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Microsoft Details FoggyWeb Backdoor Used by SolarWinds Hackers

Microsoft on Monday published a blog post detailing a piece of malware used by the threat actor behind the SolarWinds attack to exfiltrate data from compromised servers.

The Russia-linked threat group that breached the systems of Texas-based IT management solutions provider SolarWinds is tracked by Microsoft as Nobelium. The tech giant has detailed several pieces of malware used by the hackers in their attacks and on Monday it shared an in-depth analysis of a backdoor it has named FoggyWeb.

Microsoft says FoggyWeb has been used in attacks since at least April 2021. The company has notified customers whose systems have been targeted or compromised as part of attacks involving this malware.

FoggyWeb has been described by Microsoft as a post-exploitation passive backdoor that the hackers have been using to remotely exfiltrate sensitive information from compromised Active Directory Federation Services (AD FS) servers. The backdoor, the company says, is persistent and highly targeted.

“Once NOBELIUM obtains credentials and successfully compromises a server, the actor relies on that access to maintain persistence and deepen its infiltration using sophisticated malware and tools,” Microsoft explained. “NOBELIUM uses FoggyWeb to remotely exfiltrate the configuration database of compromised AD FS servers, decrypted token-signing certificate, and token-decryption certificate, as well as to download and execute additional components.”

In addition to technical details about the malware and how it’s deployed, Microsoft has shared indicators of compromise (IOC) for FoggyWeb, as well as recommendations for detecting and mitigating the threat.

Nobelium has continued to launch attacks even after its operations were exposed following the discovery of the SolarWinds breach. In June, Microsoft warned that the hackers had continued to conduct operations aimed at IT companies, with targets identified across 36 countries.

In the SolarWinds attack, the hackers delivered their first-stage malware to thousands of organizations, but they actually hacked into the systems of only roughly 100 SolarWinds customers.

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Related: Poisoned Installers Found in SolarWinds Hackers Toolkit

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Eduard Kovacs (@EduardKovacs) is a contributing editor at SecurityWeek. He worked as a high school IT teacher for two years before starting a career in journalism as Softpedia’s security news reporter. Eduard holds a bachelor’s degree in industrial informatics and a master’s degree in computer techniques applied in electrical engineering.