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GandCrab Ransomware
First observed in January 2017, GandCrab is a ransomware tool delivered by a number of exploit kits including RIG and GrandSoft, as well as by the Necurs botnet.
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This article no longer conforms to NHS Digital's standards for cyber alerts, and may contain outdated or inaccurate information.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


First observed in January 2017, GandCrab is a ransomware tool delivered by a number of exploit kits including RIG and GrandSoft, as well as by the Necurs botnet.

Affected platforms

The following platforms are known to be affected:

Threat details

Once installed, GandCrab creates a registry entry so that it runs at start-up before collecting the following information:

  • user and computer name
  • keyboard type
  • presence of antivirus
  • processor type and architecture
  • IP Address
  • OS version
  • disk space
  • system language
  • active drives
  • locale

Files are encrypted using the RSA algorithm, with the public and private keys generated using API calls to standard Microsoft libraries. The ransom note demands payment in Dash, a less widely used cryptocurrency.

Threat updates

Date Update
14 Mar 2018

A new variant of GandCrab has been observed using a new file extension, .CRAB, as well as new ransom notes and Tor payment sites.

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.


A free decrypter for GandCrab has been released through the NoMoreRansom project. Organisations are advised that NHS Digital do not test decryption tools and that they use them at their own risk.


To prevent GandCrab from using the ETERNALBLUE exploit: 

  • Block SMB related ports (UDP 137, 138  and TCP 137, 139, 445) at your organisation's external firewall
  • Use a port scanner to confirm UDP 137, 138  and TCP 139, 445 are locked down
  • Ensure all affected platforms are updated in line with the Microsoft security bulletin MS17-010.  Microsoft has additionally recommended updating with all security patches released within the last 60 days - internet and N3 facing systems should be prioritised.  Because of the high severity of this vulnerability Microsoft has taken the highly unusual step of releasing a patch for out of support operating systems including Windows XP, Windows 8, and Windows Server 2003. For further information see Microsoft Customer guidance for WannaCry attacks
  • Use a vulnerability scanner (such as Nessus, OpenVas or Microsoft Baseline Security Analyser) to identify any unpatched systems.
  • Follow Microsoft's guidance How to verify that MS17-010 is installed
  • If it is not possible to apply this patch then block SMB related ports (UDP 137, 138 and TCP 139, 445) across your organisation's network or disable SMB
  • If your organisation has SMB port 445 exposed on any system then review if this is operationally necessary (including the use of NetBIOS ports UDP 137 & 138 and NetBIOS over TCP/IP TCP Ports 137 & 139) as SMB and NetBIOS are both legacy protocols that may no longer be required within your environment.
  • If  you are using SMBv1 in your environment (which is now 30 years old and lacks security features of later version) migrate to a more secure SMB version as described in the Microsoft Blog - Stop using SMB1


A new tool, capable of decrypting GandCrab versions V1, V4 and V5 files, has been released by the NoMoreRansom project. Organisations are advised that NHS Digital do not test decryption tools and that they use them at their own risk.

Last edited: 17 February 2020 12:43 pm