Tomcat Filter型内存马分析与实现教学文档<\/h1>

一、前言<\/h2>

Filter功能回顾<\/h3>
Filter（过滤器）是Java Web中的核心组件，用于在请求到达Servlet之前或响应返回客户端之前进行拦截处理。通过自定义过滤器可以实现请求修改、权限验证、日志记录等功能。<\/p>

内存马基本思路<\/h3>

内存Webshell的核心思想：动态创建恶意Filter并将其置于Filter链最前端，从而在请求处理的最早阶段执行恶意代码。<\/p>

攻击流程<\/strong>：<\/p>

请求首先经过恶意Filter<\/li>
恶意代码执行命令操作<\/li>
请求继续正常处理流程<\/li>
攻击者获得远程命令执行能力<\/li> <\/ol>
二、Tomcat Filter流程分析<\/h2>
环境搭建<\/h3>
技术栈<\/strong>：<\/p>

Tomcat 8.5.81<\/li>
Maven项目<\/li> <\/ul>
依赖配置<\/strong>：<\/p>
<dependency><\/span> <\/span><\/span> <groupId><\/span>org.apache.tomcat<\/groupId><\/span> <\/span><\/span> <artifactId><\/span>tomcat-websocket<\/artifactId><\/span> <\/span><\/span> <version><\/span>8.5.0<\/version><\/span> <\/span><\/span><\/dependency><\/span> <\/span><\/span><dependency><\/span> <\/span><\/span> <groupId><\/span>org.apache.tomcat<\/groupId><\/span> <\/span><\/span> <artifactId><\/span>tomcat-catalina<\/artifactId><\/span> <\/span><\/span> <version><\/span>8.5.0<\/version><\/span> <\/span><\/span><\/dependency><\/span> <\/span><\/span><\/code><\/pre>示例Filter实现<\/h3> import<\/span> javax.servlet.*;<\/span> <\/span><\/span>import<\/span> java.io.IOException;<\/span> <\/span><\/span> <\/span><\/span>public<\/span> class<\/span> filter<\/span> implements<\/span> Filter {<\/span> <\/span><\/span> @Override<\/span> <\/span><\/span> public<\/span> void<\/span> init<\/span>(<\/span>FilterConfig filterConfig)<\/span> throws<\/span> ServletException {<\/span> <\/span><\/span> System.<\/span>out<\/span>.<\/span>println<\/span>(<\/span>"Filter start"<\/span>);<\/span> <\/span><\/span> }<\/span> <\/span><\/span> <\/span><\/span> @Override<\/span> <\/span><\/span> public<\/span> void<\/span> doFilter<\/span>(<\/span>ServletRequest servletRequest,<\/span> <\/span><\/span> ServletResponse servletResponse,<\/span> <\/span><\/span> FilterChain filterChain)<\/span> <\/span><\/span> throws<\/span> IOException,<\/span> ServletException {<\/span> <\/span><\/span> System.<\/span>out<\/span>.<\/span>println<\/span>(<\/span>"Performed a filtering operation"<\/span>);<\/span> <\/span><\/span> filterChain.<\/span>doFilter<\/span>(<\/span>servletRequest,<\/span> servletResponse);<\/span> <\/span><\/span> }<\/span> <\/span><\/span> <\/span><\/span> @Override<\/span> <\/span><\/span> public<\/span> void<\/span> destroy<\/span>()<\/span> {<\/span> <\/span><\/span> \/\/ 清理资源 <\/span><\/span><\/span><\/span> }<\/span> <\/span><\/span>}<\/span> <\/span><\/span><\/code><\/pre>web.xml配置<\/h3> <?xml version="1.0" encoding="UTF-8"?><\/span> <\/span><\/span><web-app<\/span> xmlns=<\/span>"http:\/\/xmlns.jcp.org\/xml\/ns\/javaee"<\/span> <\/span><\/span> version=<\/span>"4.0"<\/span>><\/span> <\/span><\/span> <filter><\/span> <\/span><\/span> <filter-name><\/span>filter<\/filter-name><\/span> <\/span><\/span> <filter-class><\/span>filter<\/filter-class><\/span> <\/span><\/span> <\/filter><\/span> <\/span><\/span> <filter-mapping><\/span> <\/span><\/span> <filter-name><\/span>filter<\/filter-name><\/span> <\/span><\/span> <url-pattern><\/span>\/filter<\/url-pattern><\/span> <\/span><\/span> <\/filter-mapping><\/span> <\/span><\/span><\/web-app><\/span> <\/span><\/span><\/code><\/pre>三、Filter调用链深度分析<\/h2> 3.1 请求处理后的流程分析（\/filter访问后）<\/h3> 调用栈关键节点<\/strong>：<\/p> ApplicationFilterChain#doFilter()<\/strong><\/p> 安全检查：Globals.IS_SECURITY_ENABLED<\/code><\/li> 核心方法：internalDoFilter(request, response)<\/code><\/li> <\/ul> <\/li> Filter链处理机制<\/strong>：<\/p> \/\/ Filter链存储结构 <\/span><\/span><\/span><\/span>private<\/span> ApplicationFilterConfig[]<\/span> filters =<\/span> new<\/span> ApplicationFilterConfig[<\/span>0<\/span>];<\/span> <\/span><\/span> <\/span><\/span>\/\/ Filter逐个调用逻辑 <\/span><\/span><\/span><\/span>ApplicationFilterConfig filterConfig =<\/span> filters[<\/span>pos++];<\/span> <\/span><\/span>Filter filter =<\/span> filterConfig.<\/span>getFilter<\/span>();<\/span> <\/span><\/span>filter.<\/span>doFilter<\/span>(<\/span>request,<\/span> response,<\/span> this<\/span>);<\/span> <\/span><\/span><\/code><\/pre><\/li> 链式调用特点<\/strong>：<\/p> 每个Filter的doFilter()<\/code>中调用FilterChain.doFilter()<\/code>将触发下一个Filter<\/li> 最后一个Filter调用Servlet.service()<\/code>方法<\/li> 任意Filter未调用FilterChain.doFilter()<\/code>将终止流程<\/li> <\/ul> <\/li> <\/ol> 3.2 请求处理前的流程分析（\/filter访问前）<\/h3> Valve管道调用序列<\/strong>：<\/p> StandardEngineValve<\/strong> → 引擎级请求处理<\/li> AbstractAccessLogValve<\/strong> → 访问日志记录<\/li> StandardHostValve<\/strong> → 虚拟主机路由<\/li> ErrorReportValve<\/strong> → 错误报告生成<\/li> AuthenticatorBase<\/strong> → 身份验证处理<\/li> StandardContextValve<\/strong> → Web应用上下文处理<\/li> StandardWrapperValve<\/strong> → Servlet包装器处理<\/li> <\/ol> 关键类说明<\/strong>：<\/p> StandardWrapperValve<\/strong>：负责Servlet生命周期管理和请求分配<\/li> StandardContextValve<\/strong>：Web应用上下文验证和请求过滤<\/li> AuthenticatorBase<\/strong>：提供基础身份认证机制<\/li> <\/ul> 四、Filter内存马实现原理<\/h2> 4.1 核心技术要点<\/h3> 动态Filter注册<\/strong><\/p> 绕过web.xml静态配置<\/li> 运行时动态添加恶意Filter<\/li> <\/ul> <\/li> Filter链位置控制<\/strong><\/p> 将恶意Filter置于链首<\/li> 确保最先执行恶意代码<\/li> <\/ul> <\/li> 恶意代码注入<\/strong><\/p> 在doFilter()中嵌入命令执行逻辑<\/li> 保持Filter链正常传递<\/li> <\/ul> <\/li> <\/ol> 4.2 实现步骤<\/h3> 步骤1：获取StandardContext<\/strong><\/p> \/\/ 通过Request对象获取Context <\/span><\/span><\/span><\/span>ServletRequest request =<\/span> ...;<\/span> <\/span><\/span>StandardContext context =<\/span> (<\/span>StandardContext)<\/span> request.<\/span>getServletContext<\/span>();<\/span> <\/span><\/span><\/code><\/pre>步骤2：创建Filter配置<\/strong><\/p> \/\/ 定义恶意Filter <\/span><\/span><\/span><\/span>Filter evilFilter =<\/span> new<\/span> EvilFilter();<\/span> <\/span><\/span> <\/span><\/span>\/\/ 创建Filter配置 <\/span><\/span><\/span><\/span>FilterDef filterDef =<\/span> new<\/span> FilterDef();<\/span> <\/span><\/span>filterDef.<\/span>setFilterName<\/span>(<\/span>"evilFilter"<\/span>);<\/span> <\/span><\/span>filterDef.<\/span>setFilterClass<\/span>(<\/span>evilFilter.<\/span>getClass<\/span>().<\/span>getName<\/span>());<\/span> <\/span><\/span><\/code><\/pre>步骤3：配置Filter映射<\/strong><\/p> FilterMap filterMap =<\/span> new<\/span> FilterMap();<\/span> <\/span><\/span>filterMap.<\/span>setFilterName<\/span>(<\/span>"evilFilter"<\/span>);<\/span> <\/span><\/span>filterMap.<\/span>addURLPattern<\/span>(<\/span>"\/*"<\/span>);<\/span> \/\/ 拦截所有请求 <\/span><\/span><\/span><\/span>filterMap.<\/span>setDispatcher<\/span>(<\/span>DispatcherType.<\/span>REQUEST<\/span>.<\/span>name<\/span>());<\/span> <\/span><\/span><\/code><\/pre>步骤4：调整Filter顺序<\/strong><\/p> \/\/ 将恶意Filter置于链首 <\/span><\/span><\/span><\/span>context.<\/span>addFilterDef<\/span>(<\/span>filterDef);<\/span> <\/span><\/span>context.<\/span>addFilterMapBefore<\/span>(<\/span>filterMap);<\/span> <\/span><\/span><\/code><\/pre>五、防御措施<\/h2> 5.1 检测方案<\/h3> 静态检测<\/strong><\/p> 监控web.xml异常修改<\/li> 检查Filter类加载行为<\/li> <\/ul> <\/li> 动态检测<\/strong><\/p> 监控运行时Filter链变化<\/li> 检测异常URL模式注册<\/li> <\/ul> <\/li> 行为监控<\/strong><\/p> 命令执行行为检测<\/li> 异常网络连接监控<\/li> <\/ul> <\/li> <\/ol> 5.2 防护建议<\/h3> 权限控制<\/strong><\/p> 最小权限原则部署Tomcat<\/li> 严格限制管理接口访问<\/li> <\/ul> <\/li> 安全加固<\/strong><\/p> 定期更新Tomcat版本<\/li> 启用安全审计日志<\/li> <\/ul> <\/li> 运行时防护<\/strong><\/p> 使用RASP进行运行时保护<\/li> 部署WAF进行请求过滤<\/li> <\/ul> <\/li> <\/ol> 六、总结<\/h2> Tomcat Filter型内存马利用动态注册Filter的机制，通过精心构造的恶意Filter实现在内存中持久化驻留。理解Filter调用链的完整流程对于防御此类攻击至关重要。安全团队应重点关注运行时环境监控和异常行为检测，建立多层次防御体系。<\/p> 关键记忆点<\/strong>：<\/p> Filter链采用责任链模式，逐个调用<\/li> 内存马成功的关键是控制Filter在链中的位置<\/li> 防御需要结合静态检测和动态监控<\/li> 最小权限原则是基础安全保障<\/li> <\/ul> 本教学文档仅用于安全研究和技术学习，请遵守相关法律法规，勿用于非法用途。<\/em><\/p>

Tomcat Filter型内存马分析与实现教学文档<\/h1>

一、前言<\/h2>

Filter功能回顾<\/h3> Filter（过滤器）是Java Web中的核心组件，用于在请求到达Servlet之前或响应返回客户端之前进行拦截处理。通过自定义过滤器可以实现请求修改、权限验证、日志记录等功能。<\/p>

二、Tomcat Filter流程分析<\/h2>

三、Filter调用链深度分析<\/h2>

四、Filter内存马实现原理<\/h2>

五、防御措施<\/h2>

Filter功能回顾<\/h3>
Filter（过滤器）是Java Web中的核心组件，用于在请求到达Servlet之前或响应返回客户端之前进行拦截处理。通过自定义过滤器可以实现请求修改、权限验证、日志记录等功能。<\/p>