Quantify the value of Netskope One SSE – Get the 2024 Forrester Total Economic Impact™ study

close
close
  • Why Netskope chevron

    Changing the way networking and security work together.

  • Our Customers chevron

    Netskope serves more than 3,400 customers worldwide including more than 30 of the Fortune 100

  • Our Partners chevron

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

A Leader in SSE. Now a Leader in Single-Vendor SASE.

Learn why Netskope debuted as a leader in the 2024 Gartner® Magic Quadrant™️ for Single-Vendor Secure Access Service Edge

Get the report
Customer Visionary Spotlights

Read how innovative customers are successfully navigating today’s changing networking & security landscape through the Netskope One platform.

Get the eBook
Customer Visionary Spotlights
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
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
Aerial view of a city
  • Security Service Edge chevron

    Protect against advanced and cloud-enabled threats and safeguard data across all vectors.

  • SD-WAN chevron

    Confidently provide secure, high-performance access to every remote user, device, site, and cloud.

  • Secure Access Service Edge chevron

    Netskope One SASE provides a cloud-native, fully-converged and single-vendor SASE solution.

The platform of the future is Netskope

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
SASE Architecture For Dummies

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

Get the eBook
SASE Architecture For Dummies 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 secure access service edge (SASE)

  • 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

2025 Predictions
In this episode of Security Visionaries, we're joined by Kiersten Todt, President at Wondros and former Chief of Staff for the Cybersecurity and Infrastructure Security Agency (CISA) to discuss predictions for 2025 and beyond.

Play the podcast Browse all podcasts
2025 Predictions
Latest Blogs

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

Read the blog
Sunrise and cloudy sky
SASE Week 2024 On-Demand

Learn how to navigate the latest advancements in SASE and zero trust and explore how these frameworks are adapting to address cybersecurity and infrastructure challenges

Explore sessions
SASE Week 2024
What is SASE?

Learn about the future convergence of networking and security tools in today’s cloud dominant business model.

Learn about SASE
  • Company chevron

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

  • Careers chevron

    Join Netskope's 3,000+ amazing team members building the industry’s leading cloud-native security platform.

  • Customer Solutions chevron

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

  • Training and Accreditations 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
Help shape the future of cloud security

At Netskope, founders and leaders work shoulder-to-shoulder with their colleagues, even the most renowned experts check their egos at the door, and the best ideas win.

Join the team
Careers at Netskope
Netskope dedicated service and support professionals will ensure you successful deploy and experience the full value of our platform.

Go to Customer Solutions
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

Not Laughing: Malicious Office Documents using LoLBins

Jun 29 2021

Co-authored by Ghanashyam Satpathy and Jenko Hwong

Summary

Attackers have long used phishing emails with malicious Microsoft Office documents, often hosted in popular cloud apps like Box and Amazon S3 to increase the chances of a successful lure. The techniques being used with Office documents are continuing to evolve.

In August – September of 2020, we analyzed samples that used advanced techniques like:

  1. Constructing a PowerShell script at runtime. 
  2. Constructing WMI namespaces at runtime. 
  3. Using VBA logic obfuscation to evade static and signature-based detections.

In January 2021, we examined samples that use obfuscation and embedded XSL scripts to download payloads.

In this blog post, we will examine a new set of malicious Office documents using additional techniques to evade signature-based threat detection, including:

  1. Embedded base64 payloads 
  2. Code injection

This is the first time we have seen attackers using Office documents that use both VBA and LoLbins (certutil.exe and mavinject.exe). This blog post provides a default teardown of how these techniques are being used by the Lazarus Group. 

Analysis

In this blog post, we examine a malicious Microsoft Word document linked to the Lazarus Group:

MD5

648dea285e282467c78ac184ad98fd77

SHA-1

5c194ec7cfe33dd738fca71adf960c85e6ed7646

SHA-256

8e1746829851d28c555c143ce62283bc011bbd2acfa60909566339118c9c5c97 

The techniques used in the sample include:

  • Embedded payload in base64
  • Decoding the base64 payload using certutil.exe
  • Using mavinject.exe for code injection

Mavinject.ext and certutil.exe are Windows LoLbins (living off the land binaries), used by this sample to connect to the C&C servers and download next stage payloads.

Embedded base64 payload

The sample is a Word document (screenshot below) that prompts the user to click the “Enable Content” button. The macro code has an auto-trigger routine to execute as soon as “Enable Content” is clicked.

Screenshot of sample Word doc

The initial payload is stored inside the VBA code as a base64 encoded string. The base64 string is saved into a file on the local disk and later decoded back into a PE file. For decoding it uses certutil.exe, a Windows utility installed as part of Certificate Services that is used to configure Certificate Services, backup and restore CA components, and verify certificates and key pairs. The VBA code references certutil.exe using a wildcard string (certut*) inside the VBA code. The use of a wildcard is to evade simple pattern match on certutil.exe. The VBA script invokes certutil.exe with the -decode command line option to decode the base64 encoded data. 

The following screenshot shows the VBA project. The base64 string can be seen inside the VBA code. The VBA Function WLQGQifZzoSMZHc is invoked inside Document_Open():

Screenshot showing the VBA project with the base64 string in the VBA code.

The sample writes the base64 content into a file at location C:\Drivers and names it: DriverGFC.tmp. It then copies certutil.exe from system location to c:\Drivers location and renames it as DriverUpdateRx.exe. It refers to certutil using a wildcard as certut*.exe while copying it from the system location. This is done to evade signatures that key off of the string “certutil.” The original payload is renamed to DriverCLHD.tmp. The command executed at runtime is shown below:

"C:\Windows\System32\cmd.exe" /c copy /b C:\Windows\system32\certut*.exe c:\Drivers\DriverUpdateRx.exe

"C:\Windows\System32\cmd.exe" /c copy /b c:\Drivers\DriverGFC.tmp+c:\Drivers\DriverGFXCoin.tmp c:\Drivers\DriverCLHD.tmp & del c:\Drivers\DriverGFC.tmp & del c:\Drivers\DriverGFXCoin.tmp

It decodes the file content using certutil (now copied to  DriverUpdateRx.exe) with the -decode option. 

This creates the output file DriverGFY.db. After decoding, the sample deletes the DriverUpdateRx.exe from C:\Drivers location and creates another copy of DriverGFY.db as DriverGFY.db.dll. The technique the attacker is using here is Deobfuscate/Decode Files or Information from the Mitre ATT&CK Framework.

The command executed at runtime is shown below:

"C:\Windows\System32\cmd.exe" /c c:\Drivers\DriverUpdateRx.exe -decode c:\Drivers\DriverCLHD.tmp c:\Drivers\DriverGFY.db & del c:\Drivers\DriverCLHD.tmp & del c:\Drivers\DriverUpdateRx.exe

"C:\Windows\System32\cmd.exe" /c copy /b c:\Drivers\DriverGFY.db c:\Drivers\DriverGFY.db.dll

Using the WMI utility, it gets the handle to the running instance of Explorer.exe. Following is the VBA code snippet:

Set vQSppIeZ = GetObject("winmgmts:\\.\root\cimv2")
Set HfXHePNP = vQSppIeZ.ExecQuery("Select * from Win32_Process where name='explorer.exe'")

Using mavinject.exe (Microsoft Application Virtualization Injector), it does code injection into explorer.exe with its payload DriverGFY.db. The technique the attacker is using here is Process Injection in the Mitre ATT&CK Framework.

The command executed at runtime for doing code injection is shown below:

"C:\Windows\System32\cmd.exe" /c mavinject.exe 568 /injectrunning c:\Drivers\DriverGFY.db

The following is a screenshot of the HexEdit view of the payload after it has been decoded using certutil.exe:

Screenshot of the HexEdit view of the payload after it has been decoded using certutil.exe

The SysMon capture of Process Injection into Explorer.exe is:

Screenshot of the SysMon capture of Process Injection into Explorer.exe.

The screenshot of payload code shows a reference to download the next stage payload. The Exported function InitUpdate downloads from allgraphicart[.]com.

Screenshot of payload code showing a reference to download the next stage payload.

Netskope Detection

At Netskope, we apply a hybrid approach to malicious Office document detection that leverages a combination of heuristics and supervised machine learning to identify malicious code embedded in documents. Netskope Advanced Threat Protection provides proactive coverage against zero-day samples including APT and other malicious Office documents using both our ML and heuristic-based static analysis engines, as well as our cloud sandbox. The following screenshot shows the detection for 648DEA285E282467C78AC184AD98FD77, indicating it was detected by both Netskope AV and the Netskope Advanced Heuristic Engine. The indicators section shows the reasons it was detected as malicious: the sample auto executes the macro code described in this blog post, writes files to the system, and executes system APIs.

Conclusion

In addition to the techniques covered in our previous blog posts, the sample we analyzed in this post uses two additional techniques that leverage LoLBins:

  1. Using certutil.exe to decode an enclosed base64 payload to PE file. 
  2. Using mavinject.exe to inject the payload into explorer.exe.

Netskope Advanced Threat Protection includes a custom Microsoft Office file analyzer and a sandbox to detect campaigns like APT that are in active development and are using new Office documents to spread. We will continue to provide updates on this threat as it evolves.

IOCs

Sample 1: 648DEA285E282467C78AC184AD98FD77 

Dropped executable file 

C:\Drivers\DriverGFY.db

DNS requests

domain allgraphicart[.]com

Connections  

ip 155.138.135[.]1

ip 184.24.77[.]69


Thank you to Zhi Xu and Benjamin Chang for helping analyze the sample files and contributing to this blog. 

author image
Ghanashyam Satpathy
Ghanashyam is a Principal Researcher with the Netskope Efficacy team. His background is building threat detection products using AI/ML technology.
Ghanashyam is a Principal Researcher with the Netskope Efficacy team. His background is building threat detection products using AI/ML technology.

Stay informed!

Subscribe for the latest from the Netskope Blog