Added challenge 5

contracts/N5-BecomeMaster-medium.sol

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+// Props to band0x for this amazing CTF
+// I think we could upload this one as is, unless someone thinks otherwise
+// SPDX-License-Identifier: UNLICENSED
+pragma solidity 0.8.11;
+
+contract N5BecomeMaster {
+    mapping(address => uint256) allocations;
+    address public admin;
+    address public master;
+    address caller;
+
+    constructor() payable {
+        master = msg.sender;
+    }
+
+    modifier onlyMaster() {
+        require(master == tx.origin, "caller is not the master");
+        _;
+    }
+    modifier onlyContract() {
+        require(msg.sender != tx.origin, "caller is not the master");
+        _;
+    }
+    modifier onlyAdmin() {
+        require(admin == tx.origin, "caller is not the Admin");
+        _;
+    }
+
+    function allocate() public payable {
+        allocations[caller] = allocations[caller] += (msg.value);
+        admin = tx.origin;
+    }
+
+    function sendAllocation(address payable allocator) public {
+        require(allocations[allocator] > 0);
+        allocator.transfer(allocations[allocator]);
+    }
+
+    function takeMasterRole() public onlyAdmin onlyContract {
+        master = admin;
+    }
+
+    function collectAllocations() public onlyMaster onlyContract {
+        payable(msg.sender).transfer(address(this).balance);
+    }
+
+    function allocatorBalance(address allocator) public view returns (uint256) {
+        return allocations[allocator];
+    }
+}

contracts/hacks/N5-BecomeMasterhack.sol

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+// SPDX-License-Identifier: UNLICENSED
+pragma solidity 0.8.11;
+
+import "../N5-BecomeMaster-medium.sol";
+
+contract N5ExploitHack {
+    constructor(N5BecomeMaster instance) payable {
+    // Complete with your own code
+    }
+
+    function finalize() external {
+        // can be used to finalize the exploit patten
+    }
+}

scripts/N5-BecomeMasterExploit.js

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+const hre = require("hardhat");
+const ethers = hre.ethers;
+const CHALLENGES = require("../challenge-addresses.js")
+
+const challengeAddress = CHALLENGES.N5BecomeMaster;
+const ETH_UNIT = ethers.utils.parseEther("0.0001");
+
+async function main() {
+    // command to run against fork
+    // npx hardhat run scripts/N5-BecomeMasterExploit.js 
+
+    // command to run against real network
+    // npx hardhat run scripts/N5-BecomeMasterExploit.js --network mumbai
+
+    /*let challengeInstance = await ethers.getContractFactory("N5BecomeMaster");
+    challengeInstance = await challengeInstance.deploy({ value: ETH_UNIT });
+    await challengeInstance.deployed();*/
+    const challengeInstance = await ethers.getContractAt(
+        "N5BecomeMaster",
+        challengeAddress
+    );
+
+    /* ------> user solution code starts here */
+
+    /* ------> user solution code ends here */
+
+    console.log(`Challenge balance `, await ethers.provider.getBalance(challengeInstance.address));
+
+}
+
+main()
+    .then(() => process.exit(0))
+    .catch(error => {
+        console.error(error);
+        process.exit(1);
+    });

test/N5-BecomeMaster-medium.js

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+const { expect } = require("chai");
+
+const CHALLENGES = require("../challenge-addresses.js")
+const challengeAddress = CHALLENGES.N5BecomeMaster;
+
+
+// run the test
+// npx hardhat test ./test/N5-BecomeMaster-medium.js --network mumbai
+describe("CTF #5 BecomeMaster", function () {
+    it("Should recover all funds", async function () {
+        const challengeInstance = await ethers.getContractAt(
+            "N5BecomeMaster",
+            challengeAddress
+        );
+        expect(await ethers.provider.getBalance(challengeInstance.address)).to.equal("0");
+    });
+});