Vulnerability Mapping:ALLOWEDThis CWE ID may be used to map to real-world vulnerabilities Abstraction:
BaseBase - a weakness that is still mostly independent of a resource or technology, but with sufficient details to provide specific methods for detection and prevention. Base level weaknesses typically describe issues in terms of 2 or 3 of the following dimensions: behavior, property, technology, language, and resource.
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Description
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.
Extended Description
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.
Common Consequences
This table specifies different individual consequences
associated with the weakness. The Scope identifies the application security area that is
violated, while the Impact describes the negative technical impact that arises if an
adversary succeeds in exploiting this weakness. The Likelihood provides information about
how likely the specific consequence is expected to be seen relative to the other
consequences in the list. For example, there may be high likelihood that a weakness will be
exploited to achieve a certain impact, but a low likelihood that it will be exploited to
achieve a different impact.
This type of weakness all depends on the capabilities of the logic being controlled or configured by the reserved bits.
Potential Mitigations
Phase(s)
Mitigation
Architecture and Design; Implementation
Include a feature to disable reserved bits.
Integration
Any writes to these reserve bits are blocked (e.g., ignored, access-protected, etc.), or an exception can be asserted.
Relationships
This table shows the weaknesses and high level categories that are related to this
weakness. These relationships are defined as ChildOf, ParentOf, MemberOf and give insight to
similar items that may exist at higher and lower levels of abstraction. In addition,
relationships such as PeerOf and CanAlsoBe are defined to show similar weaknesses that the user
may want to explore.
Relevant to the view "Research Concepts" (View-1000)
Nature
Type
ID
Name
ChildOf
Pillar - a weakness that is the most abstract type of weakness and represents a theme for all class/base/variant weaknesses related to it. A Pillar is different from a Category as a Pillar is still technically a type of weakness that describes a mistake, while a Category represents a common characteristic used to group related things.
The different Modes of Introduction provide information
about how and when this
weakness may be introduced. The Phase identifies a point in the life cycle at which
introduction
may occur, while the Note provides a typical scenario related to introduction during the
given
phase.
Phase
Note
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
This listing shows possible areas for which the given
weakness could appear. These
may be for specific named Languages, Operating Systems, Architectures, Paradigms,
Technologies,
or a class of such platforms. The platform is listed along with how frequently the given
weakness appears for that instance.
Languages
Class: Not Language-Specific
(Undetermined Prevalence)
Operating Systems
Class: Not OS-Specific
(Undetermined Prevalence)
Architectures
Class: Not Architecture-Specific
(Undetermined Prevalence)
Technologies
Class: System on Chip
(Undetermined Prevalence)
Demonstrative Examples
Example 1
Assume a hardware Intellectual Property (IP) has address space 0x0-0x0F for its configuration registers, with the last one labeled reserved (i.e. 0x0F). Therefore inside the Finite State Machine (FSM), the code is as follows:
(bad code)
Example Language: Verilog
reg gpio_out = 0; //gpio should remain low for normal operation
case (register_address)
4'b1111 : //0x0F
begin
gpio_out = 1;
end
An adversary may perform writes to reserved address space in hopes of changing the behavior of the hardware. In the code above, the GPIO pin should remain low for normal operation. However, it can be asserted by accessing the reserved address space (0x0F). This may be a concern if the GPIO state is being used as an indicator of health (e.g. if asserted the hardware may respond by shutting down or resetting the system, which may not be the correct action the system should perform).
In the code below, the condition "register_address = 0X0F" is commented out, and a default is provided that will catch any values of register_address not explicitly accounted for and take no action with regards to gpio_out. This means that an attacker who is able to write 0X0F to register_address will not enable any undocumented "features" in the process.
(good code)
Example Language: Verilog
reg gpio_out = 0; //gpio should remain low for normal operation
case (register_address)
//4'b1111 : //0x0F
default: gpio_out = gpio_out;
Weakness Ordinalities
Ordinality
Description
Primary
(where the weakness exists independent of other weaknesses)
Memberships
This MemberOf Relationships table shows additional CWE Categories and Views that
reference this weakness as a member. This information is often useful in understanding where a
weakness fits within the context of external information sources.
Nature
Type
ID
Name
MemberOf
Category - a CWE entry that contains a set of other entries that share a common characteristic.
(this CWE ID may be used to map to real-world vulnerabilities)
Reason
Acceptable-Use
Rationale
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.
Comments
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.
Description
This table specifies different individual consequences
associated with the weakness. The Scope identifies the application security area that is
violated, while the Impact describes the negative technical impact that arises if an
adversary succeeds in exploiting this weakness. The Likelihood provides information about
how likely the specific consequence is expected to be seen relative to the other
consequences in the list. For example, there may be high likelihood that a weakness will be
exploited to achieve a certain impact, but a low likelihood that it will be exploited to
achieve a different impact.
