SASE Week 2023 On-Demand! Explore sessions.

  • Security Service Edge Products

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

  • Borderless SD-WAN

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

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
Borderless SD-WAN: Ushering in the New Era of Borderless Enterprise

Netskope Borderless SD-WAN offers an architecture that converges zero trust principles and assured application performance to provide unprecedented secure, high-performance connectivity for every site, cloud, remote user, and IoT device.

Read the article
Borderless SD-WAN
  • NewEdge

    NewEdge is the world’s largest, highest-performing security private cloud.

  • Cloud Security Platform

    Unrivaled visibility and real-time data and threat protection on the world's largest security private cloud.

  • Technology Partners & Integrations

    Netskope partners with the strongest companies in enterprise technology.

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
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
Netskope video
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 enables a safe, cloud-smart, and fast journey to adopt cloud services, apps, and public cloud infrastructure.

Learn about Industry Solutions
Wind turbines along cliffside
  • Resources

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

  • Blog

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

  • Events & Workshops

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

  • Security Defined

    Everything you need to know in our cybersecurity encyclopedia.

Security Visionaries Podcast

Unveiling the Under-reported Aspects of AI
Emily Wearmouth sits down with Neil Thacker, EMEA CISO, Yihua Liao, Head of Netskope AI Labs, and Suzanne Oliver, Director of IP Strategy at Scintilla, to discuss the topics in the realm of AI that they each wish people were discussing more.

Play the podcast
Unveiling the Under-reported Aspects of AI Social card
Latest Blogs

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
  • Our Customers

    Netskope serves more than 2,000 customers worldwide including more than 25 of the Fortune 100

  • Customer Solutions

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

  • Netskope Community

    Learn from other network, data, and security professionals.

  • Training and Certification

    Netskope training will help you become a cloud security expert.

We help our customers to be Ready for Anything

See our Customers
Woman smiling with glasses looking out window
Netskope’s talented and experienced Professional Services team provides a prescriptive approach to your successful implementation.

Learn about Professional Services
Netskope Professional Services
The Netskope Community can help you and your team get more value out of products and practices.

Go to the Netskope Community
The Netskope Community
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
  • Company

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

  • Why Netskope

    Cloud transformation and work from anywhere have changed how security needs to work.

  • Leadership

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

  • Partners

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

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
Highest in Execution. Furthest in Vision.

Netskope recognized as a Leader in the 2023 Gartner® Magic Quadrant™ for Security Service Edge.

Get the report
Netskope recognized as a Leader in the 2023 Gartner® Magic Quadrant™ for Security Service Edge.
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 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

Microsoft Office Document Triggering New Zero-Day

Sep 13 2021

Co-Author: Ghanashyam Satpathy


A new zero-day vulnerability (CVE-2021-40444) affecting multiple versions of Windows has recently been discovered and disclosed by Microsoft. According to Microsoft’s Security Update Guide, the MSHTML component can be exploited by an attacker through a custom ActiveX control, allowing remote code execution. This zero-day vulnerability can be triggered through weaponized Office documents and there is evidence of documents exploiting this vulnerability in the wild.

Microsoft has not yet released a security patch, but has released a workaround that can be implemented to protect systems from this vulnerability. You can also use Protected View or Application Guard for Office, either of which can mitigate this issue.

Netskope Threat Protection detects and blocks files related to CVE-2021-40444, protecting our customers from this recently discovered exploit.

This security issue has a severity level (CVSS) of 8.8 out of 10, and in this blog post, we will analyze a malicious Office document that exploits this zero-day vulnerability.


The sample we analyzed was a weaponized Microsoft Word document that was first uploaded to VirusTotal on September 09, 2021, under the name “A Letter before court 4.docx”.

Weaponized Word document.

If Microsoft Protected View isn’t enabled, the vulnerability allows the malicious code to be executed as soon as the victim opens the document, requiring no interaction from the user whatsoever, differently from other kinds of infected Office documents where the victim usually needs to click a button to enable malicious VBA Macros.

By default, Microsoft Office files downloaded from the internet are opened in Protected View or Application Guard for Office, which mitigate the issue unless the user explicitly allows the content from the document.

The text of the document itself is just a decoy, designed to create a sense of urgency to trick the user into opening the document, and realistic enough so that they don’t suspect anything is awry after they open it. 

Weaponized document once it’s opened.

As previously mentioned, the exploit doesn’t require any macros at all, as the malicious script will be loaded automatically by Microsoft Word. By analyzing the network traffic, we can see two GET requests coming from Word’s process.

Network requests from the weaponized document.

At the time of the analysis, both payload URLs were offline, so we simulated a server to deliver all files required for the exploit to work.

Soon after these network requests, we can see the MSHTML DLL being loaded, which according to Microsoft is the component that contains the vulnerability.

Microsoft Word loading “mshtml.dll”.

After the payloads were downloaded, we can see Word’s process spawning “control.exe”, which eventually calls “rundll32.exe”.

Processes spawned by Microsoft Word.

To understand what is happening, we need to take a closer look at the weaponized Word document. The file is in the Office Open XML (OOXML) format, meaning that we can decompress and analyze its elements individually.

Once the file is decompressed, we take a look into the OOXML relationships by following the steps shown in the image below.

Extracting “document.xml.rels” file.

Inside that file, one of the defined relationships stands out before the others, as we can see in the image below.

Relationship pointing to the first payload URL.

This external relationship is the only feature implemented by the attacker in the document. Now, we need to take a look in the “side.html” file.

Weaponized Office document downloading the initial payload.

The “side.html” is an HTML file that contains JavaScript, which is likely the code that triggers the vulnerability. Although we can see some of the variables used by the code, such as the URL for the final payload, it’s difficult to understand what the script is actually doing due to the obfuscation implemented by the attacker.

Part of the “side.html” file downloaded by the document.

After a small deobfuscation, we can see that the code downloads a file named “”, extracts a DLL named “championship.inf”, and then it uses a sequence of path traversal as an attempt to execute the file.

Part of the deobfuscated code from “side.html”.

Analyzing Procmon logs, we can see these calls being executed by the process “control.exe”, trying to load the DLL with “rundll32.exe”.

Eventually, the DLL is executed through “rundll32.dll” and “shell32.dll”, which is a technique mapped in the MITRE ATT&CK as T1218.011, also elaborated by the LOLBAS project.

The final payload (“championship.inf”) is a DLL file, and although this information is not 100% reliable, it seems that the file was compiled on August 20, 2021.

Final payload executed by the weaponized document.

This payload is a Cobalt Strike beacon, connecting to an external address as soon as it’s loaded.

Cobalt Strike C2 Domain.


Netskope Threat Labs is actively monitoring CVE-2021-40444 and has ensured coverage for all known threat indicators and payloads.

  • Netskope Threat Protection
    • Trojan.GenericKD.46912127
    • Trojan.GenericKD.37522535
    • Trojan.GenericKD.46912129
    • DeepScan:Generic.Ursnif.3.1.D4EE9B95
  • Netskope Advanced Threat Protection provides proactive coverage against this threat.
    • Gen.Malware.Detect.By.StHeur indicates a sample that was detected using static analysis
    • Gen.Malware.Detect.By.Sandbox indicates a sample that was detected by our cloud sandbox
    • Gen.Malware.Detect.By.StHeurUrl indicates a sample that was detected by Netskope advanced heuristics.

Below we have an example of a file exploiting CVE-2021-40444, detected by Netskope.



A Letter before court 4.docx938545f7bbe40738908a95da8cdeabb2a11ce2ca36b0f6a74deda9378d380a52

CVE-2021-40444 Exploit URLs

Cobalt Strike C2 Domain

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