Russian-linked APT group Turla has used a previously undocumented malware toolset, named Crutch, in cyberespionage campaigns aimed at high-profile targets, including the Ministry of Foreign Affairs of a European Union country.
The Turla APT group (aka Snake, Uroburos, Waterbug, Venomous Bear and KRYPTON) has been active since at least 2007 targeting diplomatic and government organizations and private businesses in the Middle East, Asia, Europe, North and South America, and former Soviet bloc nations.
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.
The Crutch framework was employed in attacks since 2015 to siphon sensitive data and transfer them to Dropbox accounts controlled by the Russian hacking group. ESET researchers speculate Crutch is not a first-stage backdoor and operators deployed it only after they have gained access to the target’s network.
“During our research, we were able to identify strong links between a Crutch dropper from 2016 and Gazer. The latter, also known as WhiteBear, was a second-stage backdoor used by Turla in 2016-2017.” reads the report published by ESET.
ESET researchers linked Crutch to the Russia-linked APT Turla based on similarities (both samples dropped on the same machine with a five-day interval in September 2017, they drop CAB files containing malware components and a loader that share the same PDP paths, and use the same RC4 key tp decrypt the payloads.
Experts also observed the presence of FatDuke and Crutch at the same time on one machine. FatDuke is a third-stage backdoor that was attributed to the Dukes/APT29, experts believe that both Russia-linked APT groups independently compromised the same machine.
The analysis of the timestamps of 506 ZIP archives uploaded to the Dropbox accounts and containing data stolen between October 2018 and July 2019, revealed the working hours of the attackers, which is UTC+3 time zone (Russia).
Experts believe that Turla attackers used Crutch as a second stage backdoor, while first-stage implants used by the APT group includes Skipper (2017) and the open-source PowerShell Empire post-exploitation framework (from 2017)
Crutch versions employed between 2015 to mid-2019 used backdoor channels to communicate with hardcoded Dropbox account via the official HTTP API and drive monitoring tools that are able to search for certain documents of interest.
In July 2019, experts spotted a new version of Crutch (tracked as ‘version 4’) that no longer supports backdoor commands and added a removable-drive monitor with networking capabilities.
“The main difference is that it no longer supports backdoor commands. On the other hand, it can automatically upload the files found on local and removable drives to Dropbox storage by using the Windows version of the Wget utility.” continues the analysis.
Version 4, like the previous one, uses DLL hijacking to gain persistence on compromised devices on Chrome, Firefox, or OneDrive.
“Crutch shows that the group is not short of new or currently undocumented backdoors. This discovery further strengthens the perception that the Turla group has considerable resources to operate such a large and diverse arsenal.” concludes the report that also provides IoCs for the attacks.
“Crutch is able to bypass some security layers by abusing legitimate infrastructure – here Dropbox – in order to blend into normal network traffic while exfiltrating stolen documents and receiving commands from its operators.”
(SecurityAffairs – hacking, Crutch)