MosaicRegressor: Lurking in the Shadows of UEFI

UEFI (or Unified Extensible Firmware Interface) has become a prominent technology that is embedded within designated chips on modern day computer systems. Replacing the legacy BIOS, it is typically used to facilitate the machine’s boot sequence and load the operating system, while using a feature-rich environment to do so. At the same time, it has become the target of threat actors to carry out exceptionally persistent attacks.

One such attack has become the subject of our research, where we found a compromised UEFI firmware image that contained a malicious implant. This implant served as means to deploy additional malware on the victim computers, one that we haven’t come across thus far. To the best of our knowledge, this is the second known public case where malicious UEFI firmware in use by a threat actor was found in the wild.

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Source: Kaspersky