Clément Labro – SCRT Team Blog

From a Regular Red Team Exercise to Developing a Custom C2 Channel over MS Teams

It’s early June 2025, we are preparing our C2 infrastructure and payload for an upcoming red team engagement. We know the client, we also know some aspects of their infrastructure because we do a lot of regular pentests for them throughout the year. We don’t need to worry about the social engineering part because it was agreed to do the tests in an “assume breach” scenario and we’ll thus have a contact on site who will download, open or execute whatever we ask them to. So, the objective is simple, we have approximately 2 months to get an initial foothold on the network and do some post-exploitation.

We can’t say that we felt highly confident, but we had a comfortable margin for error, and we knew that we could go back to the drawing board in case something did not work as intended. Little did we know that we had greatly underestimated the difficulty of the task, and that a key part of their infrastructure would end up completely ruining our plans. We were not quite prepared for what lied ahead of us.

Hijacking the Windows “MareBackup” Scheduled Task for Privilege Escalation

The built-in “MareBackup” scheduled task is susceptible to a trivial executable search order hijacking, which can be abused by a low-privileged user to gain SYSTEM privileges whenever a vulnerable folder is prepended to the system’s PATH environment variable (instead of being appended).

Reinventing PowerShell in C/C++

I like PowerShell, I like it a lot! I like its versatility, its ease of use, its integration with the Windows operating system, but it also has a few features, such as AMSI, CLM, and other logging capabilities, that slow it down. You know, I’m thinking about the performance gain here. I believe my scripts could run a lot faster without them.

Jokes aside, I know that a lot has already been done around this subject, but I wanted to approach the problem in a slightly different way than the existing projects. So, I worked on a way to instantiate a full-blown PowerShell console using only native code, which allowed me to do some “cleaning” at the same time.

Exploiting KsecDD through Server Silos

Earlier this year, an intriguing admin-to-kernel technique was published by @floesen_ in the form of a proof-of-concept (PoC) on GitHub. The author mentioned a strong limitation involving LSASS and Server Silos, without providing much details about it. This piqued our interest, so we decided to give it a second look…

Ghost in the PPL Part 3: LSASS Memory Dump

Following my failed attempt to achieve arbitrary code execution within a protected LSASS process using the BYOVDLL technique and an N-day exploit in the KeyIso service, I took a step back, and ~~reconsidered my life choices~~ opted for a less ambitious solution: a (not so) simple memory dump. After all, when it comes to LSASS, we are mostly interested in extracting credentials stored in memory.

Ghost in the PPL Part 2: From BYOVDLL to Arbitrary Code Execution in LSASS

In the previous part, I showed how a technique called “Bring Your Own Vulnerable DLL” (BYOVDLL) could be used to reintroduce known vulnerabilities in LSASS, even when it’s protected. In this second part, I’m going to discuss the strategies I considered and explored to improve my proof-of-concept, and hopefully achieve arbitrary code execution.

Ghost in the PPL Part 1: BYOVDLL

In this series of blog posts, I will explore yet another avenue for bypassing LSA Protection in Userland. I will also detail the biggest challenges I faced while developing a proof-of-concept, and discuss some novel techniques and tricks to load an arbitrary DLL in LSASS, or even dump its memory.

A Deep Dive into TPM-based BitLocker Drive Encryption

When I investigated CVE-2022-41099, a BitLocker Drive Encryption bypass through the Windows Recovery Environment (WinRE), the fact that the latter was able to transparently access an encrypted drive without requiring the recovery password struck me. My initial thought was that there had to be a way to reproduce this behavior and obtain the master key from the Recovery Environment (WinRE). The outcome of a generic BitLocker bypass was too tempting not to explore this idea…

CVE-2022-41099 – Analysis of a BitLocker Drive Encryption Bypass

In November 2022, an advisory was published by Microsoft about a BitLocker bypass. This vulnerability caught my attention because the fix required a manual operation by users and system administrators, even after installing all the security updates. Couple this with the fact that the procedure was not well documented initially, and you have the perfect recipe for disaster.

This is typically the kind of vulnerability you do not want to deal with when you are in charge of a large fleet of workstations and laptops. However, on the other side of things, hard to patch vulnerabilities such as this one usually offer the best opportunities for red teamers and the like. This is where my journey investigating this bug and learning more about TPM-based BitLocker Drive Encryption began.

Bypassing PPL in Userland (again)

This post is a sequel to Bypassing LSA Protection in Userland and The End of PPLdump. Here, I will discuss how I was able to bypass the latest mitigation implemented by Microsoft and develop a new Userland exploit for injecting arbitrary code in a PPL with the highest signer type.