Researchers have detailed a previously undocumented .NET-based post-exploitation framework called IceApple that has been deployed on Microsoft Exchange server instances to facilitate reconnaissance and data exfiltration.

"Suspected to be the work of a state-nexus adversary, IceApple remains under active development, with 18 modules observed in use across a number of enterprise environments, as of May 2022," CrowdStrike said in a Wednesday report.

The cybersecurity firm, which discovered the sophisticated malware in late 2021, noted its presence in multiple victim networks and in geographically distinct locations. Targeted victims span a wide range of sectors, including technology, academic, and government entities.

A post-exploitation toolset, as the name implies, is not used to provide initial access, but is rather employed to carry out follow-on attacks after having already compromised the hosts in question.

IceApple is notable for the fact that it's an in-memory framework, indicating an attempt on the part of the threat actor to maintain a low forensic footprint and evade detection, which, in turn, bears all hallmarks of a long-term intelligence-gathering mission.

While intrusions observed so far have involved the malware being loaded on Microsoft Exchange Servers, IceApple is capable of running under any Internet Information Services (IIS) web application, making it a potent threat.

The different modules that come with the framework equip the malware to list and delete files and directories, write data, steal credentials, query Active Directory, and export sensitive data. Build timestamps on these components date back to May 2021.

"At its core, IceApple is a post-exploitation framework focused on increasing an adversary's visibility of a target through acquisition of credentials and exfiltration of data," the researchers concluded.

"IceApple has been developed by an adversary with detailed knowledge of the inner workings of IIS. Ensuring all web applications are regularly and fully patched is critical to preventing IceApple from ending up in your environment."