A vulnerability exists in the HCI IEC 60870-5-104 function included in certain versions of the RTU500 series product. The vulnerability can only be exploited, if the HCI 60870-5-104 is configured with support for IEC 62351-5 and the CMU contains the license feature ‘Advanced security’ which must be ordered separately. If these preconditions are fulfilled, an attacker could exploit the vulnerability by sending a specially crafted message to the RTU500, causing the targeted RTU500 CMU to reboot. The vulnerability is caused by a missing input data validation which eventually if exploited causes an internal buffer to overflow in the HCI IEC 60870-5-104 function.