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:

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:

Above you can see the server requires two options:

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

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

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:

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:

Like this!

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

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:

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).