Embedded C# Ransomware

A new ransomware tool has been discovered that uses embedded C# code that compiles at runtime instead of a distributed executable.

Threat ID:: CC-2319
Category:: Ransomware
Threat Severity:: Low
Threat Vector:
Published:: 30 April 2018 12:00 AM

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Summary

A new ransomware tool has been discovered that uses embedded C# code that compiles at runtime instead of a distributed executable.

Affected platforms

The following platforms are known to be affected:

Microsoft Windows

Microsoft Windows - All versions

Threat details

The tool appears to still be in development but is functionally able to encrypt files.

The unnamed tool is delivered via a malware dropper, although it is unclear how this is distributed to users. This dropper contains an encrypted string and a hard-coded key. When decrypted this string contains the source code for the malware. It is believed this method is used to prevent detection of the dropper by security products.

The C# code is then compiled and begins an encryption process targeting all available local files. Filenames are converted to hexadecimal and prepended with the phrase 'sequre.io[Filename]_'.

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 on the basis 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 on the basis 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.

Last edited: 17 February 2020 12:42 pm