The United States has seized two command-and-control (C2) and malware distribution domains used in a recently disclosed spearphishing campaign that impersonated email communications from the US Agency for International Development (USAID), the Department of Justice reports.
Microsoft and Volexity disclosed the attack late last week. This operation has been attributed to a group Microsoft calls Nobelium, the Russian group behind the SolarWinds supply chain attack. It has been operating and evolving this emailed campaign since early 2021, Microsoft reports. The ongoing attack has targeted approximately 350 organizations across industries, the Department of Homeland Security's Cybersecurity and Infrastructure Security Agency (CISA) confirmed in a May 28 statement.
Attackers gained access to USAID's account for Constant Contact, a legitimate platform used for email marketing. Their access allowed them to send seemingly authentic emails from USAID containing a "special alert" to thousands of target accounts and hide malicious links behind the mailing service's URL.
Victims who clicked this link were prompted to download malware from a subdomain of theyardservice[.]com, the DoJ reports. With this foothold, attackers downloaded a Cobalt Strike tool to remain persistent and possibly deploy additional tools or malware to a target network.
Officials note the attackers' instance of the Cobalt Strike tool received C2 communications via other subdomains of theyardservice[.]com and the domain worldhomeoutlet[.]com. These two domains were seized following the court-ordered seizure.
The court-authorized seizure of these two domains was intended to disrupt attackers' follow-on exploitation of victims and identify compromised machines, officials write in a release. They note attackers may have deployed "additional backdoor accesses" between the time of initial compromise and last week's seizure.
Security researchers have been taking a closer look at the tools used in this campaign to learn more about how these attackers operate. Each of these tools is designed for flexibility, letting attackers adapt to operational challenges they might face, the Microsoft Threat Intelligence Center (MSTIC) explains in a blog post. Its researchers identify four of these tools in Nobelium's infection chain: EnvyScout, BoomBox, NativeZone, and VaporRage.
"While its technical specifics are not unprecedented, Nobelium's operational security priorities have likely influenced the design of this toolset, which demonstrate preferable features for an actor operating in potentially high-risk and high-visibility environments," researchers wrote.
For Nobelium, these priorities include the use of trusted channels. For example, attackers rely on Boombox, a downloader used to obtain a later-stage payload from a Dropbox account they control. All initial communications use the Dropbox API via HTTPS, researchers noted.
They also value the opportunity for restraint. Like other tools used by this group, Boombox, VaporRage, and some variants of NativeZone do some profiling on a target's environment. It's plausible, researchers said, that this design allows Nobelium to choose its targets and learn if they could be discovered if the implant is deployed in environments unfamiliar to attackers.
And finally, the attackers value ambiguity. VaporRage is a "unique shellcode loader" seen as the third-stage payload, MSTIC reported, and it can download, decode, and execute an arbitrary payload fully in-memory.
"Such design and deployment patterns, which also include staging of payloads on a compromised website, hamper traditional artifacts and forensic investigations, allowing for unique payloads to remain undiscovered," researchers wrote.
Of course, these aren't the only tools Nobelium relies on. Since December, security researchers across the industry have identified a growing pool of payloads the group uses. These include Teardrop, Sunspot, Raindrop, FlipFlop, GoldMax, GoldFinder, and Sibot malware.
Research into the attackers' tools is still ongoing. The team with SentinelLabs, which refers to the group as NobleBaron, has found one of the NativeZone downloaders is being used as part of a "clever poisoned installer" targeting Ukrainian government security applications. As Juan Andrés Guerrero-Saade wrote in a blog post, a malicious DLL was designed to impersonate a legitimate component of the Ukrainian Institute Technology's cryptographic keys.