170605、防止sql注入（二）

java filter防止sql注入攻击

原理，过滤所有请求中含有非法的字符，例如：, & <  select delete 等关键字，黑客可以利用这些字符进行注入攻击，原理是后台实现使用拼接字符串，案例

某个网站的登入验证的SQL查询代码为

strSQL = "SELECT * FROM users WHERE (name = ‘" + userName + "‘) and (pw = ‘"+ passWord +"‘);"

恶意填入

userName = "‘ OR ‘1‘=‘1";与passWord = "‘ OR ‘1‘=‘1";时，将导致原本的SQL字符串被填为
       strSQL = "SELECT * FROM users WHERE (name = ‘‘ OR ‘1‘=‘1‘) and (pw = ‘‘ OR ‘1‘=‘1‘);"

也就是实际上运行的SQL命令会变成下面这样的

strSQL = "SELECT * FROM users;"

因此达到无帐号密码，亦可登入网站。所以SQL注入攻击被俗称为黑客的填空游戏。

实现三个步骤：

1，编写filter

2，配置xml

3，配置error.jsp

filter代码:

package com.rick.ssm.common.filter;

import java.io.IOException;
import java.util.ArrayList;
import java.util.List;
import java.util.Map;
import java.util.Set;

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;

/**
* -------------------------------------------
* Title : SqlInjectFilter
* Description : 防止sql注入过滤器
* Create on : 2017年8月2日 下午2:21:17
* Copyright (C) strongunion
* @author RICK
* @版本号: V1.0
* -------------------------------------------
*/
public class SqlInjectFilter implements Filter{

private static List<String> invalidsql = new ArrayList<String>();
private static String error = "/error.jsp";
private static boolean debug = false;

@Override
public void init(FilterConfig filterConfig) throws ServletException {
String sql = filterConfig.getInitParameter("invalidsql");
String errorpage = filterConfig.getInitParameter("error");
String de = filterConfig.getInitParameter("debug");
if(errorpage != null){
error = errorpage;
}
if (sql != null) {
String[] sqlarr = sql.split(" ");
for (String sqlword : sqlarr) {
invalidsql.add(sqlword);
}
invalidsql.add("<");
invalidsql.add(">");
}
if(de != null && Boolean.parseBoolean(de)){
debug = true;
System.out.println("PreventSQLInject Filter staring...");
System.out.println("print filter details");
System.out.println("invalid words as fllows (split with blank):");
for(String s : invalidsql){
System.out.print(s + " ");
}
System.out.println();
System.out.println("error page as fllows");
System.out.println(error);
System.out.println();
}
}

@Override
public void doFilter(ServletRequest req, ServletResponse res, FilterChain chain)
throws IOException, ServletException {
if(debug){
System.out.println("prevent sql inject filter works");
}
HttpServletRequest request = (HttpServletRequest)req;
HttpServletResponse response = (HttpServletResponse)res;
Map<String, String[]> params = request.getParameterMap();
Set<String> keys = params.keySet();
for(String key : keys){
String value = request.getParameter(key);
if(debug){
System.out.println("process params <key, value>: <"+key+", "+value+">");
}
for(String word : invalidsql){
if(word.equalsIgnoreCase(value) || value.contains(word)){
if(value.contains("<")){
value = value.replace("<", "<");
}
if(value.contains(">")){
value = value.replace(">", ">");
}
request.getSession().setAttribute("sqlInjectError", "您输入的参数值  \""+value+"\" 中包含关键字: \""+word+"\"");
response.sendRedirect(request.getContextPath()+error);
return;
}
}
}
chain.doFilter(req, res);
}

@Override
public void destroy() {
// TODO Auto-generated method stub
}
}

2.web.xml中添加如下配置：

<filter>
    <filter-name>PreventSqlInject</filter-name>
    <filter-class>cn.kepu.filter.SqlInjectFilter</filter-class>
    <!-- filter word, split with blank -->
    <init-param>
        <param-name>invalidsql</param-name>
        <param-value>select insert delete from update create destory drop alter and or like exec count chr mid master truncate char declare ; - ‘ %</param-value>
    </init-param>
    <!-- error page -->
    <init-param>
        <param-name>error</param-name>
        <param-value>/error.jsp</param-value>
    </init-param>
    <!-- debug -->
    <init-param>
        <param-name>debug</param-name>
        <param-value>true</param-value>
    </init-param>
  </filter>
  <filter-mapping>
    <filter-name>PreventSqlInject</filter-name>
    <url-pattern>/*</url-pattern>
  </filter-mapping> 

3，在根目录下添加error.jsp

<%@ page language="java" import="java.util.*" pageEncoding="utf-8"%>
<%
String path = request.getContextPath();
%>
<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN">
<html>
  <head>
    <title>防sql注入系统</title>
  </head> 

  <body>
    这个是防sql注入系统，自动过滤您的请求，请更换请求字符串。
    <%=session.getAttribute("sqlInjectError")%>
    <p><a href="<%=path%>">点此返回</a></p>
  </body>
</html>