Netskope named a Leader in the 2024 Gartner® Magic Quadrant™ for Security Service Edge. Get the report

close
close
  • Why Netskope chevron

    Changing the way networking and security work together.

  • Our Customers chevron

    Netskope serves more than 3,000 customers worldwide including more than 25 of the Fortune 100

  • Our Partners chevron

    We partner with security leaders to help you secure your journey to the cloud.

Still Highest in Execution.
Still Furthest in Vision.

Learn why 2024 Gartner® Magic Quadrant™ named Netskope a Leader for Security Service Edge the third consecutive year.

Get the report
Netskope Named a Leader in the 2024 Gartner® Magic Quadrant™ for Security Service Edge graphic for menu
We help our customers to be Ready for Anything

See our customers
Woman smiling with glasses looking out window
Netskope’s partner-centric go-to-market strategy enables our partners to maximize their growth and profitability while transforming enterprise security.

Learn about Netskope Partners
Group of diverse young professionals smiling
Your Network of Tomorrow

Plan your path toward a faster, more secure, and more resilient network designed for the applications and users that you support.

Get the white paper
Your Network of Tomorrow
Introducing the Netskope One Platform

Netskope One is a cloud-native platform that offers converged security and networking services to enable your SASE and zero trust transformation.

Learn about Netskope One
Abstract with blue lighting
Embrace a Secure Access Service Edge (SASE) architecture

Netskope NewEdge is the world’s largest, highest-performing security private cloud and provides customers with unparalleled service coverage, performance and resilience.

Learn about NewEdge
NewEdge
Netskope Cloud Exchange

The Netskope Cloud Exchange (CE) provides customers with powerful integration tools to leverage investments across their security posture.

Learn about Cloud Exchange
Netskope video
The platform of the future is Netskope

Intelligent Security Service Edge (SSE), Cloud Access Security Broker (CASB), Cloud Firewall, Next Generation Secure Web Gateway (SWG), and Private Access for ZTNA built natively into a single solution to help every business on its journey to Secure Access Service Edge (SASE) architecture.

Go to Products Overview
Netskope video
Next Gen SASE Branch is hybrid — connected, secured, and automated

Netskope Next Gen SASE Branch converges Context-Aware SASE Fabric, Zero-Trust Hybrid Security, and SkopeAI-powered Cloud Orchestrator into a unified cloud offering, ushering in a fully modernized branch experience for the borderless enterprise.

Learn about Next Gen SASE Branch
People at the open space office
Designing a SASE Architecture For Dummies

Get your complimentary copy of the only guide to SASE design you’ll ever need.

Get the eBook
Make the move to market-leading cloud security services with minimal latency and high reliability.

Learn about NewEdge
Lighted highway through mountainside switchbacks
Safely enable the use of generative AI applications with application access control, real-time user coaching, and best-in-class data protection.

Learn how we secure generative AI use
Safely Enable ChatGPT and Generative AI
Zero trust solutions for SSE and SASE deployments

Learn about Zero Trust
Boat driving through open sea
Netskope achieves FedRAMP High Authorization

Choose Netskope GovCloud to accelerate your agency’s transformation.

Learn about Netskope GovCloud
Netskope GovCloud
  • Resources chevron

    Learn more about how Netskope can help you secure your journey to the cloud.

  • Blog chevron

    Learn how Netskope enables security and networking transformation through security service edge (SSE)

  • Events and Workshops chevron

    Stay ahead of the latest security trends and connect with your peers.

  • Security Defined chevron

    Everything you need to know in our cybersecurity encyclopedia.

Security Visionaries Podcast

On Patents, Trolls, and Innovation
In this episode host Emily Wearmouth chats with Suzanne Oliver, an intellectual property expert, and Krishna Narayanaswamy, co-founder and CTO of Netskope, about the world of patents.

Play the podcast
On Patents, Trolls, and Innovation
Latest Blogs

Read how Netskope can enable the Zero Trust and SASE journey through security service edge (SSE) capabilities.

Read the blog
Sunrise and cloudy sky
SASE Week 2023: Your SASE journey starts now!

Replay sessions from the fourth annual SASE Week.

Explore sessions
SASE Week 2023
What is Security Service Edge?

Explore the security side of SASE, the future of network and protection in the cloud.

Learn about Security Service Edge
Four-way roundabout
  • Company chevron

    We help you stay ahead of cloud, data, and network security challenges.

  • Leadership chevron

    Our leadership team is fiercely committed to doing everything it takes to make our customers successful.

  • Customer Solutions chevron

    We are here for you and with you every step of the way, ensuring your success with Netskope.

  • Training and Certification chevron

    Netskope training will help you become a cloud security expert.

Supporting sustainability through data security

Netskope is proud to participate in Vision 2045: an initiative aimed to raise awareness on private industry’s role in sustainability.

Find out more
Supporting Sustainability Through Data Security
Thinkers, builders, dreamers, innovators. Together, we deliver cutting-edge cloud security solutions to help our customers protect their data and people.

Meet our team
Group of hikers scaling a snowy mountain
Netskope’s talented and experienced Professional Services team provides a prescriptive approach to your successful implementation.

Learn about Professional Services
Netskope Professional Services
Secure your digital transformation journey and make the most of your cloud, web, and private applications with Netskope training.

Learn about Training and Certifications
Group of young professionals working

Malicious Office Documents: Multiple Ways to Deliver Payloads

Nov 19 2021

Co-authored by Gustavo Palazolo and Ghanashyam Satpathy

Summary

Several malware families are distributed via Microsoft Office documents infected with malicious VBA code, such as Emotet, IceID, Dridex, and BazarLoader. We have also seen many techniques employed by attackers when it comes to infected documents, such as the usage of PowerShell and WMI to evade signature-based threat detection. In this blog post, we will show three additional techniques attackers use to craft malicious Office documents.

Technique 01: VBA Code Executing Shellcode via Process Injection

The first technique involves a malicious VBA script that is used to execute a shellcode, which eventually leads to the deployment of other malware.

The VBA code is automatically executed with the “AutoOpen” feature, and from extracted macro code, we can see references to Windows APIs that are often used for process injection.

Screenshot of Windows APIs used by the VBA code.
Windows APIs used by the VBA code.

Going further, we can find a large array with integers, which are all the bytes of the shellcode.

Example of shellcode bytes within an array.
Shellcode bytes within an array.

And finally, we have the code that is responsible for executing the shellcode.

In this case, the code will be injected into “rundll32.exe” through a popular technique:

  1. A “rundll32.exe” process is created with CreateProcessA, named “RunStuff”;
  2. The code allocates a memory space in the process with VirtualAllocEx, named “AllocStuff”;
  3. The shellcode is written into the newly allocated space with WriteProcessMemory, named “WriteStuff”.
  4. Lastly, the shellcode is executed through CreateRemoteThread, named “CreateStuff”.

Once the shellcode is running, it contacts a malicious server to download the next stage, which can be any additional malware the attacker desires.

Screenshot of Shellcode executed through the infected document.
Shellcode executed through the infected document.

Technique 02: VBA Code Abusing Certutil

This one is a bit more interesting than the first one, as the malicious VBA code is using a Living-off-the-Land technique to carry out the attack.

After extracting the macro, we can see that the malware uses the “AutoOpen” feature to execute two functions, respectively “DropThyself” and “EstablishThyself”.

Screenshot of Functions executed once the document is opened.
Functions executed once the document is opened.

The first called function creates a file named “GoogleUpdater.crt” and writes a large base64 content in the certificate format.

Screenshot of Function dropping the fake certificate in the disk.
Function dropping the fake certificate in the disk.

The file is a base64 encoded executable, which is the second stage of the malware. The content is decoded through a Living-off-the-Land technique using the “certutil.exe” binary.

This is the same technique that was used by the REvil ransomware in the Kaseya attack, where the attacker claimed to have infected more than one million devices around the world.

Screenshot of Payload being decoded through “certutil.exe”
Payload being decoded through “certutil.exe”

After the second stage is decoded, the VBA function “EstablishThyself” creates a simple persistence through Windows registry.

Screenshot of Second-stage executed through simple persistence technique
Second-stage executed through simple persistence technique

In this case, the payload is an agent from a .NET Command & Control framework named Covenant. The file is packed and once running, the entry point executes a shellcode through VirtualAlloc, VirtualProtect, and CreateThread APIs.

Screenshot of Shellcode allocated and executed.
Shellcode allocated and executed.

The shellcode then unpacks the final stage.

Example of Payload being unpacked.
Payload being unpacked.

Since Covenant is developed in .NET, we can decompile the binary to extract additional information about the agent.

Screenshot of Final payload decompiled.
Final payload decompiled.

Technique 03: VBA Code Executing Shellcode via PowerShell

This technique is similar to the first one, however, the shellcode is executed through obfuscated PowerShell.

And again we see the “AutoOpen” feature of VBA Macro being used. At the beginning of the code, we see a large string being concatenated, likely to evade detection.

Screenshot of PowerShell script executed by the macro.
PowerShell script executed by the macro.

Later, the script is executed through a shell object, where the VBA code also uses concatenation in its strings:

Screenshot of PowerShell being executed by the code.
PowerShell being executed by the code.

After running the script, the macro shows a fake error message to deceive the victim.

Screenshot of VBA code displaying a fake message and exiting.
VBA code displaying a fake message and exiting.

The main PowerShell script is encoded with base64, and once we decode it, it’s possible to see APIs related to process injection and a large array of bytes, similar to the first technique.

Screenshot of PowerShell script to inject shellcode.
PowerShell script to inject shellcode.

The shellcode is also very similar to the one found in the first technique.

Screenshot of shellcode execution
Shellcode execution.

Conclusion

We have reviewed three different techniques that are being used by attackers to deliver malware through Microsoft Office documents containing malicious VBA code. It’s interesting to note that despite the differences between them, they are all abusing the “AutoOpen” function within the VBA macros to execute the malware once the document is opened and the user has enabled macros.

The above techniques demonstrate the importance of a strong security solution, as well as security training since these attack vectors can be avoided by not opening unknown attachments, or not enabling macro execution from unknown documents. Moreover, Microsoft has recommended blocking the macro execution through group policy settings by the enterprise administrator in Office 2016 onwards.

Protection

Netskope Threat Labs is actively monitoring infected documents and ensuring coverage for these types of threats.

author image
Gustavo Palazolo
Gustavo Palazolo is an expert in malware analysis, reverse engineering and security research, working many years in projects related to electronic fraud protection. He is currently working on the Netskope Research Team, discovering and analyzing new malware threats.

Stay informed!

Subscribe for the latest from the Netskope Blog