A new version of GandCrab ransomware (GandCrab v5) has been released. GandCrab is a popular ransomware threat that is offered to affiliates under the ransomware-as-a-service distribution model. Affiliates receive a cut of the profits from any ransoms payed by individuals they manage to infect.

GandCrab was first released in January 2018 and fast grew into one of the most widely used ransomware variants. In July it was named the top ransomware threat and is regularly updated by the authors.

There have been several changes made in GandCrab v5, including the change to a random 5-character extension for encrypted files. The ransomware also uses an HTML ransom note rather than dropping a txt file to the desktop.

Bitdefender released free decryptors for early versions of the ransomware, although steps were taken by the authors to improve security for version 2.0. Since version 2.0 was released, no free decryptors for GandCrab ransomware have been developed.

Recovery from a GandCrab v5 infection will only be possible by paying the ransom – approximately $800 in the Dash cryptocurrency – or by restoring files from backups. Victims are only given a limited time for paying the ransom before the price to decrypt doubles. It is therefore essential that backups are created of all data and for those backup files to be checked to make sure files can be recovered in the event of disaster.

Since this ransomware variant is offered under the ransomware-as-a-service model, different vectors are used to distribute the ransomware by different threat actors. Previous versions of the ransomware have been distributed via spam email and through exploit kits such as RIG and GrandSoft. GandCrab v5 has also been confirmed as being distributed via the new Fallout exploit kit.

Traffic is directed to the exploit kit using malvertising – malicious adverts that redirect users to exploit kits and other malicious websites. These malicious adverts are placed on third party advertising networks that are used by many popular websites to provide an extra income stream.

Any user that clicks one of the malicious links in the adverts is redirected to the Fallout exploit kit. The Fallout exploit kit contains exploits for several old vulnerabilities and some relatively recent flaws. Any user that has a vulnerable system will have GandCrab ransomware silently downloaded onto their device. Local files will be encrypted as well as files on all network shares, not just mapped drives.

Whenever a new zero-day vulnerability is discovered it doesn’t take long for an exploit to be incorporated into malware. The publication of proof of concept code for a Task Scheduler ALPC vulnerability was no exception. Within a couple of days, the exploit had already been adopted by cybercriminals and incorporated into malware.

The exploit for the Task Scheduler ALPC vulnerability allows executable files to be run on a vulnerable system with System privileges and has been incorporated into GandCrab v5. The exploit is believed to be used to perform system-level tasks such as deleting Windows Shadow Volume copies to make it harder for victims to recover encrypted files without paying the ransom. Microsoft has now issued a patch to correct the flaw as part of its September Patch Tuesday round of updates, but many companies have yet to apply the patch.

The most important step to take to ensure that recovery from a ransomware attack is possible is to ensure backups are created. Without a viable backup the only way of recovering files is by paying the ransom. In this case, victims can decrypt one file for free to confirm that viable decryption keys exist. However, not all ransomware variants allow file recovery.

Preventing ransomware infections requires software solutions that block the main attack vectors. Spam filtering solutions such as SpamTitan prevent malicious messages from being delivered to inboxes. Web filters such as WebTitan prevent end users from visiting malicious sites known to host exploit kits. Remote desktop services are often exploited to gain system access, so it is important that these are disabled if they are not required, and if they are, they should only be accessible through VPNs.

Patches should be applied promptly to prevent vulnerabilities from being exploited and advanced antimalware solutions should be deployed to detect and quarantine ransomware before files are encrypted.