Various ranges can be defined in the system-address map, either in the memory or in Memory-Mapped-IO (MMIO) space. These ranges are usually defined using special range registers that contain information, such as base address and size. Address decoding is the process of determining for which range the incoming transaction is destined.

To ensure isolation, ranges containing secret data are access-control protected. Occasionally, these ranges could overlap. The overlap could either be intentional (e.g. due to a limited number of range registers or limited choice in choosing size of the range) or unintentional (e.g. introduced by errors).

Some hardware designs allow dynamic remapping of address ranges assigned to peripheral MMIO ranges. In such designs, intentional address overlaps can be created through misconfiguration by malicious software. When protected and unprotected ranges overlap, an attacker could send a transaction and potentially compromise the protections in place, violating the principle of least privilege.