Sigma Ransomware

Sigma is a newly observed ransomware that is delivered via protected Microsoft Word or Rich Text Format documents spread through phishing emails.

Threat ID:: CC-2167
Category:
Threat Severity:: Low
Threat Vector:
Published:: 22 March 2018 12:00 AM

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Summary

Sigma is a newly observed ransomware that is delivered via protected Microsoft Word or Rich Text Format documents spread through phishing emails.

Affected platforms

The following platforms are known to be affected:

Microsoft Windows

Microsoft Windows - All Versions

Threat details

When the user downloads and opens the file with the password provided, it will promptly ask to enable macros and when enabled this activates an embedded Visual Basic Script that downloads the Sigma ransomware to the computer. Once downloaded it will extract and run the extracted svchost.exe which will start encrypting files.

Unlike most ransomwares, these files will not have a new file extension but will include a file marker and what appears to be an encrypted key at the bottom of each file.

Threat updates

Date	Update
8 May 2018	Updates A new version of Sigma has been observed to be using more sophisticated phishing techniques that involves including the user's name inside of the email making them more believable. This new version also makes the body of the email message an inline image in an attempt to avoid anti-spam scanners.

Remediation steps

Type	Step
	If a computer 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, antivirus 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 infected machine and unplugging / 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 PC). 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 computer 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, antivirus 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 infected machine and unplugging / 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 PC).

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: 11 January 2022 9:28 am