw() external {
    uint256 amount = balances[msg.sender];
    (bool ok, ) = payable(msg.sender).call{value: amount}("");
    require(ok, "transfer failed");
    balances[msg.sender] = 0;
}

Good

function withdraw() external {
    uint256 amount = balances[msg.sender];
    balances[msg.sender] = 0;
    (bool ok, ) = payable(msg.sender).call{value: amount}("");
    require(ok, "transfer failed");
}