CWE-1209 Detail

The reserved bits in a hardware design are not disabled prior to production. Typically, reserved bits are used for future capabilities and should not support any functional logic in the design. However, designers might covertly use these bits to debug or further develop new capabilities in production hardware. Adversaries with access to these bits will write to them in hopes of compromising hardware state.

Reserved bits are labeled as such so they can be allocated for a later purpose. They are not to do anything in the current design. However, designers might want to use these bits to debug or control/configure a future capability to help minimize time to market (TTM). If the logic being controlled by these bits is still enabled in production, an adversary could use the logic to induce unwanted/unsupported behavior in the hardware.

Modes Of Introduction

Architecture and Design : The Designer and Implementer have to make a conscious choice to do this
Implementation : The Designer and Implementer have to make a conscious choice to do this
Documentation : If documentation labels anything "for future use", "reserved", or the like, such labeling could indicate to an attacker a potential attack point

Applicable Platforms

Language

Class: Not Language-Specific (Undetermined)

Operating Systems

Class: Not OS-Specific (Undetermined)

Architectures

Class: Not Architecture-Specific (Undetermined)

Technologies

Class: System on Chip (Undetermined)

Common Consequences

Potential Mitigations

Phases : Architecture and Design // Implementation

Include a feature to disable reserved bits.

Phases : Integration

Any writes to these reserve bits are blocked (e.g., ignored, access-protected, etc.), or an exception can be asserted.

Vulnerability Mapping Notes

Justification : This CWE entry is at the Base level of abstraction, which is a preferred level of abstraction for mapping to the root causes of vulnerabilities.
Comment : Carefully read both the name and description to ensure that this mapping is an appropriate fit. Do not try to 'force' a mapping to a lower-level Base/Variant simply to comply with this preferred level of abstraction.

Related Attack Patterns

Submission

Modifications