Netskope named a Leader in the 2022 Gartner® Magic Quadrant™ for Security Service Edge. Get the Report.

  • Products

    Netskope products are built on the Netskope Security Cloud.

  • Platform

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

Netskope Named a Leader in the 2022 Gartner Magic Quadrant™ for SSE Report

Get the report Go to Products Overview
Netskope gartner mq 2022 sse leader

Netskope delivers a modern cloud security stack, with unified capabilities for data and threat protection, plus secure private access.

Explore our platform
Birds eye view metropolitan city

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

Learn more
Lighted highway through mountainside switchbacks

Prevent threats that often evade other security solutions using a single-pass SSE framework.

Learn more
Lighting storm over metropolitan area

Zero trust solutions for SSE and SASE deployments

Learn more
Boat driving through open sea

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

Learn more
Wind turbines along cliffside
  • 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.

  • 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 more
Netskope Professional Services

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

Learn more
Group of young professionals working
  • 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

Episode 14: Enabling Security from the Top-Down

Play the podcast
Black man sitting in conference meeting

Read the latest on 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

Netskope is positioned to help you begin your journey and discover where Security, Networking, and Zero Trust fit in the SASE world.

Learn more
SASE Week

What is Security Service Edge?

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

Learn more
Four-way roundabout
  • 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.

Netskope enables the future of work.

Find out more
Curvy road through wooded area

Netskope is redefining cloud, data, and network security to help organizations apply Zero Trust principles to protect data.

Learn more
Switchback road atop a cliffside

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 more
Group of diverse young professionals smiling

Khonsari: New Ransomware Delivered Through Log4Shell

Dec 16 2021

Summary

While many organizations are patching the two recent Apache Log4j vulnerabilities (CVE-2021-44228 and CVE-2021-45046), attackers have been racing to exploit them to deliver malware, such as botnets, backdoors, and cryptominers.

Among the threats delivered using Log4Shell exploits, a new ransomware family was found by Bitdefender: Khonsari. For now, only a Windows version of the malware was found, first spotted on December 11th, where attackers were using the CVE-2021-44228 vulnerability to deliver the executable. Microsoft has also spotted a few cases where Khonsari was being launched from compromised Minecraft clients.

At this point, Khonsari appears to be an individual effort, not working in the popular Ransomware-as-a-Service (RaaS) model, used by REvil, LockBit, BlackMatter, and Hive

Log4Shell

The first file involved in the attack was named “Main.class”, which is a Java downloader being delivered through Log4Shell.

Screenshot of Log4Shell pattern that could be used to deliver Khonsari
Log4Shell pattern that could be used to deliver Khonsari

The Java file is a simple downloader, and two days after Khonsari was first spotted, December 13th, the attackers changed the “Main.class” file to deliver another malware known as Orcus RAT.

Screenshot of Java file delivered through Log4Shell, downloading Orcus RAT.
Java file delivered through Log4Shell, downloading Orcus RAT.

Khonsari Ransomware

The ransomware was developed in .NET, where the attacker has manipulated the compiled time date stamp to 46 years in the future.

Screenshot of Khonsari binary details.
Khonsari binary details.

The malware developer has used minor obfuscation to hide some classes, functions, and variable names.

Screenshot of Decompiled Khonsari.
Decompiled Khonsari.

All the strings used by the ransomware are encrypted, using a quite simple rolling XOR algorithm, which can be represented by the following Python code:

Screenshot of decrypting Khonsari strings.
Decrypting Khonsari strings.

As soon as it runs, Khonsari sends a network request to an external server.

Screenshot of the first action in Khonsari’s main function.
The first action in Khonsari’s main function.

This is probably just for metrics, as no data is sent or received in this process. Also, we noticed that the process crashes if the URL doesn’t respond, meaning that this URL can be added to blocklists to prevent the ransomware execution.

Screenshot of network request sent by Khonsari.
Network request sent by Khonsari.

After the network request, Khonsari enumerates all available drives that are different from “C:\”. Then, it creates a list containing the directories that will be encrypted, such as Downloads, Desktop, Videos, Pictures, etc.

Screenshot of Khonsari building a list of directories.
Khonsari building a list of directories.

With all the directories enumerated, Khonsari starts the encryption process (each step listed is highlighted in the figure below):

  1. Iterating over the files in each directory;
  2. Reading and encrypting the file contents;
  3. Renaming the file to add the “khonsari” extension;
  4. Once the loop is done, it creates the ransom note, opening it automatically.
Screenshot of Khonsari encryption routine.
Khonsari encryption routine.

Throughout this process, Khonsari also checks the file extension before encrypting it. In the binary we analyzed, it skips the encryption if the file ends with “.khonsari”, “.ini”, and “ink”.

Screenshot showing that Khonsari skips the encryption according to the file’s extension.
Khonsari skips the encryption according to the file’s extension.

The last one seems to be a typo, as the developer probably wanted to skip “.lnk” files. However, this one encrypts links anyway, as the string checked by the code is “ink”.

Screenshot of Khonsari encrypting “.lnk” files
Khonsari encrypting “.lnk” files

For encryption, Khonsari uses AES 128 to encrypt the files, and RSA to encrypt the keys. This is how the flow works:

  1. The AES key and IV is generated once Khonsari runs;
  2. AES is then used to encrypt all the files, using both the key and IV previously generated;
  3. Khonsari encrypts both AES key and IV using a public RSA key hardcoded in the binary;
  4. The encrypted key and IV are then encoded with base64 and stored within the ransom note.
Screenshot of Khonsari AES + RSA encryption.
Khonsari AES + RSA encryption.

Once done, Khonsari creates the ransom note with the instructions along with the information to recover the files (encrypted/encoded AES key + IV).

Screenshot of ransomware creating the ransom note.
Ransomware creating the ransom note.

Khonsari opens the ransom note automatically to display the message to its victims.

Screenshot of Khonsari ransom note.
Khonsari ransom note.

If the user accidentally deletes the ransom note, the decryption of the files is impossible, since the key is stored along with the recovery message.

Conclusion

The vulnerabilities discovered in Apache Log4j are a nightmare for people and organizations around the world. It was just a matter of time before we start seeing Log4Shell being used to deliver threats, like Khonsari. We should be on the lookout for more threats that are abusing this vulnerability, as well as patch all systems using Log4j as soon as possible to mitigate the risks. Furthermore, Khonsari related URLs should be blocked, as the threat doesn’t work when the network request fails.

Protection

Netskope Threat Labs is actively monitoring this campaign and has ensured coverage for all known threat indicators and payloads. 

  • Netskope Threat Protection
    • ByteCode-MSIL.Ransomware.Khonsari
  • 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

IOCs

A full list of IOCs and a Yara rule are all available in our Git repo.

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.