Microsoft has revealed new malware from the hacking group behind the SolarWinds supply chain attack last December, delivering additional payloads and stealing sensitive information from Active Directory Federation Services servers. Codenamed “FoggyWeb”, it is described as a “passive and highly targeted backdoor”. They stated they first observed FoggyWeb in the wild as early as April 2021, describing the implant as a “malicious memory-resident DLL.”

Nobelium is the moniker assigned by Microsoft to the nation-state hacking group widely known as APT29, The Dukes, or Cozy Bear, an advanced persistent threat that has been attributed to Russia’s Foreign Intelligence Service (SVR).

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. The APT group utilises FoggyWeb to remotely exfiltrate the configuration database of compromised AD FS servers, decrypted token-signing certificate, and token-decryption certificate and to download and execute additional components.

FoggyWeb, installed using a loader by exploiting a technique called DLL search order hijacking, is capable of transmitting sensitive information from a compromised AD FS server and receiving and executing additional malicious payloads retrieved from a remote attacker-controlled server. It’s also engineered to monitor all incoming HTTP GET and POST requests sent to the server from the intranet (or internet) and intercept HTTP requests that are of interest to the actor.

In terms of mitigation, protecting AD FS servers is key to mitigating Nobelium attacks. Detecting and blocking malware, attacker activity, and other malicious artefacts on AD FS servers can break critical steps in known Nobelium attack chains. This can be fulfilled by following Microsoft’s best practices for securing Active Directory Federation Services, in addition to endpoint detection and response tooling and alerting.

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