Members of an advanced persistent threat (APT) group, masquerading as teleworking employees with legitimate credentials, accessed a US organization's network and planted a backdoor called Supernova on its SolarWinds Orion server for conducting reconnaissance, domain mapping, and data theft.

The attackers had access to the network for nearly one year, from March 2020 to February 2021, before they were discovered and blocked, the Department of Homeland Security's Cybersecurity and Infrastructure Security Agency (CISA) said Thursday in a report summarizing the findings of its investigation into the incident.

The report is the latest involving SolarWinds and its Orion network management server technology. However, the Supernova tool and the APT group behind it are separate from the group that used legitimate Orion software updates to distribute malware dubbed Sunburst to 18,000 organizations around the world. Last week the US government formally attributed that widely reported attack — described by many as one of the most sophisticated ever — to Russia's Foreign Intelligence Service, SVR.

CISA's malware analysis report, which includes indicators of compromise and mitigation recommendations, did not attribute the Supernova attack to any specific group or country. However, others such as Secureworks that have investigated similar intrusions lately have ascribed Supernova and its operators to Spiral, a believed China-based threat group. Only a small handful of organizations are known to have been infected with Supernova, so far at least.

In its report, CISA describes the incident as likely beginning last March when the attackers connected to the unnamed US entity's network via a Pulse Secure virtual private network (VPN) appliance. CISA's investigation showed the attackers used three residential IP addresses to access the VPN appliance. They authenticated to it using valid user accounts, none of which were protected by multifactor authentication. CISA said it has not been able to determine how the attackers obtained the credentials. The VPN access allowed the attackers to masquerade as legitimate remote employees of the organization.

Once the attackers gained initial access to the victim network, they moved laterally on it to the SolarWinds Orion server and installed Supernova, a .Net Web shell, on it. As was the case with the handful of other breaches involving Supernova, the attackers appear to have exploited an authentication bypass flaw (CVE-2020-10148) in SolarWinds Orion's API to execute a PowerShell script for running the Web shell.

"CISA believes the threat actor leveraged CVE-2020-10148 to bypass the authentication to the SolarWinds appliance and then used SolarWinds Orion API to run commands with the same privileges the SolarWinds appliance was running (in this case SYSTEM)," CISA explained.

Unlike the Sunburst backdoor associated with the Russia campaign, the attackers did not embed Supernova into the Orion technology. Instead, they installed the malware on servers running Orion by exploiting CVE-2020-10148. Once installed, the attackers used the Web shell to dump credentials from the SolarWinds server. Weeks later the adversary again connected via the VPN appliance and tried using the stolen credentials to access an additional workstation. On another occasion, the threat actor used Windows Management Instrumentation and other legitimate utilities to gather information about running process to collect, archive, and exfiltrate data.

Consistent With Other Attacks
Don Smith, senior director with Secureworks' counter threat unit, says the timing, tools, tactics, and procedures that CISA described this week are consistent with the company's own findings from its investigation of two intrusions at a customer location.

The report corroborates "our assessment that the two intrusions we responded to at the same organization were both perpetrated by the same threat actor, [(Spiral aka Bronze Spiral]," Smith says.

Those TTPs included initial access through exploitation of vulnerable Internet-facing systems, he says. It also includes "deployment of the Supernova Web shell, credential theft, ongoing access through VPN services using legitimate credentials, the deployment of other tools renamed to disguise their function, and the use of compromised infrastructure for command and control," Smith says.

The Supernova campaign was highly targeted and appears to have impacted only a very small number of organizations. However, it does serve as an example of how adversaries are constantly looking to exploit vulnerabilities they can exploit for initial access. Once established on a network, such threats can be hard to eliminate, Smith notes.

"We should also remember that it does not take long for other, more opportunistic threats like ransomware operators to seize on exploits once they become public and look to use them for their own gain, at which point any organization is a potential target," he says.