MZ Automation libiec61850 Out-of-bounds Read

The MMS server connection handler contains a flaw in its processing of
BER-encoded request data. When an MMS confirmed request PDU containing
an extended BER tag is received over an established session, the decoder
may advance its internal buffer incorrectly due to a missing bounds
check. This results in a one byte heap out-of-bounds read and causes the
MMS service process to terminate, leading to a denial-of-service
condition.