An issue was discovered in IhisiSmm in Insyde InsydeH2O with kernel 5.0 through 5.5. The IhisiDxe driver uses the command buffer to pass input and output data. By modifying the command buffer contents with DMA after the input parameters have been checked but before they are used, the IHISI SMM code may be convinced to modify SMRAM or OS, leading to possible data corruption or escalation of privileges.