GRIMBOLT

According to Mandiant, GRIMBOLT is a C#-written foothold backdoor compiled using native ahead-of-time (AOT) compilation and packed with UPX. It provides a remote shell capability and uses the same command and control as previously deployed BRICKSTORM payload. It's unclear if the threat actor's replacement of BRICKSTORM with GRIMBOLT was part of a pre-planned life cycle iteration by the threat actor or a reaction to incident response.