Here is my writeup about CVE-2020-1170, an elevation of privilege bug in Windows Defender. Finding a vulnerability in a security-oriented product is quite satisfying. Though, there was nothing groundbreaking. It’s quite the opposite actually and I’m surprised nobody else reported it before me.

This is a kind of follow-up to my last post, in which I discussed a technique that can be used for elevating privileges to SYSTEM when you have impersonation capabilities. In the last part, I explained how this type of vulnerability could be fixed and I even illustrated it with a concrete example of a workaround that was implemented by Microsoft 10 years ago in the context of the Service Tracing feature. Though, I also insinuated that this security measure could be bypassed. So, let’s see how we can make a 10-year old vulnerability great again…

Over the last few years, tools such as RottenPotato, RottenPotatoNG or Juicy Potato have made the exploitation of impersonation privileges on Windows very popular among the offensive security community. Though, recent changes to the operating system have intentionally or unintentionally reduced the power of these techniques on Windows 10 and Server 2016/2019. Today, I want to introduce a new tool that will allow pentesters to easily leverage these privileges again.

Whenever a “new” DLL hijacking / planting trick is posted on Twitter, it generates a lot of comments. “It’s not a vulnerability!” or “There is a lot of hijackable DLLs on Windows…” are the most common reactions. Though, people often don’t really speak about the same thing, hence the overall confusion which leads us nowhere. I don’t pretend to know the ultimate truth but I felt the need to write this post in order to hopefully clarify some points.

What if I told you that all editions of Windows Server, from 2008R2 to 2019, are prone to a DLL Hijacking in the %PATH% directories? What if I also told you that the impacted service runs as NT AUTHORITY\SYSTEM and that the DLL loading can be triggered by a normal user, on demand, and without the need of a machine reboot? Provided that you found some %PATH% directories configured with weak permissions, this would probably be the most straightforward privilege escalation technique I know. I don’t know why there hasn’t been any publication about this yet. Anyway, I’ll try to fill this gap.

Although this vulnerability doesn’t directly result in a full elevation of privileges with code execution as NT AUTHORITY\SYSTEM, it is still quite interesting because of the exploitation “tricks” involved. Diagnostic Tracking Service (a.k.a. Connected User Experiences and Telemetry Service) is probably one of the most controversial Windows features, known for collecting user and system data. Therefore, the fact that I found an Information Disclosure vulnerability in this service is somewhat ironic. The bug allowed a local user to read arbitrary files in the context of NT AUTHORITY\SYSTEM.

This post is about an arbitrary file move vulnerability I found in the Background Intelligent Transfer Service. This is yet another example of a privileged file operation abuse in Windows 10. There is nothing really new but the bug itself is quite interesting because it was hidden in an undocumented function. Therefore, I will explain how I found it and I will also share some insights about the reverse engineering process I went through in order to identify the logic flaw. I hope you’ll enjoy reading it as much as I enjoyed writing it.

In this post, I’ll discuss an arbitrary file move vulnerability I found in Windows Service Tracing. From my testing, it affected all versions of Windows from Vista to 10 but it’s probably even older because this feature was already present in XP.

A DLL hijacking “vulnerability” in the CDPSvc service was reported to Microsoft at least two times this year. As per their policy though, DLL planting issues that fall into the category of PATH directories DLL planting are treated as won’t fix , which means that it won’t be addressed (at least in the near future). This case is very similar to the IKEEXT one in Windows Vista/7/8. The big difference is that CDPSvc runs as LOCAL SERVICE instead of SYSTEM so getting higher privileges requires an extra step.

I want to tell you the story of a service account which lost all its powers (a.k.a. privileges). Windows world is getting increasingly ruthless and when the system considers you are not worthy, this is what happens. Fortunately for our service account, all is not lost, there’s still hope. In this merciless world, you can always turn to the old sages to find some comfort and support. Among them, the Task Scheduler might be willing to help and restore what was lost, provided that you ask kindly…

In the previous post, I showed how the USO client could be used to interact with the USO service and thus have it load the windowscoredeviceinfo.dll DLL on demand with the StartScan option. I wasn’t totally satisfied with this though. So, I reverse engineered a part of the client and the server in order to replicate its behavior as a standalone project that could be reused in future exploits. This is what I’ll try to show and explain in this second part.

The DiagHub DLL loading technique found by James Forshaw (a.k.a. @tiraniddo) has become very famous. Whenever you found an arbitrary file write as SYSTEM in Windows or in some third-party software, you could use this trick to get code execution on demand, and without rebooting. Unfortunately (or fortunately depending on your point of view), this method was mitigated by Microsoft in Windows 10 build 1903. Andrea Pierini (aka @decoder_it) mentionned this briefly on Twitter. Here, I want to share an alternative method I found while looking for DLL hijacking weaknesses on the most recent version of Windows.

DLL Hijacking is the first Windows privilege escalation technique I worked on as a junior pentester, with the IKEEXT service on Windows 7 (or Windows Server 2008 R2). Here, I’d like to discuss one of its variants - DLL Proxying - and provide a step-by-step guide for easily crafting a custom DLL wrapper in the context of a privilege escalation.

In the previous part, I discussed the method used by Didier Stevens to run cmd.exe within Excel (or Word) thanks to a custom shellcode in VBA. I also outlined its limitations. In this part, I’ll try to explain how I was able to address them in order to provide a more versatile method that pentesters can easily reuse when required. The code can be found here.

In this post, I’d like to share a technique that I often use to break out of highly constrained desktop environments such as CItrix. The only prerequisite is to have access to Microsoft Word or Excel with the VBA editor enabled.

A vulnerability was discovered in the uxdqmsrv binary. It consists in an arbitrary file write as root that can be leveraged by any local user to gain full root privileges on the host (UNIX/Linux only).

Indeed, the program tries to write to a log file that can be specified using the U_LOG_FILE environment variable. When uxdqmsrv is owned by root and the SUID bit is set (default setup), this file will be created with root privileges if it doesn’t exist. Using a UNIX/Linux feature called umask, a local user can also control the permissions of the created file and make it world-writable, thus controlling the content of the file.

A vulnerability was discovered in the mcmnm binary. It is compiled with a RPATH starting with .:. Therefore, any user can craft a malicious library (e.g.: libmcmclnx.so) and then run mcmnm from the same directory to execute code as root.