Members of the cybercriminal group behind the infamous Dridex Trojan have split from the gang and released a forked version of the BitPaymer ransomware, CrowdStrike reports.
Referred to as TA505 and best known for the Dridex Trojan and the Locky ransomware, the threat actor has been releasing various new malware families lately, including the tRat backdoor and the AndroMut downloader.
After the release of ransomware variants Bart in 2016 and Jaff in May 2017, the cybercriminals released BitPaymer (also known as FriedEx) in mid-2017. This piece of ransomware focused on high profile targets and companies rather than end users and was being distributed through Remote Desktop Protocol (RDP) brute force attacks.
Now, a new variant of this ransomware has emerged, suggesting that some members of TA505 left the group and forked the source code of both Dridex and BitPaymer to start their own operation. Dubbed DoppelPaymer, the new ransomware variant is strikingly similar to the original.
First identified in August 2017, BitPaymer initially delivered a ransom note with the ransom demand and a URL for a TOR-based payment portal. Both the ransom amount and the payment portal URL were removed from the note over time. Since July 2018, the note has only included two emails to negotiate the ransom.
In November 2018, the ransom note was updated to include the victim’s name. The file extension appended to encrypted files was customized to use a representation of the victim’s name. The malware also adopted 256-bit AES in cipher block chaining (CBC) mode for encryption.
The threat actor has used this updated version of BitPaymer in at least 15 confirmed ransomware attacks that continued throughout 2019 and involved incidents occurring in June and July 2019 as well.
DoppelPaymer was first used in a targeted attack in June 2019, but the security researchers were able to recover earlier builds dating back to April 2019, which might have been built for testing. A total of eight distinct malware builds have been identified, and three victims confirmed.
The victims were asked different ransom amounts, namely 2, 40, and 100 BTC, respectively. At current exchange rates, the actors demanded from approximately $25,000 to over $1,200,000 from their victims.
The ransom note in DoppelPaymer is similar to those used of BitPaymer in 2018. No ransom amount is included, but users are provided a URL for a TOR-based payment portal that looks almost identical to the original BitPaymer portal.
DoppelPaymer’s authors made a series of changes to the BitPaymer source code to improve the ransomware’s functionality. File encryption is now threaded to increase speed, the network enumeration code was updated, and the malware was designed to only run after a specific command line argument has been provided.
The threat also terminates processes and services that may interfere with the file encryption. For this, the ransomware uses ProcessHacker, a legitimate open-source administrative utility.
Another interesting discovery that CrowdStrike made was that DoppelPaymer’s code suggests a connection with a new variant of Dridex that has emerged in attacks over the past couple of months.
“Both BitPaymer and DoppelPaymer continue to be operated in parallel and new victims of both ransomware families have been identified in June and July 2019. The parallel operations, coupled with the significant code overlap between BitPaymer and DoppelPaymer, indicate not only a fork of the BitPaymer code base, but an entirely separate operation,” CrowdStrike concluded.