CWE

Common Weakness Enumeration

A Community-Developed List of Software & Hardware Weakness Types

CWE Top 25 Most Dangerous Software Errors
Home > CWE List > CWE- Individual Dictionary Definition (4.0)  
ID

CWE-1221: Incorrect Register Defaults or Module Parameters

Weakness ID: 1221
Abstraction: Base
Structure: Simple
Status: Incomplete
Presentation Filter:
+ Description
Hardware description language code incorrectly defines register defaults or hardware IP parameters to insecure values.
+ Extended Description

Integrated circuits and hardware IP software programmable controls and settings are commonly stored in register circuits. These register contents have to be initialized at hardware reset to defined default values that are hard coded in the hardware description language (HDL) code of the hardware unit. Hardware descriptive languages also support definition of parameter variables, which can be defined in code during instantiation of the hardware IP module. Such parameters are generally used to configure a specific instance of a hardware IP in the design.

The system security settings of a hardware design can be affected by incorrectly defined default values or IP parameters. The hardware IP would be in an insecure state at power reset, and this can be exposed or exploited by untrusted software running on the system. Both register defaults and parameters are hardcoded values, which cannot be changed using software or firmware patches but must be changed in hardware silicon. Thus, such security issues are considerably more difficult to address later in the lifecycle. Hardware designs can have a large number of such parameters and register defaults settings, and it is important to have design tool support to check these settings in an automated way and be able to identify which settings are security sensitive.

+ Relationships

The table(s) below 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" (CWE-1000)
NatureTypeIDName
ChildOfClassClass - a weakness that is described in a very abstract fashion, typically independent of any specific language or technology. More specific than a Pillar Weakness, but more general than a Base Weakness. Class level weaknesses typically describe issues in terms of 1 or 2 of the following dimensions: behavior, property, and resource.665Improper Initialization
+ Relevant to the view "Hardware Design" (CWE-1194)
NatureTypeIDName
MemberOfCategoryCategory - a CWE entry that contains a set of other entries that share a common characteristic.1199General Circuit and Logic Design Concerns
+ Modes Of Introduction

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.

PhaseNote
ImplementationSuch issues could be introduced during implementation of hardware design, since IP parameters and defaults are defined in HDL code and identified later during Testing or System Configuration phases.
+ Applicable Platforms
The listings below show 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

Verilog (Undetermined Prevalence)

VHDL (Undetermined Prevalence)

Technologies

Class: Technology-Independent (Undetermined Prevalence)

+ Common Consequences

The table below 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.

ScopeImpactLikelihood
Confidentiality
Integrity
Availability
Access Control

Technical Impact: Varies by Context

Degradation of system functionality, or loss of access control enforcement
+ Demonstrative Examples

Example 1

Consider example design module system verilog code shown below.register_example module is an example parameterized module that defines two parameters, REGISTER_WIDTH and REGISTER_DEFAULT. Register_example module defines a Secure_mode setting, which when set makes the register content read-only and not modifiable by software writes. register_top module instantiates two registers, Insecure_Device_ID_1 and Insecure_Device_ID_2. Generally, registers containing device identifier values are required to be read only to prevent any possibility of software modifying these values.

(bad code)
Example Language: Verilog 
// Parameterized Register module example
// Secure_mode : REGISTER_DEFAULT[0] : When set to 1 register is read only and not writable//
/module register_example
s#(
parameter REGISTER_WIDTH = 8, // Parameter defines width of register, default 8 bits
parameter [REGISTER_WIDTH-1:0] REGISTER_DEFAULT = 2**REGISTER_WIDTH -2 // Default value of register computed from Width. Sets all bits to 1s except bit 0 (Secure _mode)
)
(
input [REGISTER_WIDTH-1:0] Data_in,
input Clk,
input resetn,
input write,
output reg [REGISTER_WIDTH-1:0] Data_out
);

reg Secure_mode;

always @(posedge Clk or negedge resetn)
if (~resetn)
begin
Data_out <= REGISTER_DEFAULT; // Register content set to Default at reset
Secure_mode <= REGISTER_DEFAULT[0]; // Register Secure_mode set at reset
end
else if (write & ~Secure_mode)
begin
Data_out <= Data_in;
end
endmodule


module register_top
(
input Clk,
input resetn,
input write,
input [31:0] Data_in,
output reg [31:0] Secure_reg,
output reg [31:0] Insecure_reg
);

register_example #(
.REGISTER_WIDTH (32),
.REGISTER_DEFAULT (1224) // Incorrect Default value used bit 0 is 0.
) Insecure_Device_ID_1 (
.Data_in (Data_in),
.Data_out (Secure_reg),
.Clk (Clk),
.resetn (resetn),
.write (write)
);

register_example #(
.REGISTER_WIDTH (32) // Default not defined 2^32-2 value will be used as default.
) Insecure_Device_ID_2 (
.Data_in (Data_in),
.Data_out (Insecure_reg),
.Clk (Clk),
.resetn (resetn),
.write (write)
);

endmodule

These example instantiations show how, in a hardware design, it would be possible to instantiate the register module with insecure defaults and parameters.

In the example design, both registers will be software writable since Secure_mode is defined as zero.

(informative)
 
register_example #(
.REGISTER_WIDTH (32),
.REGISTER_DEFAULT (1225) // Correct default value set, to enable Secure_mode
) Secure_Device_ID_example (
.Data_in (Data_in),
.Data_out (Secure_reg),
.Clk (Clk),
.resetn (resetn),
.write (write)
);
+ Potential Mitigations

Phase: Architecture and Design

During hardware design all the system parameters and register defaults must be reviewed to identify security sensitive settings

Phase: Implementation

The default values of these security sensitive settings need to be defined as part of the design review phase.

Phase: Testing

Testing phase should use automated tools to test that values are configured per design specifications.
+ Content History
Submissions
Submission DateSubmitterOrganization
2019-12-12Hareesh KhattriIntel Corporation
More information is available — Please select a different filter.
Page Last Updated: February 19, 2020