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A phishing document signed by Microsoft – part 2

This is the second part of our blog series in which we walk you through the steps of finding and weaponising other vulnerabilities in Microsoft signed add-ins. Our previous post described how a Microsoft-signed Analysis Toolpak Excel add-in (.XLAM) was vulnerable to code hijacking by loading an attacker controlled XLL via abuse of the RegisterXLL function.

In this post we will dive deep into a second code injection vulnerability in the Analysis Toolpak in relation to the use of the ExecuteExcel4Macro function in a Microsoft-signed Excel add-in. Furthermore, we will show that the Solver add-in is vulnerable to a similar weaknesses with yet another vector. In particular, we will discuss:

  • Walkthrough of the Analysis Toolpak code injection vulnerability patched by CVE-2021-28449
  • Exploitation gadgets for practical weaponisation of such a vulnerability
  • Weakness in Solver Add-in
  • Our analysis of Microsoft’s patch

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A phishing document signed by Microsoft – part 1

This blog post is part of series of two posts that describe weaknesses in Microsoft Excel that could be leveraged to create malicious phishing documents signed by Microsoft that load arbitrary code.

These weaknesses have been addressed by Microsoft in the following patch: CVE-2021-28449. This patch means that the methods described in this post are no longer applicable to an up-to-date and securely configured MS Office install. However, we will uncover a largely unexplored attack surface of MS Office for further offensive research and will demonstrate practical tradecraft for exploitation.

In this blog post (part 1), we will discuss the following:

  • The Microsoft Analysis ToolPak Excel and vulnerabilities in XLAM add-ins which are distributed as part of this.
  • Practical offensive MS Office tradecraft which is useful for weaponizing signed add-ins which contain vulnerabilities,

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Our reasoning for Outflank Security Tooling

TLDR: We open up our internal toolkit commercially to other red teams. This post explains why.

Is blue catching your offensive actions? Are you relying on public or even commercial tools, but are these flagged by AV and EDR? Hesitant on investing deeply in offensive research and development? We’ve been there. But several years ago, we made the switch and started heavily investing in research. Our custom toolset was born.

Today we open up our toolset to other red teams in a new service called Outflank Security Tooling, abbreviated OST. We are super(!) excited about this. We truly think this commercial model is a win-win and will help other red teams and subsequently many organisations worldwide. You can find all the details at the product page. But there is more to be explained about why we do this,

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Catching red teams with honeypots part 1: local recon

This post is the first part of a series in which we will cover the concept of using honeypots in a Windows environment as an easy and cost-effective way to detect attacker (or red team) activities. Of course this blog post is about catching real attackers, not just red teams. But we picked this catchy title as the content is based on our red teaming experiences.

Upon mentioning honeypots, a lot of people still think about a system in the network hosting a vulnerable or weakly configured service. However, there is so much more you can do, instead of spawning a system. Think broad: honey files, honey registry keys, honey tokens, honey (domain) accounts or groups, etc.

In this post, we will cover:

  • The characteristics of an effective honeypot.
  • Walkthrough on configuring a file- and registry based honeypots using audit logging and SACLs.

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Direct Syscalls in Beacon Object Files

In this post we will explore the use of direct system calls within Cobalt Strike Beacon Object Files (BOF). In detail, we will:

  • Explain how direct system calls can be used in Cobalt Strike BOF to circumvent typical AV and EDR detections.
  • Release InlineWhispers: a script to make working with direct system calls more easy in BOF code.
  • Provide Proof-of-Concept BOF code which can be used to enable WDigest credential caching and circumvent Credential Guard by patching LSASS process memory.

Source code of the PoC can be found here:

https://github.com/outflanknl/WdToggle

Source code of InlineWhispers can be found here:

https://github.com/outflanknl/InlineWhispers

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RedELK Part 3 – Achieving operational oversight

This is part 3 of a multipart blog series on RedELK: Outflank’s open sourced tooling that acts as a red team’s SIEM and helps with overall improved oversight during red team operations.

In part 1 of this blog series I discussed the core concepts of RedELK and why you should want a tool like this. In part 2 I described a walk-through on integrating RedELK into your red teaming infrastructure. Read those blogs to get a better background understanding of RedELK.

For this blog I’ve setup and compromised a fictitious company. I use the logs from that hack to walk through various options of RedELK. It should make clear why RedELK is really helpful in gaining operational oversight during the campaign.

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Mark-of-the-Web from a red team’s perspective

Zone Identifier Alternate Data Stream information, commonly referred to as Mark-of-the-Web (abbreviated MOTW), can be a significant hurdle for red teamers and penetration testers, especially when attempting to gain an initial foothold.

Your payload in the format of an executable, MS Office file or CHM file is likely to receive extra scrutiny from the Windows OS and security products when that file is marked as downloaded from the internet. In this blog post we will explain how this mechanism works and we will explore offensive techniques that can help evade or get rid of MOTW.

Note that the techniques described in this blog post are not new. We have witnessed all of them being abused in the wild. Hence, this blog post serves to raise awareness on these techniques for both red teamers (for more realistic adversary simulations) and blue teamers (for better countermeasures and understanding of attacker techniques).

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Red Team Tactics: Advanced process monitoring techniques in offensive operations

In this blog post we are going to explore the power of well-known process monitoring utilities and demonstrate how the technology behind these tools can be used by Red Teams within offensive operations.

Having a good technical understanding of the systems we land on during an engagement is a key condition for deciding what is going to be the next step within an operation. Collecting and analysing data of running processes from compromised systems gives us a wealth of information and helps us to better understand how the IT landscape from a target organisation is setup. Moreover, periodically polling process data allows us to react on changes within the environment or provide triggers when an investigation is taking place.

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RedELK Part 2 – getting you up and running

This is part 2 of a multipart blog series on RedELK: Outflank’s open sourced tooling that acts as a red team’s SIEM and also helps with overall improved oversight during red team operations.

In part 1 of this blog series I have discussed the core concepts of RedELK and why you should want something like this. In this blog post I will walk you through integrating RedELK into your red teaming infrastructure. In future parts I will explain the core functionality of RedELK, and on the alarming of detection by blue teams.

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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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