Abusing the SYLK file format

This blog is about the SYLK file format, a file format from the 1980s that is still supported by the most recent MS Office versions. As it turns out, this file format is a very good candidate for creating weaponized documents that can be used by attackers to establish an initial foothold. In our presentation at DerbyCon 8 we already demonstrated some of the powers of SYLK.

In this blog post we will dive into additional details of this file format. We also provide recommendations for mitigations against weaponized SYLK files.

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Red Team Tactics: Active Directory Recon using ADSI and Reflective DLLs

In this blog post we will explain how you can enumerate Active Directory from Cobalt Strike using the Active Directory Service Interfaces (ADSI) in combination with C/C++. This may help staying under the radar in environments where PowerShell and .NET are heavily monitored.

Imagine you are in a TIBER, CBEST or other long-term red team assessment and finally managed to get a foothold into the target’s network. Many hours of preparation finally pay off and your payload plus C2 channel bypass the target’s security measures. How can you run your tools for the next steps in your attack (such as Active Directory reconnaissance), without triggering modern defenses on the compromised host such as AMSI or script block logging?

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Red Team Tactics: Combining Direct System Calls and sRDI to bypass AV/EDR

In this blog post we will explore the use of direct system calls, restore hooked API calls and ultimately combine this with a shellcode injection technique called sRDI. We will combine these techniques in proof of concept code which can be used to create a LSASS memory dump using Cobalt Strike, while not touching disk and evading AV/EDR monitored user-mode API calls.

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Evil Clippy: MS Office maldoc assistant

At BlackHat Asia we released Evil Clippy, a tool which assists red teamers and security testers in creating malicious MS Office documents. Amongst others, Evil Clippy can hide VBA macros, stomp VBA code (via p-code) and confuse popular macro analysis tools. It runs on Linux, OSX and Windows.

In this blog post we will explore the features of Evil Clippy and the technology behind it. The latest source code of the tool can be found here:


Latest binary releases are available at:


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Introducing RedELK – Part 1: why we need it

This multi-part blog post is about a tool we released: RedELK. In a few words you can describe it as a “Red Team’s SIEM”, although it actually does a few more things to ease the life of red teams. We released it right after our talk at BruCON 2018, and you may have already seen it at our GitHub. But until now we haven’t had the time to articulate our reasoning and give it a proper introduction.

This first part covers our reasoning. A the second part (soon to be released) we’ll dive into the technical details, explain basic usage and show you how you can benefit from using it as a red teamer.

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Recordings of our DerbyCon and BruCON presentations

This month (October 2018) our team members presented at two hacker conferences:

  • The MS Office magic show at DerbyCon
  • Mirror on the wall: using blue team techniques in red team ops at BruCON

Below, you can find the video recordings of these presentations.

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Building resilient C2 infrastructures using DNS over HTTPS (DoH)

Persistent access to a target’s network is one of the milestones in any offensive operation. During our operations, we use various types of short-haul beacons for day-to-day operations. If all short-haul beacons fail, a long-haul beacon which calls back much less frequently, can restore access to the target’s network. As such, a long-haul beacon should function in a way that it does not attract the attention of the blue team.

For OPSEC reasons, it is a good habit to split your command and control (C2) between low-and-slow channels (stage 1, long-haul) and operational channels (stage 2, short-haul). This blog post provides operational details for building a stage 1 C2 channel using DNS over HTTPS (HTTPS calls to dns.google.com to retrieve DNS TXT records) to trigger the download of a stager that will subsequently launch a payload for stage 2 C2.

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Sylk + XLM = Code execution on Office 2011 for Mac

At our Derbycon talk, the MS Office Magic Show, Stan and myself presented various novel techniques for abusing Excel and Word in Red Teaming operations. One of the tricks introduced was about the Sylk fileformat and Excel 4.0 / XLM macro’s. Full detailled blogs on Sylk and other discussed subjects will follow later. For now it suffices to say that we shared a 99byte Sylk file that pops Calc using XLM when the victim enables macro. As Sylk files are text files they do not open in protected mode.

In Office 2011 for Mac XLM Macro’s in Sylk files are auto executed (no protected mode or macro prompt). Time to say goodbye and really remove office 2011. Issue may even be triggered if you have both Office 2016 and 2011 for Mac installed.

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