Netwalker Ransomware

First observed in late 2019, Netwalker (also known as Kazakavkovkiz or KoKo) is a fileless ransomware-as-a-service tool primarily targeted at enterprise targets in Western Europe and the USA. Whilst it was previously known as Mailto, the name was changed when Netwalker's creators began offering its services to affiliate users through a number of dark web sites.

Threat ID:: CC-3360
Category:: Ransomware
Threat Severity:: Medium
Threat Vector:: Download
Published:: 6 February 2020 12:00 AM

Report a cyber attack: call 0300 303 5222 or email [email protected]

Summary

Affected platforms

The following platforms are known to be affected:

Microsoft Windows

Microsoft Windows - All versions

Threat details

Unlike most MaaS ransomware, Netwalker's creators only offer it to affiliates with substantial network intrusion experience and prior access to target networks. Whilst this substantially reduces the number of potential affiliates Netwalker can be sold to, this seems to be a tactic to increase the monetary value of each individual attack, as well as limiting Netwalker's exposure to security agencies.

Netwalker is provided to affiliates as a heavily obfuscated and encrypted PowerShell script, which when executed uses reflective DLL injection to insert itself into a running explorer.exe process. It then attempts to exfiltrate data from a number of specified directories before deleting any Volume Shadow Copies. If successful, Netwalker begins to encrypt all non-system files using an unknown algorithm.

Information stolen by Netwalker is automatically posted to the MEGA file sharing site after an affiliate-specified countdown has elapsed.

For further information:

ACSC Advisory 2020-003

Update 25 Mar 3030

Mailto is now being delivered in a number of new Covid-related spam campaigns against healthcare and government organisations,

Remediation steps

Type	Step
	If a device on your network becomes infected with ransomware it will begin encrypting local machine files and files on any network the logged-in user has permission to access. For system administration accounts this may include backup storage locations. To avoid becoming infected with ransomware, ensure that: A robust program of education and awareness training is delivered to users to ensure they don’t open attachments or follow links within unsolicited emails. All operating systems, anti-virus and other security products are kept up to date. All day to day computer activities such as email and internet are performed using non-administrative accounts and that permissions are always assigned based on the principle of least privilege. Your organisation adopts a holistic all-round approach to Cyber Security as advocated by the 10 Steps to Cyber Security. Identifying the source of infection: Identifying the affected device and disconnecting or quarantining it from the network is essential to damage limitation. Users should immediately report infections to their IT support provider, disconnect their network cable and power the computer down. File auditing should be enabled, and file server logs should be monitored to detect signs of unauthorised encryption and allow the source of encryption to be identified (i.e. the infected device). To limit the damage of ransomware and enable recovery: All critical data must be backed up, and these backups must be sufficiently protected/kept out of reach of ransomware. Multiple backups should be created including at least one off-network backup (e.g. to tape). The only guaranteed way to recover from a ransomware infection is to restore all affected files from their most recent backup.

Type

Step

If a device on your network becomes infected with ransomware it will begin encrypting local machine files and files on any network the logged-in user has permission to access. For system administration accounts this may include backup storage locations.

To avoid becoming infected with ransomware, ensure that:

A robust program of education and awareness training is delivered to users to ensure they don’t open attachments or follow links within unsolicited emails.
All operating systems, anti-virus and other security products are kept up to date.
All day to day computer activities such as email and internet are performed using non-administrative accounts and that permissions are always assigned based on the principle of least privilege.
Your organisation adopts a holistic all-round approach to Cyber Security as advocated by the 10 Steps to Cyber Security.

Identifying the source of infection:
Identifying the affected device and disconnecting or quarantining it from the network is essential to damage limitation.

Users should immediately report infections to their IT support provider, disconnect their network cable and power the computer down.
File auditing should be enabled, and file server logs should be monitored to detect signs of unauthorised encryption and allow the source of encryption to be identified (i.e. the infected device).

To limit the damage of ransomware and enable recovery:
All critical data must be backed up, and these backups must be sufficiently protected/kept out of reach of ransomware.

Multiple backups should be created including at least one off-network backup (e.g. to tape).
The only guaranteed way to recover from a ransomware infection is to restore all affected files from their most recent backup.

Indicators of compromise

Main indicators

Netwalker IoC List 17/06/2020

Last edited: 29 June 2021 12:00 pm