CryTekk Ransomware

First observed in January 2019, CryTekk is a new variant of the HiddenTear ransomware. CryTekk differs from other HiddenTear variants in that the ransom note directs users to a phishing site designed to capture credit card details and personal information.

Threat ID:: CC-2907
Category:: Ransomware
Threat Severity:: Medium
Threat Vector:
Published:: 29 January 2019 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

At the time of publication there is little information available on the method used to deliver the ransomware. However, there are indications it is delivered by spam email campaigns.

CryTekk encrypts files using an AES-256 cipher, before appending them with the “.locked” extension. It attempts to remove Volume Shadow Copies and system restore points before deploying a ransom note named ‘README.html’ to the desktop. Where possible it will attempt to detect the default system web browser and use it to display the ransom note on screen.

The ransom note offers users with two payment options, pay from a cryptocurrency account or PayPal via a "Buy Now" button. Clicking the "Buy Now" button opens a browser tab to a series of phishing pages asking for credit card details and personal information.

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. Open source tools are available which claim to be able to decrypt files encrypted by HiddenTear ransomware and it's variants. However, these tools are not tested by NHS Digital and we cannot guarantee their effectiveness at resolving the problem. Users wishing to use one of these tools do so at their own risk.

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.

Open source tools are available which claim to be able to decrypt files encrypted by HiddenTear ransomware and it's variants. However, these tools are not tested by NHS Digital and we cannot guarantee their effectiveness at resolving the problem. Users wishing to use one of these tools do so at their own risk.

Last edited: 14 February 2020 2:53 pm