Generally discussed herein are systems, apparatuses, and methods for secure transfer of content across a security boundary. A system can include a high side domain communicatively coupled to a transfer guard module, the high side domain comprising a high side data repository, a first review module executable by processing circuitry to determine whether a permission level of first content violates a permission level of the high side domain, a second review module executable by the processing circuitry to determine whether second content from the high side data repository includes a permission level that violates a permission level of a low side domain, a first data diode module communicatively coupled between the first review module and the high side data repository, and a second data diode module communicatively coupled between the second review module and the high side data repository.