Security researchers discovered an attack campaign in which APT41 distributed the Speculoos backdoor by exploiting CVE-2019-19781.

Palo Alto Networks’ Unit 42 discovered the Speculoos backdoor while investigating an attack campaign from APT41 that targeted a variety of organizations in North America, South America and Europe. The campaign exploited CVE-2019-19781, a vulnerability affecting certain Citrix appliances that enabled a malicious actor to remotely execute arbitrary commands. This vulnerability first garnered public attention in mid-December 2019 and received a permanent fix by the end of January 2020. It’s around that time when this campaign began.

Upon successful implementation, the backdoor payload connected to its command-and-control (C&C) server and completed a TLS handshake. At that point, the malware fingerprinted the system and sent this information back to its C&C server. Once it received a response, Speculoos entered into a loop for the purpose of receiving commands such as instructions to create a remote shell, kill a process and/or delete a file, among other functionality.

A Look at APT41’s Other Attack Activity

This isn’t the first time that APT41 has garnered the attention of the security community. Back in August 2019, for instance, FireEye released a report in which it detailed the threat group’s efforts to perpetrate digital espionage using non-public malware against financial organizations.

In March 2020, FireEye detailed the attack campaign discussed by Unit 42 above. That operation lasted until March 11, although FireEye observed a lull in APT41’s activity during the last week of January.

Defending Against the Speculoos Backdoor Campaign

Security professionals can defend their organizations against the Speculoos backdoor campaign uncovered by Unit 42 by using thoughtful prioritization when it comes to their patch management programs. As part of this effort, teams need to prioritize applications that are critical to the business and those that would cause the greatest disruption if they were attacked.

Infosec personnel should also consider using threat intelligence to learn about the tactics, techniques and procedures (TTPs) of attack groups like APT41. This information can then help them spot instances of lateral movement and other malicious activity when they’re in motion.

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