SQL注入简介
SQL注入是比较常见的网络攻击方式之一，它不是利用操作系统的BUG来实现攻击，而是针对程序员编程时的疏忽，通过SQL语句，实现无帐号登录，甚至篡改数据库。
SQL注入攻击实例
比如在一个登录界面，要求输入用户名和密码：
可以这样输入实现免帐号登录：
用户名： ‘or 1 = 1 –
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)
这是为什么呢? 下面我们分析一下：
从理论上说，后台认证程序中会有如下的SQL语句：
String sql = "select * from user_table where username=
' "+userName+" ' and password=' "+password+" '";
当输入了上面的用户名和密码，上面的SQL语句变成：
SELECT * FROM user_table WHERE username=
'’or 1 = 1 -- and password='’
分析SQL语句：
条件后面username=”or 1=1 用户名等于 ” 或1=1 那么这个条件一定会成功；
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。
这还是比较温柔的，如果是执行
SELECT * FROM user_table WHERE
username='' ;DROP DATABASE (DB Name) --' and password=''
….其后果可想而知…
应对方法1、配置web.xml
<!--过滤XSS注入 -->
<filter>
<filter-name>XssEscape</filter-name>
<filter-class>com.cm.contract.filter.XSSFilter.XssFilter</filter-class>
</filter>
<filter-mapping>
<filter-name>XssEscape</filter-name>
<url-pattern>/*</url-pattern>
<dispatcher>REQUEST</dispatcher>
</filter-mapping>
<!--过滤SQL注入 -->
<filter>
<filter-name>SqlFilter</filter-name>
<filter-class>com.cm.contract.filter.SQLFilter.SqlFilter</filter-class>
</filter>
<filter-mapping>
<filter-name>SqlFilter</filter-name>
<url-pattern>/*</url-pattern>
</filter-mapping>
2、SqlFilter.java
package com.cm.contract.filter.SQLFilter;
import java.io.IOException;
import java.util.Enumeration;
import javax.servlet.Filter;
import javax.servlet.FilterChain;
import javax.servlet.FilterConfig;
import javax.servlet.ServletException;
import javax.servlet.ServletRequest;
import javax.servlet.ServletResponse;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
/**
* 过滤sql关键字的Filter
* @author FengArWei
*/
public class SqlFilter implements Filter {
public void doFilter(ServletRequest request, ServletResponse response, FilterChain chain) throws IOException, ServletException {
HttpServletRequest req = (HttpServletRequest) request;
HttpServletResponse res = (HttpServletResponse) response;
//获得所有请求参数名
@SuppressWarnings("rawtypes")
Enumeration params = req.getParameterNames();
String sql = "";
while (params.hasMoreElements()) {
//得到参数名
String name = params.nextElement().toString();
//System.out.println("name===========================" + name + "--");
//得到参数对应值
String[] value = req.getParameterValues(name);
for (int i = 0; i < value.length; i++) {
sql = sql + value[i];
}
}
//System.out.println("============================SQL"+sql);
//有sql关键字，跳转到error.html
if (sqlValidate(sql)) {
res.sendRedirect("error.html");
//String ip = req.getRemoteAddr();
} else {
chain.doFilter(req, res);
}
}
//效验
protected static boolean sqlValidate(String str) {
str = str.toLowerCase();//统一转为小写
String badStr = "'|and|exec|execute|insert|create|drop|table|from|grant|use|group_concat|column_name|" +
"information_schema.columns|table_schema|union|where|select|delete|update|order|by|count|*|" +
"chr|mid|master|truncate|char|declare|or|;|-|--|+|,|like|//|/|%|#";//过滤掉的sql关键字，可以手动添加
String[] badStrs = badStr.split("|");
for (int i = 0; i < badStrs.length; i++) {
if (str.indexOf(badStrs[i]) !=-1) {
return true;
}
}
return false;
}
public void init(FilterConfig filterConfig) throws ServletException {
//throw new UnsupportedOperationException("Not supported yet.");
}
public void destroy() {
//throw new UnsupportedOperationException("Not supported yet.");
}
}
package com.cm.contract.filter.XSSFilter;
import java.io.IOException;
import javax.servlet.Filter;
import javax.servlet.FilterChain;
import javax.servlet.FilterConfig;
import javax.servlet.ServletException;
import javax.servlet.ServletRequest;
import javax.servlet.ServletResponse;
import javax.servlet.http.HttpServletRequest;
public class XssFilter implements Filter {
@Override
public void init(FilterConfig filterConfig) throws ServletException {
}
@Override
public void doFilter(ServletRequest request, ServletResponse response,
FilterChain chain) throws IOException, ServletException {
chain.doFilter(new XssHttpServletRequestWrapper((HttpServletRequest) request), response);
}
@Override
public void destroy() {
}
}
package com.cm.contract.filter.XSSFilter;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletRequestWrapper;
import org.apache.commons.lang3.StringEscapeUtils;
public class XssHttpServletRequestWrapper extends HttpServletRequestWrapper {
public XssHttpServletRequestWrapper(HttpServletRequest request) {
super(request);
}
@Override
public String getHeader(String name) {
return StringEscapeUtils.escapeHtml4(super.getHeader(name));
}
@Override
public String getQueryString() {
return StringEscapeUtils.escapeHtml4(super.getQueryString());
}
@Override
public String getParameter(String name) {
return StringEscapeUtils.escapeHtml4(super.getParameter(name));
}
@Override
public String[] getParameterValues(String name) {
String[] values = super.getParameterValues(name);
if(values != null) {
int length = values.length;
String[] escapseValues = new String[length];
for(int i = 0; i < length; i++){
escapseValues[i] = StringEscapeUtils.escapeHtml4(values[i]);
}
return escapseValues;
}
return super.getParameterValues(name);
}
} 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。
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