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.

TL;DR
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.

TL;DR
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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Old school: evil Excel 4.0 macros (XLM)

In this post, I will dive into Excel 4.0 macros (also called XLM macros – not XML) for offensive purposes. If you grew up in the Windows 95 age or later, just as I did, you might have never heard of this technology that was introduced as early as 1992. Virtually all malicious macro documents for MS Office are based on Visual Basic for Applications (VBA). However, XLM macros are a hidden gem for red teamers and turn out to be a very good alternative to VBA macros for offensive purposes: XLM can be difficult to analyse and it appears that most antivirus solutions have trouble detecting XLM maldocs. And although the technology is 26 years old by now, Excel 4.0 macros are still supported in the most recent Microsoft Office versions (including Office 2016, at time of writing).

This blog post is a teaser for the presentation by Pieter Ceelen and Stan Hegt titled “The MS Office magic show” at DerbyCon 2018 (Sunday, 1 PM). After the presentation, the video and slide material will be published online.

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HTML smuggling explained

Using a combination of HTML5 and JavaScript to sneak malicious files past content filters is not a new offensive technique. This mechanism has been incorporated into popular offensive frameworks such as Demiguise and SharpShooter for example. However, from our discussions and trainings with blue teams, we have learned that many defenders are not aware of this technique or its implications. In this blog post, we will explain how a few lines of JavaScript have big impact on perimeter security.

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