Netskope extends data protection leadership with acquisition of Dasera. Read the press release

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
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
Aerial view of a city
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 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

The Future of Security: Quantum, AI, and Macro-political Change
Emily Wearmouth and Max Havey speak with Netskope CEO Sanjay Beri and CTO Krishna Narayanaswamy about the future of security.

Play the podcast Browse all podcasts
The Future of Security: Quantum, AI, and Macro-political Change
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

Zepto variant of Locky ransomware delivered via popular Cloud Storage apps

Jul 19 2016
Tags
Cloud Best Practices
Cloud Malware
Cloud Security
Locky
Netskope Threat Research Labs
Ransomware
Tools and Tips
Vulnerability Advisory
Zepto

Netskope Threat Research Labs has detected a new strain of the Zepto ransomware shared among cloud users. As has been the trend in recent months, this strain of Zepto arrives at its destination via spam emails that use enticing messages and filenames to encourage the recipient to open the email and download the infected file. These files use an extension of .wsf, which causes Windows to assign an icon that appears similar to a spreadsheet icon. This icon, coupled with a filename of spreadsheet_286..wsf may cause all but the most attentive recipient to view the attachment as legitimate. These messages are then shared among colleagues using cloud SaaS applications such as Microsoft OneDrive, Google Drive, Box, Dropbox, etc.

We have observed sharing and collaboration in cloud apps to represent an often ill-considered secondary propagation vector for malware. Once the spreadsheet_286..wsf file is shared in the cloud, share recipients could easily assume that this “spreadsheet” originated locally and was legitimate, causing the malware to be executed within the protected domain.

Zepto has been observed spreading through “.wsf” (Windows Script File) files within the archive unlike regular JavaScript files. Upon execution, the Windows Script File is executed by Microsoft Windows Script Host which allows mixing the scripting languages JScript and VBScript within a single file. This interlacing of languages permits the attacker to evade detection engines reliant upon emulation of one language.

Netskope Active Threat Protection detected a zip file being shared on Microsoft OneDrive containing a malicious script file with .WSF (Windows Script File) extension. As shown in Figure 1, this WSF file was named spreadsheet_286 with two “.” s in the extension.  

Figure 1Figure 1: Zip attachment with .wsf file inside

The script file starts with <job>tag and is heavily obfuscated. The obfuscated JavaScript code is shown in Figure 2 below:

Figure 2

Figure 2: Obfuscated WSF script code

Once the WSF script is de-obfuscated, the outer layer code looks as shown in Figure 3 below.

Figure 3

Figure 3: De-obfuscated script code

The script is again encoded using string substitution encoding, where strings are split into multiple variables. The above decoded script has many interesting strings being broken into different variables just to make manual analysis more difficult. By looking at the interesting variables with strings like “http” we are able to echo those variables using “WScript.Echo()” to understand behavior of this script. A closer look at the de-obfuscated code reveals  some interesting variables as shown in Figure 4  below:

Figure 4Figure 4: URLs split into different variables

The URLs are split into different named variables and we can find references to these variables in our script as shown in Figure 5 below:

Figure 5Figure 5: URL variables concatenated into one variable

Once we echo interesting variables, the script reveals its malicious purpose as shown in Figure 6 & 7 below:

Figure 6Figure 6: Compromised domains list

Figure 7Figure 7: Temp file name for Zepto

As shown above, the script will download the main payload of Zepto which is in custom encrypted format from any of these 3 compromised domains, decrypt it using code shown in Figure 8 below, performs some validity checks and will save that under %TEMP% folder with name “HRKFnZpT.exe” to execute it later. The DecryptFile code after some string substitutions is shown in Figure 8 below:

Figure 8

Figure 8: DecryptFile code and MZ file Check code

Figure 9

Figure 9: Script routine to execute malicious Zepto payload

The Zepto will only run its main payload if the correct parameter “321” is supplied. This is quite similar to the way Locky ransomware executes its payload. The script routine to execute the payload is shown in Figure 9. This sample didn’t execute under VMware even after correct parameter was supplied to the script. It suggests the presence of anti-VM checks inside the binary. After opening it under OllyDbg, we found several calls to RDTSC (Read Time Stamp Counter) assembly instructions as shown in Figure 10 below:

Figure 10

Figure 10: Calls to RDTSC instructions

Once we bypass this anti-VM checks, the malicious Zepto payload executes itself. It collects system information and sends it across to the attackers IP as shown in Figure 11 below:

Figure 11

Figure 11: System data to be sent over network before encryption

The above information is encrypted and sent to “upload/_dispatch.php” of hard-coded IP addresses as shown in Figure 12 and 13 below:

Figure 12

Figure 12: Hard-coded IP list and PHP file path

Figure 13

Figure 13: Network traffic sent to Zepto C&C

Once the information is sent to Zepto’s C&C server, it will respond back with the RSA key that is used for encryption. The response itself is encrypted as seen in Figure 13 above. The decrypted response is shown in Figure 14 below:

Figure 14

Figure 14: Decrypted first response from C&C

Zepto will use the RSA key and start encrypting files (excluding Windows and System files) with a “.zepto” extension and also the Victim ID as the filename prefix as shown in Figure 15 below:

Figure 15

Figure 15: Encrypted files with .zepto extensions

It will drop two files on the desktop of the victim named “_HELP_instructions.bmp” and “_HELP_instructions.html”. It will open a ransom warning page and set it as the desktop’s wallpaper. The ransom notes are shown in Figure 16 & 17.

Figure 16

Figure 16: Zepto ransom warning HTML page

Figure 17

Figure 17: Zepto ransom warning wallpaper

Zepto encrypts all the files that match the file extensions shown in Figure 18 below:

Figure 18

Figure 18: Zepto file extensions lists

Is Zepto using similar code to Locky?

There are a number of elements which confirm Zepto to be a slightly modified version of Locky:

  1. The use of the “321” parameter to run its main payload
  2. The use of RTDSC instructions to bypass VM
  3. Collecting similar system information, encryption and upload mechanism
  4. Similar ransom note warning and wallpaper
  5. Mention of the Locky decryptor on Zepto ransom page as shown in Figure 19 below:
    Figure 19Figure 19: Zepto ransom payment page
  6. The presence of strings “_Locky_recover_instructions.bmp” and “_Locky_recover_instructions.txt” inside memory of Zepto ransomware as shown in Figure 20 below:
Figure 20

Figure 20: Memory strings inside Zepto binary

All of the above confirm that Zepto is a variant of Locky which uses “.zepto” extensions for encrypted files. Ransomware authors are very active and moving to different delivery mechanisms to bypass scanning engines.

Netskope’s Detection & Remediation

Netskope Active Threat Protection will detect this threat as “Backdoor.Backdoor.Downloadr.DPW”.

Netskope recommends that its users create a policy to block access to extensions such as .wsh, .js, and .vbs. These policy alerts will appear as follows:

Fig 21 Netskope policy violation

Figure 21: Netskope policy violation for sharing files of this type.

Indicators of Compromise (IOCs)

Zepto downloaded encrypted binary

MD5: 6968F0AF128C27C6C970ADC0B301D204

Main Zepto decrypted binary

MD5: 13BF5D82676026EFCF47C411D6C4429C

WSF File

MD5: 7340EFCB3B352CD228A77782C74943A4

Compromised Domains:

hxxp://mystyleparrucchieri.com/b1wm24b
hxxp://intracorp.ca/wf5oo4
hxxp://sophoula.com/e6yscv

C&C IPs:

77.222.54.202
91.209.77.166
185.118.66.83
5.187.0.137
185.5.250.135

Stay informed!

Subscribe for the latest from the Netskope Blog