Erebus Ransomware targeting Linux Servers

Erebus was first spotted in a spate of malvertising attacks in September 2016 and then reappeared in 2017 using a method to bypass Windows' User Account Control.

Threat ID:: CC-1483
Category:: Adware, Ransomware
Threat Severity:: Medium
Threat Vector:
Published:: 21 June 2017 12:00 AM

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

This content has been archived

This article no longer conforms to NHS Digital's standards for cyber alerts, and may contain outdated or inaccurate information. Use of this information contained in this page is at your own risk

Summary

Erebus was first spotted in a spate of malvertising attacks in September 2016 and then reappeared in 2017 using a method to bypass Windows' User Account Control.

Affected platforms

The following platforms are known to be affected:

Linux

Linux Servers

Threat details

The recent Linux variant was similar to the updated variant discovered with OS-specific changes.

The Windows version leveraged a strategy of bypassing the User Access Controls (UAC) to gain elevated privilege in order to execute. “The Linux version leverages a similar mechanism in Linux, but also adds a fake Bluetooth service to ensure that the ransomware is executed even after the system or server is rebooted.

Files encrypted with Erebus are first scrambled with RC4 encryption in 500kB blocks with randomly generated keys. The RC4 key is then encoded with AES encryption algorithm, which is stored in the file. The AES key is again encrypted using RSA-2048 algorithm that is also stored in the file.

While each encrypted file has its RC4 and AES keys, the RSA-2048 public key is shared. These RSA-2048 keys are generated locally, but the private key is encrypted using AES encryption and another randomly generated key. On-going analysis indicates that decryption is not possible without getting hold of the RSA keys.

Remediation steps

Type	Step
	If a computer on your network becomes infected with Ransomware report it to your AV vendor for analysis and patching. Typically Ransomware will begin encrypting local machine files, mapped network drives and files on any shared network storage 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 report it to your AV vendor for analysis and patching.

Typically Ransomware will begin encrypting local machine files, mapped network drives and files on any shared network storage 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 3:06 pm