New BitPaymer Ransomware Discovered Hunting Big Game

What do the city of Edcouch, Texas and the Chilean Ministry of Agriculture have in common? Answer: They were both hit in June 2019 by a new ransomware variant identifying itself as BitPaymer.

Crowdstrike has identified this new ransomware as DoppelPaymer since they say that it shares most of its code with the BitPaymer ransomware operated by INDRIK SPIDER. However, there are a number of differences between DoppelPaymer and BitPaymer, which may signify that one or more members of INDRIK SPIDER have split from the group and forked the source code of both Dridex and BitPaymer to start their own Big Game Hunting ransomware operation.

Big Game Hunting is the specific targeting of high-payout, high-value victims.

TA505 is thought to be the main threat group. They are best known for the Dridex Trojan and the Locky ransomware.

In August 2017, Crowdstrike says that the group introduced BitPaymer ransomware and began to focus on leveraging access within a victim organization to demand a high ransom payment.

In November 2018, BitPaymer's file encryption routine was updated to use 256-bit AES in cipher block chaining (CBC) mode with a randomly generated key and a NULL initialization vector. Previous versions of BitPaymer had used 128-bit RC4. The victim-specific RSA public key has also been increased from 1,024-bits to 4,096-bits.

RC4 is considered cryptographically weak when compared to AES. Crowdstrike says that the first known victims of DoppelPaymer were targeted in June 2019, and they were able to recover earlier builds of the malware dating back to April 2019.

The payment portal for DoppelPaymer is almost identical to the original BitPaymer portal. There are obvious similarities between the tactics, techniques and procedures (TTPs) used by DoppelPaymer and prior TTPs of BitPaymer, such as the use of TOR for ransom payment and the .locked extension.

Crowdstrike also says that, "numerous modifications were made to the BitPaymer source code to improve and enhance DoppelPaymer's functionality. For instance, file encryption is now threaded, which can increase the rate at which files are encrypted. The network enumeration code was updated to parse the victim system's Address Resolution Protocol (ARP) table, retrieved with the command arp.exe -a. The resulting IP addresses of other hosts on the local network are combined with domain resolution results via nslookup.exe. (In a similar approach, previous versions of BitPaymer made use of the command net.exe view to enumerate network shares.)"

DoppelPaymer terminates processes and services that may interfere with file encryption.

So, both BitPaymer and DoppelPaymer continue to be operated in parallel. New victims of both ransomware families have been identified by Crowdstrike in June and July 2019. The parallel operations, when coupled with the significant code overlap between BitPaymer and DoppelPaymer that Crowdstrike found, tend to demonstrate not only a fork of the BitPaymer code base, but an entirely separate operation as well.

— Larry Loeb has written for many of the last century's major "dead tree" computer magazines, having been, among other things, a consulting editor for BYTE magazine and senior editor for the launch of WebWeek.