{"id":2688,"date":"2024-08-19T22:06:00","date_gmt":"2024-08-19T14:06:00","guid":{"rendered":"https:\/\/systw.net\/note\/?p=2688"},"modified":"2025-08-23T21:25:38","modified_gmt":"2025-08-23T13:25:38","slug":"ctf-fallback","status":"publish","type":"post","link":"https:\/\/systw.net\/note\/archives\/2688","title":{"rendered":"CTF Fallback"},"content":{"rendered":"\n<p>\u9019\u9053 Blockchain CTF \u984c\u76ee\u6d89\u53ca\u4e00\u500b\u4ee5\u592a\u574a\u667a\u80fd\u5408\u7d04\u7684fallback\u6f0f\u6d1e\u5229\u7528\uff0c\u76ee\u6a19\u662f\u901a\u904e\u7279\u5b9a\u7684\u64cd\u4f5c\u5e8f\u5217\u7372\u5f97\u9019\u500b\u5408\u7d04\u7684\u6240\u6709\u6b0a\u4e26\u628a\u5408\u7d04\u7684\u9918\u984d\u6b78\u96f6\u3002<\/p>\n\n\n\n<p>\u984c\u76ee\u4f4d\u7f6e\uff1a<a href=\"https:\/\/ethernaut.openzeppelin.com\/level\/1\" target=\"_blank\" rel=\"noopener\">https:\/\/ethernaut.openzeppelin.com\/level\/1<\/a><\/p>\n\n\n\n<p>\u9019\u985e\u6f0f\u6d1e\u5728\u65e9\u671f\u7684\u4ee5\u592a\u574a\u667a\u80fd\u5408\u7d04\u4e2d\u8f03\u70ba\u5e38\u898b\uff0c\u5c24\u5176\u662f\u5728\u56de\u9000\u51fd\u6578\uff08\u5982 <code>receive<\/code> \u6216 <code>fallback<\/code>\uff09\u7684\u8a2d\u8a08\u4e0a\u3002\u90192\u51fd\u6578\u5728\u8655\u7406\u672a\u6307\u5b9a\u51fd\u6578\u7684\u8abf\u7528\u6216\u7d14\u4ee5\u592a\u5e63\u8f49\u8cec\u6642\u975e\u5e38\u654f\u611f\uff0c\u61c9\u8b39\u614e\u8a2d\u8a08\u5176\u908f\u8f2f\u3002<\/p>\n\n\n\n<hr class=\"wp-block-separator has-alpha-channel-opacity is-style-dots\"\/>\n\n\n\n<h2 class=\"wp-block-heading\">\u984c\u76ee\u8aaa\u660e<\/h2>\n\n\n\n<p>Look carefully at the contract&#8217;s code below. You will beat this level if<\/p>\n\n\n\n<ol class=\"wp-block-list\">\n<li>you claim ownership of the contract<\/li>\n\n\n\n<li>you reduce its balance to 0<\/li>\n<\/ol>\n\n\n\n<pre class=\"wp-block-code\"><code>\/\/ SPDX-License-Identifier: MIT\npragma solidity ^0.8.0;\n\ncontract Fallback {\n    mapping(address => uint256) public contributions;\n    address public owner;\n\n    constructor() {\n        owner = msg.sender;\n        contributions&#91;msg.sender] = 1000 * (1 ether);\n    }\n\n    modifier onlyOwner() {\n        require(msg.sender == owner, \"caller is not the owner\");\n        _;\n    }\n\n    function contribute() public payable {\n        require(msg.value &lt; 0.001 ether);\n        contributions&#91;msg.sender] += msg.value;\n        if (contributions&#91;msg.sender] > contributions&#91;owner]) {\n            owner = msg.sender;\n        }\n    }\n\n    function getContribution() public view returns (uint256) {\n        return contributions&#91;msg.sender];\n    }\n\n    function withdraw() public onlyOwner {\n        payable(owner).transfer(address(this).balance);\n    }\n\n    receive() external payable {\n        require(msg.value > 0 &amp;&amp; contributions&#91;msg.sender] > 0);\n        owner = msg.sender;\n    }\n}<\/code><\/pre>\n\n\n\n<hr class=\"wp-block-separator has-alpha-channel-opacity is-style-dots\"\/>\n\n\n\n<h3 class=\"wp-block-heading\">\u5408\u7d04\u5206\u6790<\/h3>\n\n\n\n<p>\u9019\u662f\u4e00\u500b\u540d\u70ba <code>Fallback<\/code> \u7684 Solidity \u5408\u7d04\uff0c\u5305\u542b\u4ee5\u4e0b\u95dc\u9375\u529f\u80fd\uff1a<\/p>\n\n\n\n<ul class=\"wp-block-list\">\n<li><strong>\u72c0\u614b\u8b8a\u91cf<\/strong>\uff1a\n<ul class=\"wp-block-list\">\n<li><code>mapping(address => uint256) public contributions<\/code>\uff1a\u8a18\u9304\u6bcf\u500b\u5730\u5740\u7684\u8ca2\u737b\u91cf\uff08\u4ee5 wei \u70ba\u55ae\u4f4d\uff09\u3002<\/li>\n\n\n\n<li><code>address public owner<\/code>\uff1a\u8a18\u9304\u5408\u7d04\u7684\u7576\u524d\u64c1\u6709\u8005\u3002<\/li>\n<\/ul>\n<\/li>\n<\/ul>\n\n\n\n<pre class=\"wp-block-code\"><code>contract Fallback {\n    mapping(address => uint256) public contributions;\n    address public owner;<\/code><\/pre>\n\n\n\n<ul class=\"wp-block-list\">\n<li><strong>\u69cb\u9020\u51fd\u6578 (<code>constructor<\/code>)<\/strong>\uff1a\n<ul class=\"wp-block-list\">\n<li>\u5728\u90e8\u7f72\u5408\u7d04\u6642\uff0c\u5c07\u90e8\u7f72\u8005\u7684\u5730\u5740\u8a2d\u7f6e\u70ba <code>owner<\/code>\u3002<\/li>\n\n\n\n<li>\u70ba\u90e8\u7f72\u8005\u521d\u59cb\u5316 <code>contributions[msg.sender] = 1000 ether<\/code>\u3002<\/li>\n<\/ul>\n<\/li>\n<\/ul>\n\n\n\n<pre class=\"wp-block-code\"><code>    constructor() {\n        owner = msg.sender;\n        contributions&#91;msg.sender] = 1000 * (1 ether);\n    }<\/code><\/pre>\n\n\n\n<ul class=\"wp-block-list\">\n<li><strong><code>contribute<\/code> \u51fd\u6578<\/strong>\uff1a\n<ul class=\"wp-block-list\">\n<li>\u5141\u8a31\u7528\u6236\u901a\u904e\u767c\u9001\u4ee5\u592a\u5e63\uff08ETH\uff09\u9032\u884c\u8ca2\u737b\uff0c\u4f46\u8981\u6c42 <code>msg.value &lt; 0.001 ether<\/code>\uff08\u5373\u5c0f\u65bc 0.001 ETH\uff09\u3002<\/li>\n\n\n\n<li>\u5c07\u767c\u9001\u7684 <code>msg.value<\/code> \u7d2f\u52a0\u5230 <code>contributions[msg.sender]<\/code>\u3002<\/li>\n\n\n\n<li>\u5982\u679c\u67d0\u5730\u5740\u7684\u8ca2\u737b\u91cf\u8d85\u904e\u7576\u524d <code>owner<\/code> \u7684\u8ca2\u737b\u91cf\uff08<code>contributions[owner]<\/code>\uff09\uff0c\u5247\u8a72\u5730\u5740\u6210\u70ba\u65b0\u7684 <code>owner<\/code>\u3002<\/li>\n<\/ul>\n<\/li>\n<\/ul>\n\n\n\n<pre class=\"wp-block-code\"><code>    function contribute() public payable {\n        require(msg.value &lt; 0.001 ether);\n        contributions&#91;msg.sender] += msg.value;\n        if (contributions&#91;msg.sender] > contributions&#91;owner]) {\n            owner = msg.sender;\n        }\n    }<\/code><\/pre>\n\n\n\n<ul class=\"wp-block-list\">\n<li><strong><code>getContribution<\/code> \u51fd\u6578<\/strong>\uff1a\n<ul class=\"wp-block-list\">\n<li>\u8fd4\u56de\u8abf\u7528\u8005\u7684\u8ca2\u737b\u91cf <code>contributions[msg.sender]<\/code>\u3002<\/li>\n<\/ul>\n<\/li>\n<\/ul>\n\n\n\n<pre class=\"wp-block-code\"><code>    function getContribution() public view returns (uint256) {\n        return contributions&#91;msg.sender];\n    }<\/code><\/pre>\n\n\n\n<ul class=\"wp-block-list\">\n<li><strong><code>withdraw<\/code> \u51fd\u6578<\/strong>\uff1a\n<ul class=\"wp-block-list\">\n<li>\u50c5\u9650 <code>owner<\/code> \u8abf\u7528\uff08\u901a\u904e <code>onlyOwner<\/code> \u4fee\u98fe\u7b26\u6aa2\u67e5\uff09\u3002<\/li>\n\n\n\n<li>\u5c07\u5408\u7d04\u7684\u5168\u90e8\u9918\u984d\u8f49\u79fb\u7d66 <code>owner<\/code>\u3002<\/li>\n<\/ul>\n<\/li>\n<\/ul>\n\n\n\n<pre class=\"wp-block-code\"><code>    function withdraw() public onlyOwner {\n        payable(owner).transfer(address(this).balance);\n    }<\/code><\/pre>\n\n\n\n<ul class=\"wp-block-list\">\n<li><strong><code>receive<\/code> \u51fd\u6578<\/strong>\uff1a\n<ul class=\"wp-block-list\">\n<li>\u9019\u662f\u4e00\u500b\u56de\u9000\u51fd\u6578\uff0c\u7576\u5408\u7d04\u6536\u5230\u4ee5\u592a\u5e63\u4f46\u672a\u6307\u5b9a\u5177\u9ad4\u51fd\u6578\u6642\u89f8\u767c\u3002<\/li>\n\n\n\n<li>\u8981\u6c42 <code>msg.value > 0<\/code>\uff08\u767c\u9001\u7684\u4ee5\u592a\u5e63\u5927\u65bc 0\uff09\u4e14 <code>contributions[msg.sender] > 0<\/code>\uff08\u8abf\u7528\u8005\u5fc5\u9808\u6709\u904e\u8ca2\u737b\uff09\u3002<\/li>\n\n\n\n<li>\u5c07 <code>owner<\/code> \u8a2d\u7f6e\u70ba <code>msg.sender<\/code>\u3002<\/li>\n<\/ul>\n<\/li>\n<\/ul>\n\n\n\n<pre class=\"wp-block-code\"><code>    receive() external payable {\n        require(msg.value > 0 &amp;&amp; contributions&#91;msg.sender] > 0);\n        owner = msg.sender;\n    }<\/code><\/pre>\n\n\n\n<hr class=\"wp-block-separator has-alpha-channel-opacity is-style-dots\"\/>\n\n\n\n<h3 class=\"wp-block-heading\">\u6f0f\u6d1e\u5206\u6790<\/h3>\n\n\n\n<p>\u67092\u7a2e\u65b9\u5f0f\u53ef\u4ee5\u6210\u70ba<code>owner<\/code><\/p>\n\n\n\n<figure class=\"wp-block-table\"><table class=\"has-fixed-layout\"><thead><tr><td>\u65b9\u6cd5<\/td><td>\u512a\u9ede<\/td><td>\u7f3a\u9ede<\/td><\/tr><\/thead><tbody><tr><td><strong>\u5229\u7528 <code>contribute()<\/code> (\u5408\u6cd5\u8def\u5f91)<\/strong><\/td><td>\u7b26\u5408\u5408\u7d04\u7684\u8a2d\u8a08\u908f\u8f2f\uff0c\u4e0d\u9700\u8981\u5229\u7528 <code>receive<\/code> \u51fd\u6578\u3002<\/td><td><strong>\u6210\u672c\u975e\u5e38\u9ad8\u6602<\/strong>\u3002\u70ba\u4e86\u8d85\u904e\u521d\u59cb\u7684 <code>1000 ether<\/code>\uff0c\u653b\u64ca\u8005\u9700\u8981\u6295\u5165\u5927\u91cf\u7684\u8cc7\u91d1\uff0c\u624b\u7e8c\u8cbb\u6210\u672c\u4e5f\u76f8\u7576\u9ad8\u3002<\/td><\/tr><tr><td><strong>\u5229\u7528 <code>receive()<\/code> (\u6f0f\u6d1e\u8def\u5f91)<\/strong><\/td><td><strong>\u6210\u672c\u6975\u4f4e<\/strong>\u3002\u53ea\u9700\u8981\u5148\u82b1\u4e00\u9ede\u9ede\u9322\u6210\u70ba <code>contributor<\/code> (\u4f8b\u5982 0.0001 <code>ether<\/code>)\uff0c\u518d\u767c\u9001\u4e00\u7b46\u7d14 ETH \u4ea4\u6613\u5c31\u53ef\u4ee5\u76f4\u63a5\u596a\u6b0a\u3002<\/td><td>\u5229\u7528\u4e86\u5408\u7d04\u7684\u6f0f\u6d1e\uff0c\u653b\u64ca\u884c\u70ba\u4e0d\u7b26\u5408\u8a2d\u8a08\u8005\u7684\u9810\u671f\u3002<\/td><\/tr><\/tbody><\/table><\/figure>\n\n\n\n<p>\u5177\u9ad4\u4f86\u8aaa\uff0c<code>receive<\/code> \u51fd\u6578\u5141\u8a31\u4efb\u4f55\u6eff\u8db3\u4ee5\u4e0b\u689d\u4ef6\u7684\u5730\u5740\u76f4\u63a5\u6210\u70ba <code>owner<\/code>\uff1a<\/p>\n\n\n\n<ul class=\"wp-block-list\">\n<li>\u767c\u9001\u7684\u4ee5\u592a\u5e63\u5927\u65bc 0\uff08<code>msg.value > 0<\/code>\uff09\u3002<\/li>\n\n\n\n<li>\u8a72\u5730\u5740\u7684\u8ca2\u737b\u91cf\u5927\u65bc 0\uff08<code>contributions[msg.sender] > 0<\/code>\uff09\u3002<\/li>\n<\/ul>\n\n\n\n<p>\u9019\u610f\u5473\u8457\uff0c\u53ea\u8981\u4e00\u500b\u5730\u5740\u5148\u901a\u904e <code>contribute<\/code> \u51fd\u6578\u8ca2\u737b\u4e86\u4e00\u5b9a\u91cf\u7684\u4ee5\u592a\u5e63\uff08\u4f7f\u5f97 <code>contributions[msg.sender] &gt; 0<\/code>\uff09\uff0c\u7136\u5f8c\u76f4\u63a5\u5411\u5408\u7d04\u767c\u9001\u4efb\u610f\u91d1\u984d\u7684\u4ee5\u592a\u5e63\uff08\u4f8b\u5982 1 wei\uff09\uff0c\u5c31\u80fd\u89f8\u767c <code>receive<\/code> \u51fd\u6578\u4e26\u6210\u70ba <code>owner<\/code>\u3002\u9019\u662f\u4e00\u500b\u986f\u8457\u7684\u8a2d\u8a08\u7f3a\u9677\uff0c\u56e0\u70ba <code>receive<\/code> \u51fd\u6578\u7684\u6aa2\u67e5\u689d\u4ef6\u904e\u65bc\u5bec\u9b06\uff0c\u6c92\u6709\u8003\u616e\u8ca2\u737b\u91cf\u7684\u591a\u5c11\u6216\u8207\u7576\u524d <code>owner<\/code> \u7684\u6bd4\u8f03\u3002<\/p>\n\n\n\n<p>\u76f8\u6bd4\u4e4b\u4e0b\uff0c<code>contribute<\/code> \u51fd\u6578\u8981\u6c42\u8ca2\u737b\u91cf\u8d85\u904e <code>owner<\/code> \u7684\u8ca2\u737b\u91cf\uff08<code>contributions[owner]<\/code>\uff0c\u521d\u59cb\u70ba 1000 ETH\uff09\u624d\u80fd\u6539\u8b8a\u6240\u6709\u6b0a\uff0c\u9019\u5c0d\u65bc\u653b\u64ca\u8005\u4f86\u8aaa\u96e3\u5ea6\u8f03\u9ad8\uff08\u9700\u8981\u8ca2\u737b\u8d85\u904e 1000 ETH\uff09\u3002\u800c <code>receive<\/code> \u51fd\u6578\u7e5e\u904e\u4e86\u9019\u500b\u9650\u5236\uff0c\u53ea\u9700\u6eff\u8db3\u5169\u500b\u7c21\u55ae\u689d\u4ef6\u5373\u53ef\u596a\u53d6\u6240\u6709\u6b0a\u3002<\/p>\n\n\n\n<hr class=\"wp-block-separator has-alpha-channel-opacity is-style-wide\"\/>\n\n\n\n<h2 class=\"wp-block-heading\">\u89e3\u7b54\u6b65\u9a5f\u8a73\u89e3<\/h2>\n\n\n\n<p>\u4ee5\u4e0b\u9010\u884c\u5206\u6790\u9019\u4e9b\u64cd\u4f5c\u5982\u4f55\u5229\u7528\u6f0f\u6d1e\u4e26\u9054\u6210\u76ee\u6a19\uff1a<\/p>\n\n\n\n<h3 class=\"wp-block-heading\">1. \u8abf\u7528 <code>contribute<\/code> \u51fd\u6578\uff0c\u5411\u5408\u7d04\u767c\u9001 1 wei\uff08\u4ee5\u592a\u574a\u7684\u6700\u5c0f\u55ae\u4f4d\uff09<\/h3>\n\n\n\n<ul class=\"wp-block-list\">\n<li><strong>\u64cd\u4f5c<\/strong>\uff1a<code>await contract.contribute({value: 1})<\/code><\/li>\n\n\n\n<li><strong>\u6548\u679c<\/strong>\uff1a\n<ul class=\"wp-block-list\">\n<li><code>contribute<\/code> \u51fd\u6578\u6aa2\u67e5 <code>msg.value &lt; 0.001 ether<\/code>\uff08\u5373 10^15 wei\uff09\u3002\u7531\u65bc 1 wei \u9060\u5c0f\u65bc 0.001 ETH\uff0c\u689d\u4ef6\u6eff\u8db3\u3002<\/li>\n\n\n\n<li>\u5408\u7d04\u5c07 <code>msg.value<\/code>\uff081 wei\uff09\u7d2f\u52a0\u5230 <code>contributions[msg.sender]<\/code>\uff0c\u56e0\u6b64 <code>contributions[msg.sender] = 1<\/code>\u3002<\/li>\n\n\n\n<li>\u6aa2\u67e5 <code>contributions[msg.sender] > contributions[owner]<\/code>\u3002\u521d\u59cb <code>owner<\/code> \u7684\u8ca2\u737b\u91cf\u70ba <code>1000 ether<\/code>\uff0810^21 wei\uff09\uff0c\u800c <code>contributions[msg.sender] = 1 wei<\/code>\uff0c\u56e0\u6b64\u4e0d\u6eff\u8db3\u689d\u4ef6\uff0c<code>owner<\/code> \u4e0d\u8b8a\u3002<\/li>\n<\/ul>\n<\/li>\n\n\n\n<li><strong>\u76ee\u7684<\/strong>\uff1a\u9019\u4e00\u6b65\u7684\u76ee\u7684\u662f\u6eff\u8db3 <code>receive<\/code> \u51fd\u6578\u7684\u689d\u4ef6\u4e4b\u4e00\uff1a<code>contributions[msg.sender] > 0<\/code>\u3002\u901a\u904e\u8ca2\u737b 1 wei\uff0c\u653b\u64ca\u8005\u7684\u5730\u5740\u5728 <code>contributions<\/code> \u6620\u5c04\u4e2d\u6709\u4e86\u975e\u96f6\u8a18\u9304\u3002<\/li>\n<\/ul>\n\n\n\n<p>\u53ef\u4ee5\u7528\u4ee5\u4e0b\u6307\u4ee4\u767c\u73fe\uff0c\u5728\u667a\u80fd\u5408\u7d04\u7684\u5730\u5740\u4e0a\uff0c\u91d1\u984d\u5df1\u5927\u65bc0 <\/p>\n\n\n\n<pre class=\"wp-block-code\"><code>contract.getContribution() <\/code><\/pre>\n\n\n\n<p><\/p>\n\n\n\n<h3 class=\"wp-block-heading\">2. \u76f4\u63a5\u5411\u5408\u7d04\u5730\u5740\u767c\u9001 1 wei \u7684\u4ee5\u592a\u5e63\uff0c\u89f8\u767c\u5408\u7d04\u7684 <code>receive<\/code> \u51fd\u6578<\/h3>\n\n\n\n<ul class=\"wp-block-list\">\n<li><strong>\u64cd\u4f5c<\/strong>\uff1a<code>await contract.sendTransaction({value: 1})<\/code><\/li>\n\n\n\n<li><strong>\u6548\u679c<\/strong>\uff1a\n<ul class=\"wp-block-list\">\n<li><code>receive<\/code> \u51fd\u6578\u6aa2\u67e5\u5169\u500b\u689d\u4ef6\uff1a\n<ul class=\"wp-block-list\">\n<li><code>msg.value > 0<\/code>\uff1a\u767c\u9001\u4e86 1 wei\uff0c\u6eff\u8db3\u689d\u4ef6\u3002<\/li>\n\n\n\n<li><code>contributions[msg.sender] > 0<\/code>\uff1a\u7531\u65bc\u4e0a\u4e00\u6b65\u7684 <code>contribute<\/code> \u64cd\u4f5c\uff0c<code>contributions[msg.sender] = 1<\/code>\uff0c\u6eff\u8db3\u689d\u4ef6\u3002<\/li>\n<\/ul>\n<\/li>\n\n\n\n<li>\u689d\u4ef6\u6eff\u8db3\u5f8c\uff0c<code>receive<\/code> \u51fd\u6578\u57f7\u884c <code>owner = msg.sender<\/code>\uff0c\u5c07\u653b\u64ca\u8005\u7684\u5730\u5740\u8a2d\u7f6e\u70ba\u65b0\u7684 <code>owner<\/code>\u3002<\/li>\n<\/ul>\n<\/li>\n\n\n\n<li><strong>\u76ee\u7684<\/strong>\uff1a\u9019\u4e00\u6b65\u5229\u7528\u4e86 <code>receive<\/code> \u51fd\u6578\u7684\u6f0f\u6d1e\uff0c\u76f4\u63a5\u5c07\u653b\u64ca\u8005\u8a2d\u70ba <code>owner<\/code>\uff0c\u7121\u9700\u6eff\u8db3 <code>contribute<\/code> \u51fd\u6578\u4e2d\u82db\u523b\u7684\u8ca2\u737b\u91cf\u6bd4\u8f03\u689d\u4ef6\u3002<\/li>\n<\/ul>\n\n\n\n<p>\u57f7\u884c\u5b8c <code>await contract.sendTransaction({value: 1})<\/code>\u5f8c\uff0c\u53ef\u4ee5\u57f7\u884c\u4ee5\u4e0b\u6307\u4ee4\u67e5\u770bowner\u72c0\u614b<\/p>\n\n\n\n<pre class=\"wp-block-code\"><code>await contract.owner()<\/code><\/pre>\n\n\n\n<p>\u53ef\u4ee5\u767c\u73feowner\u8b8a\u6210\u4f60\u7684eth address<\/p>\n\n\n\n<hr class=\"wp-block-separator has-alpha-channel-opacity is-style-dots\"\/>\n\n\n\n<h3 class=\"wp-block-heading\">\u4f7f\u7528sendTransaction\u7684\u539f\u56e0<\/h3>\n\n\n\n<p>\u5728\u667a\u80fd\u5408\u7d04\u7684\u7a0b\u5f0f\u78bc\u4e2d\uff0c\u78ba\u5be6\u6c92\u6709\u5b9a\u7fa9\u4e00\u500b\u540d\u70ba sendTransaction \u7684\u51fd\u6578\u3002\u9019\u662f\u56e0\u70ba sendTransaction \u4e0d\u662f\u5408\u7d04\u5167\u7684\u51fd\u6578\uff0c\u800c\u662f\u4ee5\u592a\u574a\u5ba2\u6236\u7aef\uff08\u5982 Web3.js \u6216 Ethers.js\uff09\u63d0\u4f9b\u7684\u4e00\u500b\u65b9\u6cd5\uff0c\u7528\u4f86\u5411\u667a\u80fd\u5408\u7d04\u767c\u9001\u4e00\u7b46\u4ea4\u6613\u3002\u5177\u9ad4\u4f86\u8aaa\uff0csendTransaction \u7528\u65bc\u76f4\u63a5\u5411\u5408\u7d04\u5730\u5740\u767c\u9001\u4ee5\u592a\u5e63\uff08ETH\uff09\uff0c\u800c\u4e0d\u8abf\u7528\u5408\u7d04\u4e2d\u7684\u4efb\u4f55\u7279\u5b9a\u51fd\u6578\u3002\u9019\u7a2e\u884c\u70ba\u6703\u89f8\u767c\u5408\u7d04\u7684<strong>\u56de\u9000\u51fd\u6578<\/strong>\uff08\u5728\u9019\u9053\u984c\u4e2d\u662f receive \u51fd\u6578\uff09\u3002<\/p>\n\n\n\n<p><\/p>\n\n\n\n<h3 class=\"wp-block-heading\">\u56de\u9000\u51fd\u6578<\/h3>\n\n\n\n<ol class=\"wp-block-list\"><\/ol>\n\n\n\n<p>\u5728 Solidity \u4e2d\uff0c\u56de\u9000\u51fd\u6578\u53ef\u4ee5\u901a\u904e\u5169\u7a2e\u65b9\u5f0f\u5b9a\u7fa9\uff1a<\/p>\n\n\n\n<ul class=\"wp-block-list\">\n<li><strong>fallback \u51fd\u6578<\/strong>\uff1a\u986f\u5f0f\u5b9a\u7fa9\u70ba fallback() external [payable]\uff0c\u7528\u65bc\u8655\u7406\u7121\u6548\u51fd\u6578\u8abf\u7528\u6216\u7d14\u4ee5\u592a\u5e63\u8f49\u5e33\uff08\u5982\u679c\u6709 payable \u4fee\u98fe\u7b26\uff09\u3002<\/li>\n\n\n\n<li><strong>receive \u51fd\u6578<\/strong>\uff1a\u986f\u5f0f\u5b9a\u7fa9\u70ba receive() external payable\uff0c\u5c08\u9580\u7528\u65bc\u8655\u7406\u7d14\u4ee5\u592a\u5e63\u8f49\u5e33\uff08data \u5b57\u6bb5\u70ba\u7a7a\uff09\u3002<\/li>\n<\/ul>\n\n\n\n<p>\u9019\u5169\u500b\u51fd\u6578\u7d71\u7a31\u70ba\u300c\u56de\u9000\u51fd\u6578\u300d\uff0c\u56e0\u70ba\u5b83\u5011\u662f\u7576\u4ea4\u6613\u7121\u6cd5\u5339\u914d\u5408\u7d04\u4e2d\u7684\u5176\u4ed6\u51fd\u6578\u6642\u7684\u300c\u5f8c\u5099\u300d\u8655\u7406\u6a5f\u5236\u3002\u5340\u5225\u5728\u65bc\uff1a<\/p>\n\n\n\n<ul class=\"wp-block-list\">\n<li>receive \u5c08\u7528\u65bc\u7d14\u4ee5\u592a\u5e63\u8f49\u5e33\uff08data \u70ba\u7a7a\u4e14 msg.value > 0\uff09\u3002<\/li>\n\n\n\n<li>fallback \u66f4\u901a\u7528\uff0c\u53ef\u4ee5\u8655\u7406\u7121\u6548\u51fd\u6578\u8abf\u7528\u6216\u7d14\u4ee5\u592a\u5e63\u8f49\u5e33\uff08\u5982\u679c\u6a19\u8a18\u70ba payable\uff09\u3002<\/li>\n<\/ul>\n\n\n\n<p>\u5728\u4f60\u7684\u5408\u7d04\u7a0b\u5f0f\u78bc\u4e2d\uff0c\u53ea\u6709 receive \u51fd\u6578\uff1a<\/p>\n\n\n\n<pre class=\"wp-block-code\"><code>receive() external payable {\n    require(msg.value > 0 &amp;&amp; contributions&#91;msg.sender] > 0);\n    owner = msg.sender;\n}<\/code><\/pre>\n\n\n\n<p>\u9019\u610f\u5473\u8457\uff0c\u7576\u5408\u7d04\u6536\u5230\u4e00\u7b46\u7d14\u4ee5\u592a\u5e63\u8f49\u5e33\uff08data \u70ba\u7a7a\uff0cmsg.value &gt; 0\uff09\u6642\uff0creceive \u51fd\u6578\u6703\u88ab\u89f8\u767c\u3002\u96d6\u7136\u7a0b\u5f0f\u78bc\u4e2d\u6c92\u6709 fallback \u9019\u500b\u8a5e\uff0c\u4f46 receive \u51fd\u6578\u672c\u8eab\u5c31\u662f\u4e00\u7a2e\u7279\u6b8a\u7684\u56de\u9000\u51fd\u6578\uff0c\u5c08\u9580\u8655\u7406\u7d14\u4ee5\u592a\u5e63\u8f49\u5e33\u7684\u60c5\u6cc1\u3002<\/p>\n\n\n\n<p><\/p>\n\n\n\n<h3 class=\"wp-block-heading\"> sendTransaction \u89f8\u767c receive \u51fd\u6578\u904e\u7a0b<\/h3>\n\n\n\n<ol start=\"2\" class=\"wp-block-list\"><\/ol>\n\n\n\n<p>\u7576\u4f60\u4f7f\u7528 await contract.sendTransaction({value: 1}) \u6642\uff0c\u5be6\u969b\u4e0a\u662f\u5728\u901a\u904e\u5ba2\u6236\u7aef\u5eab\uff08\u5982 Ethers.js\uff09\u5411\u5408\u7d04\u5730\u5740\u767c\u9001\u4e00\u7b46\u4ea4\u6613\u3002\u9019\u7b46\u4ea4\u6613\u7684\u7279\u9ede\u662f\uff1a<\/p>\n\n\n\n<ul class=\"wp-block-list\">\n<li><strong>\u76ee\u6a19\u5730\u5740<\/strong>\uff1a\u5408\u7d04\u5730\u5740\u3002<\/li>\n\n\n\n<li><strong>\u91d1\u984d<\/strong>\uff1a1 wei\uff08\u7531 value: 1 \u6307\u5b9a\uff09\u3002<\/li>\n\n\n\n<li><strong>\u6578\u64da\u5b57\u6bb5 (data)<\/strong>\uff1a\u70ba\u7a7a\uff08\u56e0\u70ba sendTransaction \u6c92\u6709\u6307\u5b9a\u8abf\u7528\u4efb\u4f55\u5177\u9ad4\u51fd\u6578\uff09\u3002<\/li>\n<\/ul>\n\n\n\n<p>\u5728\u4ee5\u592a\u574a\u865b\u64ec\u6a5f\uff08EVM\uff09\u7684\u57f7\u884c\u908f\u8f2f\u4e2d\uff0c\u7576\u4e00\u7b46\u4ea4\u6613\u7684 data \u5b57\u6bb5\u70ba\u7a7a\uff08\u5373\u4e0d\u8abf\u7528\u4efb\u4f55\u7279\u5b9a\u51fd\u6578\uff09\u4e14 msg.value &gt; 0\uff08\u767c\u9001\u4e86\u4ee5\u592a\u5e63\uff09\u6642\uff0cEVM \u6703\u6aa2\u67e5\u5408\u7d04\u662f\u5426\u5b9a\u7fa9\u4e86 receive \u51fd\u6578\uff1a<\/p>\n\n\n\n<ul class=\"wp-block-list\">\n<li>\u5982\u679c\u5408\u7d04\u6709 receive() external payable \u51fd\u6578\uff0c\u5247\u57f7\u884c\u8a72\u51fd\u6578\u3002<\/li>\n\n\n\n<li>\u5982\u679c\u6c92\u6709 receive \u51fd\u6578\uff0c\u4f46\u6709 fallback() external payable \u51fd\u6578\uff0c\u5247\u57f7\u884c fallback \u51fd\u6578\u3002<\/li>\n\n\n\n<li>\u5982\u679c\u5169\u8005\u90fd\u6c92\u6709\uff0c\u4e14\u4ea4\u6613\u767c\u9001\u4e86\u4ee5\u592a\u5e63\uff0c\u4ea4\u6613\u6703\u5931\u6557\uff08\u56de\u62cb\uff09\u3002<\/li>\n<\/ul>\n\n\n\n<p>\u5728\u9019\u9053\u984c\u7684\u5408\u7d04\u4e2d\uff0c\u56e0\u70ba\u5b9a\u7fa9\u4e86 receive \u51fd\u6578\uff1a<\/p>\n\n\n\n<p>\u7576\u4f60\u57f7\u884c await contract.sendTransaction({value: 1}) \u6642\uff1a<\/p>\n\n\n\n<ol class=\"wp-block-list\">\n<li>\u5ba2\u6236\u7aef\u5eab\u767c\u9001\u4e00\u7b46\u4ea4\u6613\u5230\u5408\u7d04\u5730\u5740\uff0c\u9644\u5e36 1 wei\uff0cdata \u5b57\u6bb5\u70ba\u7a7a\u3002<\/li>\n\n\n\n<li>EVM \u6aa2\u6e2c\u5230\u9019\u662f\u4e00\u7b46\u7d14\u4ee5\u592a\u5e63\u8f49\u5e33\uff08msg.value > 0\uff0cdata \u70ba\u7a7a\uff09\u3002<\/li>\n\n\n\n<li>EVM \u627e\u5230\u5408\u7d04\u4e2d\u7684 receive \u51fd\u6578\u4e26\u57f7\u884c\u5b83\u3002<\/li>\n\n\n\n<li>receive \u51fd\u6578\u6aa2\u67e5\uff1a\n<ul class=\"wp-block-list\">\n<li>msg.value > 0\uff1a1 wei \u6eff\u8db3\u689d\u4ef6\u3002<\/li>\n\n\n\n<li>contributions[msg.sender] > 0\uff1a\u7531\u65bc\u7b2c\u4e00\u6b65 contribute({value: 1}) \u5df2\u4f7f contributions[msg.sender] = 1\uff0c\u689d\u4ef6\u6eff\u8db3\u3002<\/li>\n<\/ul>\n<\/li>\n\n\n\n<li>\u57f7\u884c owner = msg.sender\uff0c\u5c07\u653b\u64ca\u8005\u7684\u5730\u5740\u8a2d\u70ba owner\u3002<\/li>\n<\/ol>\n\n\n\n<p>\u56e0\u6b64\uff0csendTransaction \u89f8\u767c\u4e86 receive \u51fd\u6578\uff0c\u56e0\u70ba\u5b83\u767c\u9001\u4e86\u4e00\u7b46\u7d14\u4ee5\u592a\u5e63\u8f49\u5e33\uff0c\u800c receive \u51fd\u6578\u6b63\u662f\u70ba\u9019\u7a2e\u60c5\u6cc1\u8a2d\u8a08\u7684\u3002<\/p>\n\n\n\n<p><\/p>\n\n\n\n<hr class=\"wp-block-separator has-alpha-channel-opacity is-style-dots\"\/>\n\n\n\n<h3 class=\"wp-block-heading\">3. \u8abf\u7528 <code>withdraw<\/code> \u51fd\u6578<\/h3>\n\n\n\n<ul class=\"wp-block-list\">\n<li><strong>\u64cd\u4f5c<\/strong>\uff1a<code>await contract.withdraw()<\/code><\/li>\n\n\n\n<li><strong>\u6548\u679c<\/strong>\uff1a\n<ul class=\"wp-block-list\">\n<li><code>withdraw<\/code> \u51fd\u6578\u6709 <code>onlyOwner<\/code> \u4fee\u98fe\u7b26\uff0c\u6aa2\u67e5 <code>msg.sender == owner<\/code>\u3002\u7531\u65bc\u4e0a\u4e00\u6b65\u5df2\u5c07 <code>owner<\/code> \u8a2d\u70ba\u653b\u64ca\u8005\u7684\u5730\u5740\uff0c\u689d\u4ef6\u6eff\u8db3\u3002<\/li>\n\n\n\n<li>\u5408\u7d04\u57f7\u884c <code>payable(owner).transfer(address(this).balance)<\/code>\uff0c\u5c07\u5408\u7d04\u7684\u5168\u90e8\u9918\u984d\u8f49\u79fb\u7d66\u653b\u64ca\u8005\u3002<\/li>\n<\/ul>\n<\/li>\n\n\n\n<li><strong>\u76ee\u7684<\/strong>\uff1a\u9019\u4e00\u6b65\u63d0\u53d6\u5408\u7d04\u4e2d\u7684\u6240\u6709\u4ee5\u592a\u5e63\uff0c\u5b8c\u6210\u653b\u64ca\u76ee\u6a19\u3002<\/li>\n<\/ul>\n\n\n\n<p><\/p>\n\n\n\n<hr class=\"wp-block-separator has-alpha-channel-opacity is-style-dots\"\/>\n\n\n\n<h3 class=\"wp-block-heading\">\u89e3\u7b54\u6b65\u9a5f\u6574\u7406\u5982\u4e0b<\/h3>\n\n\n\n<pre class=\"wp-block-code\"><code>await contract.contribute({value: 1})\nawait contract.sendTransaction({value: 1})\nawait contract.withdraw()<\/code><\/pre>\n\n\n\n<p>\u901a\u904e\u4ee5\u4e0b\u6b65\u9a5f\uff0c\u653b\u64ca\u8005\u5229\u7528\u4e86 <code>receive<\/code> \u51fd\u6578\u7684\u6f0f\u6d1e\uff1a<\/p>\n\n\n\n<ol class=\"wp-block-list\">\n<li>\u8abf\u7528 <code>contribute<\/code> \u767c\u9001 1 wei\uff0c\u4f7f\u5f97 <code>contributions[msg.sender] > 0<\/code>\u3002<\/li>\n\n\n\n<li>\u901a\u904e <code>sendTransaction<\/code> \u767c\u9001 1 wei \u89f8\u767c <code>receive<\/code> \u51fd\u6578\uff0c\u6210\u70ba <code>owner<\/code>\u3002<\/li>\n\n\n\n<li>\u8abf\u7528 <code>withdraw<\/code> \u63d0\u53d6\u5408\u7d04\u9918\u984d\u3002<\/li>\n<\/ol>\n","protected":false},"excerpt":{"rendered":"<p>\u9019\u9053 Blockchain CTF \u984c\u76ee\u6d89\u53ca\u4e00\u500b\u4ee5\u592a\u574a\u667a\u80fd\u5408\u7d04\u7684fallback\u6f0f\u6d1e\u5229\u7528\uff0c\u76ee\u6a19\u662f\u901a\u904e\u7279\u5b9a\u7684\u64cd\u4f5c\u5e8f\u5217\u7372\u5f97\u9019\u500b\u5408\u7d04\u7684\u6240\u6709\u6b0a\u4e26\u628a\u5408\u7d04\u7684\u9918\u984d\u6b78\u96f6\u3002<\/p>\n","protected":false},"author":1,"featured_media":0,"comment_status":"closed","ping_status":"closed","sticky":false,"template":"","format":"standard","meta":{"fifu_image_url":"","fifu_image_alt":"","_jetpack_memberships_contains_paid_content":false,"footnotes":"","jetpack_publicize_message":"","jetpack_publicize_feature_enabled":true,"jetpack_social_post_already_shared":false,"jetpack_social_options":{"image_generator_settings":{"template":"highway","default_image_id":0,"enabled":false},"version":2}},"categories":[371],"tags":[],"class_list":["post-2688","post","type-post","status-publish","format-standard","hentry","category-web3-security"],"jetpack_publicize_connections":[],"jetpack_featured_media_url":"","jetpack_sharing_enabled":true,"_links":{"self":[{"href":"https:\/\/systw.net\/note\/wp-json\/wp\/v2\/posts\/2688","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/systw.net\/note\/wp-json\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/systw.net\/note\/wp-json\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/systw.net\/note\/wp-json\/wp\/v2\/users\/1"}],"replies":[{"embeddable":true,"href":"https:\/\/systw.net\/note\/wp-json\/wp\/v2\/comments?post=2688"}],"version-history":[{"count":1,"href":"https:\/\/systw.net\/note\/wp-json\/wp\/v2\/posts\/2688\/revisions"}],"predecessor-version":[{"id":2712,"href":"https:\/\/systw.net\/note\/wp-json\/wp\/v2\/posts\/2688\/revisions\/2712"}],"wp:attachment":[{"href":"https:\/\/systw.net\/note\/wp-json\/wp\/v2\/media?parent=2688"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/systw.net\/note\/wp-json\/wp\/v2\/categories?post=2688"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/systw.net\/note\/wp-json\/wp\/v2\/tags?post=2688"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}