有效防止SQL注入的5种方法总结
<p><span><strong>sql注入入门</strong></span></p>
<p>
sql 注入是一类危害极大的攻击形式。虽然危害很大，但是防御却远远没有xss那么困难。</p>
<p>
sql 注入漏洞存在的原因，就是拼接 sql 参数。也就是将用于输入的查询参数，直接拼接在 sql 语句中，导致了sql 注入漏洞。</p>
<p>
<strong>演示下经典的sql注入</strong></p>
<p>
<img title="有效防止SQL注入的5种方法总结" alt="有效防止SQL注入的5种方法总结" src="https://zhuji.jb51.net/uploads/img/202305/7447258528a4678f05e5a96de6b73c3b.jpg"></p>
<p>
我们看到：<code>select id,no from user where id=2;</code></p>
<p>
如果该语句是通过sql字符串拼接得到的，比如： <code>string sql = "select id,no from user where id=" + id;</code></p>
<p>
其中的 id 是一个用户输入的参数，那么，如果用户输入的是 2， 那么上面看到查到了一条数据，如果用户输入的是<code> 2 or 1=1</code> 进行sql注入攻击, 那么看到，上面的语句(<code>select id,no from user where id=2 or 1=1;</code> )将user表中的所有记录都查出来了。 这就是典型的sql注入。</p>
<p>
<strong>再看一列：</strong></p>
<p>
<img title="有效防止SQL注入的5种方法总结" alt="有效防止SQL注入的5种方法总结" src="https://zhuji.jb51.net/uploads/img/202305/18afb92c11d8ff46db0eaa2250876175.jpg"></p>
<p>
我们看到通过 sql 注入能够直接将表 sqlinject 删除掉！可见其危害！</p>
<p>
<span><strong>sql注入攻击的总体思路</strong></span></p>
<p>
1、寻找到sql注入的位置</p>
<p>
2、判断服务器类型和后台数据库类型</p>
<p>
3、针对不通的服务器和数据库特点进行sql注入攻击</p>
<p>
<span><strong>sql注入攻击实例</strong></span></p>
<p>
<strong>比如在一个登录界面，要求输入用户名和密码：</strong></p>
<p>
可以这样输入实现免帐号登录：</p>
<p>
用户名： ‘or 1 = 1 –</p>
<p>
密 码：点登陆,如若没有做特殊处理,那么这个非法用户就很得意的登陆进去了.(当然现在的有些语言的数据库api已经处理了这些问题)</p>
<p>
<strong>这是为什么呢? 下面我们分析一下：</strong></p>
<p>
从理论上说，后台认证程序中会有如下的sql语句：</p>
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<code class="sql plain">string sql = </code><code class="sql string">"select * from user_table where username=' "</code><code class="sql plain">+username+</code><code class="sql string">" ' and password=' "</code><code class="sql plain">+</code><code class="sql keyword">password</code><code class="sql plain">+</code><code class="sql string">" '"</code><code class="sql plain">;</code>
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当输入了上面的用户名和密码，上面的sql语句变成：</p>
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<code class="sql keyword">select</code> <code class="sql plain">* </code><code class="sql keyword">from</code> <code class="sql plain">user_table </code><code class="sql keyword">where</code> <code class="sql plain">username=</code><code class="sql string">''</code><code class="sql color1">or</code> <code class="sql plain">1 = 1 </code><code class="sql comments">-- and password=''</code>
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<strong>分析sql语句：</strong></p>
<p>
条件后面<code>username=”or 1=1</code> 用户名等于 ” 或1=1 那么这个条件一定会成功；</p>
<p>
然后后面加两个-，这意味着注释，它将后面的语句注释，让他们不起作用，这样语句永远都能正确执行，用户轻易骗过系统，获取合法身份。</p>
<p>
这还是比较温柔的，如果是执行</p>
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<code class="sql keyword">select</code> <code class="sql plain">* </code><code class="sql keyword">from</code> <code class="sql plain">user_table </code><code class="sql keyword">where</code> <code class="sql plain">username=</code><code class="sql string">''</code> <code class="sql plain">;</code><code class="sql keyword">drop</code> <code class="sql keyword">database</code> <code class="sql plain">(db </code><code class="sql keyword">name</code><code class="sql plain">) </code><code class="sql comments">--' and password=''</code>
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….其后果可想而知…</p>
<p>
<span><strong>应对方法</strong></span></p>
<p>
下面我针对jsp，说一下应对方法：</p>
<p>
<strong>1.（简单又有效的方法）preparedstatement</strong></p>
<p>
采用预编译语句集，它内置了处理sql注入的能力，只要使用它的setxxx方法传值即可。</p>
<p>
使用好处：</p>
<p>
(1).代码的可读性和可维护性.</p>
<p>
(2).preparedstatement尽最大可能提高性能.</p>
<p>
(3).最重要的一点是极大地提高了安全性.</p>
<p>
原理：</p>
<p>
sql注入只对sql语句的准备(编译)过程有破坏作用</p>
<p>
而preparedstatement已经准备好了,执行阶段只是把输入串作为数据处理,</p>
<p>
而不再对sql语句进行解析,准备,因此也就避免了sql注入问题.</p>
<p>
<strong>2.使用正则表达式过滤传入的参数</strong></p>
<p>
要引入的包：</p>
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<code class="sql plain">import java.util.regex.*;</code>
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正则表达式：</p>
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<code class="sql plain">private string checksql = “^(.+)\\sand\\s(.+)|(.+)\\sor(.+)\\s$”;</code>
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判断是否匹配：</p>
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<code class="sql plain">pattern.matches(checksql,targerstr);</code>
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<strong>下面是具体的正则表达式：</strong></p>
<p>
检测sql meta-characters的正则表达式 ： <code>/(\%27)|(\')|(\-\-)|(\%23)|(#)/ix</code></p>
<p>
修正检测sql meta-characters的正则表达式 ： <code>/((\%3d)|(=))[^\n]*((\%27)|(\')|(\-\-)|(\%3b)|(:))/i</code></p>
<p>
典型的sql 注入攻击的正则表达式 ： <code>/\w*((\%27)|(\'))((\%6f)|o|(\%4f))((\%72)|r|(\%52))/ix</code></p>
<p>
检测sql注入，union查询关键字的正则表达式 ： <code>/((\%27)|(\'))union/ix(\%27)|(\')</code></p>
<p>
检测ms sql server sql注入攻击的正则表达式： <code>/exec(\s|\+)+(s|x)p\w+/ix</code></p>
<p>
等等…..</p>
<p>
<strong>3.字符串过滤</strong></p>
<p>
比较通用的一个方法：</p>
<p>
（||之间的参数可以根据自己程序的需要添加）</p>
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<code class="sql keyword">public</code> <code class="sql keyword">static</code> <code class="sql plain">boolean sql_inj(string str){</code>
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<code class="sql plain">string inj_str = </code><code class="sql string">"'|and|exec|insert|select|delete|update|</code>
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<code class="sql string">count|*|%|chr|mid|master|truncate|char|declare|;|or|-|+|,"</code><code class="sql plain">;</code>
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<code class="sql plain">string inj_stra[] = split(inj_str,</code><code class="sql string">"|"</code><code class="sql plain">);</code>
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<code class="sql keyword">for</code> <code class="sql plain">(</code><code class="sql keyword">int</code> <code class="sql plain">i=0 ; i < inj_stra.length ; i++ ){</code>
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<code class="sql plain">if (str.indexof(inj_stra)>=0){</code>
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<code class="sql keyword">return</code> <code class="sql keyword">true</code><code class="sql plain">;</code>
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<code class="sql plain">}</code>
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<code class="sql plain">}</code>
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<code class="sql keyword">return</code> <code class="sql keyword">false</code><code class="sql plain">;</code>
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<code class="sql plain">}</code>
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<p>
<strong>4.jsp中调用该函数检查是否包函非法字符</strong></p>
<p>
防止sql从url注入：</p>
<p>
sql_inj.java代码：</p>
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<code class="sql plain">package sql_inj;</code>
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<code class="sql plain">import java.net.*;</code>
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<code class="sql plain">import java.io.*;</code>
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<code class="sql plain">import java.sql.*;</code>
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<code class="sql plain">import java.text.*;</code>
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<code class="sql plain">import java.lang.string;</code>
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<code class="sql keyword">public</code> <code class="sql plain">class sql_inj{</code>
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<code class="sql keyword">public</code> <code class="sql keyword">static</code> <code class="sql plain">boolean sql_inj(string str){</code>
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<code class="sql plain">string inj_str = </code><code class="sql string">"'|and|exec|insert|select|delete|update|</code>
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<code class="sql string">count|*|%|chr|mid|master|truncate|char|declare|;|or|-|+|,"</code><code class="sql plain">;</code>
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<code class="sql plain">//这里的东西还可以自己添加</code>
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<code class="sql plain">string[] inj_stra=inj_str.split(</code><code class="sql string">"\\|"</code><code class="sql plain">);</code>
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<code class="sql keyword">for</code> <code class="sql plain">(</code><code class="sql keyword">int</code> <code class="sql plain">i=0 ; i < inj_stra.length ; i++ ){</code>
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<code class="sql plain">if (str.indexof(inj_stra)>=0){</code>
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<code class="sql keyword">return</code> <code class="sql keyword">true</code><code class="sql plain">;</code>
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<code class="sql plain">}</code>
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<code class="sql plain">}</code>
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<code class="sql keyword">return</code> <code class="sql keyword">false</code><code class="sql plain">;</code>
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<code class="sql plain">}</code>
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<code class="sql plain">}</code>
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<p>
<strong>5.jsp页面判断代码：</strong></p>
<p>
使用javascript在客户端进行不安全字符屏蔽</p>
<p>
功能介绍：检查是否含有”‘”,”\\”,”/”</p>
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参数说明：要检查的字符串</p>
<p>
返回值：0：是1：不是</p>
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函数名是</p>
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28</div>
<div class="line number29 index28 alt2">
29</div>
</td>
<td class="code">
<div class="container">
<div class="line number1 index0 alt2">
<code class="sql keyword">function</code> <code class="sql keyword">check</code><code class="sql plain">(a){</code>
</div>
<div class="line number2 index1 alt1">
</div>
<div class="line number3 index2 alt2">
<code class="sql keyword">return</code> <code class="sql plain">1;</code>
</div>
<div class="line number4 index3 alt1">
</div>
<div class="line number5 index4 alt2">
<code class="sql plain">fibdn = new array (”‘” ,”\\”,”/”);</code>
</div>
<div class="line number6 index5 alt1">
</div>
<div class="line number7 index6 alt2">
<code class="sql plain">i=fibdn.length;</code>
</div>
<div class="line number8 index7 alt1">
</div>
<div class="line number9 index8 alt2">
<code class="sql plain">j=a.length;</code>
</div>
<div class="line number10 index9 alt1">
</div>
<div class="line number11 index10 alt2">
<code class="sql keyword">for</code> <code class="sql plain">(ii=0; ii＜i; ii++)</code>
</div>
<div class="line number12 index11 alt1">
</div>
<div class="line number13 index12 alt2">
<code class="sql plain">{ </code><code class="sql keyword">for</code> <code class="sql plain">(jj=0; jj＜j; jj++)</code>
</div>
<div class="line number14 index13 alt1">
</div>
<div class="line number15 index14 alt2">
<code class="sql plain">{ temp1=a.charat(jj);</code>
</div>
<div class="line number16 index15 alt1">
</div>
<div class="line number17 index16 alt2">
<code class="sql plain">temp2=fibdn;</code>
</div>
<div class="line number18 index17 alt1">
</div>
<div class="line number19 index18 alt2">
<code class="sql plain">if (tem'; p1==temp2)</code>
</div>
<div class="line number20 index19 alt1">
</div>
<div class="line number21 index20 alt2">
<code class="sql plain">{ </code><code class="sql keyword">return</code> <code class="sql plain">0; }</code>
</div>
<div class="line number22 index21 alt1">
</div>
<div class="line number23 index22 alt2">
<code class="sql plain">}</code>
</div>
<div class="line number24 index23 alt1">
</div>
<div class="line number25 index24 alt2">
<code class="sql plain">}</code>
</div>
<div class="line number26 index25 alt1">
</div>
<div class="line number27 index26 alt2">
<code class="sql keyword">return</code> <code class="sql plain">1;</code>
</div>
<div class="line number28 index27 alt1">
</div>
<div class="line number29 index28 alt2">
<code class="sql plain">}</code>
</div>
</div>
</td>
</tr></tbody></table>
</div>
</div>
</div>
<p>
总的说来，防范一般的sql注入只要在代码规范上下点功夫就可以了。</p>
<p>
凡涉及到执行的sql中有变量时，用jdbc（或者其他数据持久层）提供的如：preparedstatement就可以 ，切记不要用拼接字符串的方法就可以了。</p>
<p>
<span><strong>总结</strong></span></p>
<p>
以上就是这篇文章的全部内容了，希望本文的内容对大家的学习或者工作能带来一定的帮助，如果有疑问大家可以留言交流。</p>
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