The group behind last year's SolarWinds supply chain attack is conducting an advanced and widespread email campaign that delivers malicious links while impersonating the US Agency for International Development (USAID), Microsoft reports.

Microsoft's Threat Intelligence Center (MSTIC) says it has been tracking this Nobelium-operated campaign since January 2021 and it has evolved as the group experiments with new tactics. The phishing attack has so far targeted some 3,000 accounts at more than 150 organizations across several industry verticals. The victims span 24 countries, though most attacks aimed at the US.

Nobelium, a group connected to Russia, has historically targeted organizations, non-governmental organizations, think tanks, military, IT service providers, health technology and research, and telecommunications providers. In this case, Microsoft reports at least a quarter of targets work with international development, humanitarian, and human rights work.

Its newest campaign leverages Constant Contact, a legitimate mass-mailing service used for email marketing. Due to a high volume of emails distributed in this campaign, automated email threat detection marked many of the malicious emails as spam. However, some automated detection systems may have effectively delivered them due to configuration and policy settings.

Microsoft reports the attackers were able to gain control of the USAID Constant Contact account, allowing them to send seemingly authentic emails from USAID to thousands of victims. There were many iterations in the May 25 campaign; in one example, emails appear to come from USAID but have an authentic sender email address that matches Constant Contact.

"Nobelium launched this week's attacks by gaining access to the Constant Contact account of USAID," wrote Tom Burt, corporate vice president for consumer security and trust at Microsoft, in a blog post. Burt noted Microsoft is in the process of notifying targeted customers and there is no indication these attacks use an exploit against, or flaw in, Microsoft products and services.

Use of Constant Contact allowed attackers to hide links behind the mailing service's URL. Officials note many emails and document service providers offer a tool to simplify link sharing and provide information into who clicks these links and when.

When clicked, the email's malicious link leads to delivery of an ISO file that contains a malicious LNK file, a malicious DLL file, and a legitimate lure referencing foreign threats to the 2020 US federal elections, Volexity researchers explain in a blog post on the threat published this week. Microsoft notes the DLL is a custom Cobalt Strike Beacon loader that it calls NativeZone.

If successfully deployed, these payloads let attackers remain persistent on compromised systems so they can move laterally, steal data, deploy additional malware, and infect other machines on the network.

"Microsoft security researchers assess that the Nobelium's spearphishing operations are recurring and have increased in frequency and scope," MSTIC wrote in a separate blog post sharing the details of this attack, as well as its evolution and mitigations. "It is anticipated that additional activity may be carried out by the group using an evolving set of tactics."

A Closer Look At Nobelium's Strategy
This active campaign is notable for a few reasons, Burt explained. When considered along with the SolarWinds attack, it's clear Nobelium aims to breach trusted technology providers and infect their customers.

"By piggybacking on software updates and now mass email providers, Nobelium increases the chances of collateral damage in espionage operations and undermines trust in the technology ecosystem," Burt wrote.

While different from the attack on SolarWinds, this campaign underscores the consistency of cyber espionage. SolarWinds was notable for its stealth and discipline, but loud and widespread spear-phishing attacks were once a "calling card" of SVR operators who launched noisy phishing campaigns, says John Hultquist, vice president of analysis for Mandiant Threat Intelligence, who adds these attacks by Russia's Foreign Intelligence Service often effectively gained access to major government offices and other targets.

"And while the spear-phishing emails were quickly identified, we expect that any post-compromise actions by these actors would be highly skilled and stealthy," he points out. This newly identified campaign seems to have ramped up as the supply chain attacks were winding down, a sign these threats aren't going away any time soon.

"Given the brazen nature of this incident," Hultquist says, "it does not appear the SVR is prepared to throttle down on their cyberespionage activity."