Malicious SYLK Files with MS Excel 4.0 Macros

Since about a week, we are seeing an increase of SYLK files submitted to VirusTotal. A SYLK file (SYmbolic LinK) is a pure text file format used to store Excel spreadsheets with extension .slk. Although SYLK files can't contain VBA macros, they can still contain executable code, for example DDE commands or MS Excel 4.0 … Continue reading Malicious SYLK Files with MS Excel 4.0 Macros

Differential Malware Analysis: An Example

There are many ways to analyze malware. In this blog post, we illustrate a typical analysis method: comparing an unknown sample with a known sample, to determine if the unknown sample is malicious or not. During one of our engagements, we came across a PDF document that triggered our anti-virus. What intrigued us, was that … Continue reading Differential Malware Analysis: An Example

PowerShell Inside a Certificate? – Part 3

In the first part of this series, we explained the internal structure of certificates and how this knowledge can help us detect fake certificates. In this part, we will provide different rules that you can use in your organization to detect these certificates. YARA This is the YARA rule that started this research: This YARA … Continue reading PowerShell Inside a Certificate? – Part 3

PowerShell Inside a Certificate? – Part 2

In our previous blogpost, we developed a method to detect certificate files that do not contain a real certificate. Trojanized certificates like these are often not detected by AV and IDS. Although we found all kinds of payloads, fake certificates containing a Windows executable appear to be the most common. In this post we will … Continue reading PowerShell Inside a Certificate? – Part 2

PowerShell Inside a Certificate? – Part 1

With the help of a specifically crafted YARA rule developed by NVISO analysts, we found multiple certificate files (.crt) that do not contain a certificate, but instead a malicious PowerShell script. In this blog post, we explain how we crafted this YARA rule. Certificates Certificate files in Windows can have different extensions, like .cer and … Continue reading PowerShell Inside a Certificate? – Part 1

Shortcomings of blacklisting in Adobe Reader and what you can do about it

A variation of a class of malicious PDFs appeared in the wild. In this blog post, we will show you how to protect your systems and how to analyze these PDFs. The PDFs embed a file type with extension .SettingContent-ms that can be used on Windows 10 to execute arbitrary code. We have observed on … Continue reading Shortcomings of blacklisting in Adobe Reader and what you can do about it

Extracting a Windows Zero-Day from an Adobe Reader Zero-Day PDF

In May 2018, when ESET published a blog post covering PDFs with 2 zero days, our interest was immediately piqued. Promptly after our analysis of these PDFs, we send out an early warning to our customers. Now that Microsoft published a blog post with the detailed analysis of the zero days, we find it appropriate … Continue reading Extracting a Windows Zero-Day from an Adobe Reader Zero-Day PDF

Painless Cuckoo Sandbox Installation

TLDR: As part of our SANS SEC599 development efforts, we updated (fixed + added some new features) an existing Cuckoo Auto Install script by Buguroo Security to automate Cuckoo sandbox installation (& VM import). Download it from our Github here. Intro As a blue team member, you often have a need to analyze a piece … Continue reading Painless Cuckoo Sandbox Installation

Creating custom YARA rules

In a previous post, we created YARA rules to detect compromised CCleaner executables (YARA rules to detect compromised CCleaner executables). We will use this example as an opportunity to illustrate how the creation of these custom YARA rules was performed. In its blog post, Talos shared 3 hashes as Indicators Of Compromise (IOCs): 1a4a5123d7b2c534cb3e3168f7032cf9ebf38b9a2a97226d0fdb7933cf6030ff 6f7840c77f99049d788155c1351e1560b62b8ad18ad0e9adda8218b9f432f0a9 … Continue reading Creating custom YARA rules

Going beyond Wireshark: experiments in visualising network traffic

Introduction At NVISO Labs, we are constantly trying to find better ways of understanding the data our analysts are looking at. This ranges from our SOC analysts looking at millions of collected data points per day all the way to the malware analyst tearing apart a malware sample and trying to make sense of its … Continue reading Going beyond Wireshark: experiments in visualising network traffic