Turla group (also known as Waterbug, Venomous Bear and KRYPTON) has been active since at least 2007 targeting government organizations and private businesses.
The list of previously known victims is long and includes also the Swiss defense firm RUAG, US Department of State, and the US Central Command.
Attackers use the LightNeuron malware to access and modify any email passing through the compromised mail server. It also allows create new emails and prevents that messages reach the intended recipients.
Malware researchers believe Turla is using the malware at least since 2014 to target Microsoft Exchange servers. The experts only analyzed a Windows version of the malicious code, but evidence suggests the existence of a Linux version as well.
ESET has identified at least three different organizations that have been infected with the malware, including a Ministry of Foreign Affairs in an Eastern European country, a regional diplomatic organization in the Middle East, and an unknown organization in Brazil.
LightNeuron is the first malware specifically designed to target Microsoft Exchange email servers, it runs with the same level of trust as spam filters and other security products.
LightNeuron supports many commands, including executing processes and commands, writing/executing/deleting files, exfiltrating files, and disabling the backdoor for x minutes.
Attackers control the malware using emails containing specially crafted PDF documents or JPG images as attachments. Commands are hidden in the attachments using
Researchers at ESET pointed out that compromised Exchange servers received commands mostly during work hours in UTC+3, the Moscow time zone. The activity of attackers was temporarily suspended between December 28, 2018, and January 14, 2019, that match the Christmas period for the Orthodox church.
On August, ESET published a detailed report on another variant of the Turla backdoor that leverages email PDF attachments as command and control.