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CWE-1290: Incorrect Decoding of Security Identifiers

Weakness ID: 1290
Abstraction: Base
Structure: Simple
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+ Description
The product implements a decoding mechanism to decode certain bus-transaction signals to security identifiers. If the decoding is implemented incorrectly, then untrusted agents can now gain unauthorized access to the asset.
+ Extended Description

In a System-On-Chip (SoC), various integrated circuits and hardware engines generate transactions such as to access (reads/writes) assets or perform certain actions (e.g., reset, fetch, compute, etc.). Among various types of message information, a typical transaction is comprised of source identity (to identify the originator of the transaction) and a destination identity (to route the transaction to the respective entity). Sometimes the transactions are qualified with a security identifier. The security identifier helps the destination agent decide on the set of allowed actions (e.g., access an asset for read and writes). A decoder decodes the bus transactions to map security identifiers into necessary access-controls/protections.

A common weakness that can exist in this scenario is incorrect decoding because an untrusted agent's security identifier is decoded into a trusted agent's security identifier. Thus, an untrusted agent previously without access to an asset can now gain access to the asset.

+ Relationships
Section HelpThis 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" (CWE-1000)
ChildOfPillarPillar - 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.284Improper Access Control
Section HelpThis 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 "Hardware Design" (CWE-1194)
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.1294Insecure Security Identifier Mechanism
+ Modes Of Introduction
Section HelpThe 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.
Architecture and Design
+ Applicable Platforms
Section HelpThis 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.


Class: Not Language-Specific (Undetermined Prevalence)

Operating Systems

Class: Not OS-Specific (Undetermined Prevalence)


Class: Not Architecture-Specific (Undetermined Prevalence)


Bus/Interface Hardware (Undetermined Prevalence)

Class: Not Technology-Specific (Undetermined Prevalence)

+ Common Consequences
Section HelpThis 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.
Access Control

Technical Impact: Modify Memory; Read Memory; DoS: Resource Consumption (Other); Execute Unauthorized Code or Commands; Gain Privileges or Assume Identity; Quality Degradation

+ Demonstrative Examples

Example 1

Consider a system that has four bus masters and a decoder. The decoder is supposed to decode every bus transaction and assign a corresponding security identifier. The security identifier is used to determine accesses to the assets. The bus transaction that contains the security information is Bus_transaction [15:14], and the bits 15 through 14 contain the security identifier information. The table below provides bus masters as well as their security identifiers and trust assumptions:

Bus MasterSecurity Identifier DecodingTrust Assumptions

The assets are the AES-Key registers for encryption or decryption. The key is 128 bits implemented as a set of four 32-bit registers. The AES_KEY_ACCESS_POLICY is used to define which agents with a security identifier in the transaction can access the AES-key registers. The size of the security identifier is 4 bits (i.e., bit 3 through 0). Each bit in these 4 bits defines a security identifier. There are only 4 security identifiers that are allowed accesses to the AES-key registers. The number of the bit when set (i.e., "1") allows respective action from an agent whose identity matches the number of the bit. If clear (i.e., "0"), disallows the respective action to that corresponding agent.

RegisterField description
AES_ENC_DEC_KEY_0AES key [0:31] for encryption or decryption
Default 0x00000000
AES_ENC_DEC_KEY_1AES key [32:63] for encryption or decryption
Default 0x00000000
AES_ENC_DEC_KEY_2AES key [64:95] for encryption or decryption
Default 0x00000000
AES_ENC_DEC_KEY_3AES key [96:127] for encryption or decryption
Default 0x00000000
AES_KEY_ACCESS_POLCY[31:4] Default 0x00000000
[3:0]-0x01 agent with Security Identified "1" has access to AES_ENC_DEC_KEY_0 through AES_ENC_DEC_KEY_3 registers

The following Pseudo code outlines the process of checking the value of the Security Identifier within the AES_KEY_ACCESS_POLICY register:

Example Language: Other 

If (AES_KEY_ACCESS_POLICY[Security_Identifier] == "1")
Allow access to AES-Key registers

Deny access to AES-Key registers

Below is a decoder's Pseudo code that only checks for bit [14] of the bus transaction to determine what Security Identifier it must assign.

(bad code)
Example Language: Other 

If (Bus_transaction[14] == "1")
Security_Identifier == "1"

Security_Identifier == "0"

The security identifier is two bits, but the decoder code above only checks the value of one bit. Two Masters have their bit 0 set to "1" - Master_1 and Master_3. Master_1 is trusted, while Master_3 is not. The code above would therefore allow an untrusted agent, Master_3, access to the AES-Key registers in addition to intended trusted Master_1.
The decoder should check for the entire size of the security identifier in the bus-transaction signal to assign a corresponding security identifier. The following is good Pseudo code:

(good code)
Example Language: Other 

If (Bus_transaction[15:14] == "00")
Security_Identifier == "0"

If (Bus_transaction[15:14] == "01")
Security_Identifier == "1"

If (Bus_transaction[15:14] == "10")
Security_Identifier == "2"

If (Bus_transaction[15:14] == "11")
Security_Identifier == "3"
+ Potential Mitigations

Phase: Architecture and Design

Security identifier decoders must be reviewed for design consistency and common weaknesses.

Phase: Implementation

Access and programming flows must be tested in pre-silicon and post-silicon testing in order to check for this weakness.
+ Memberships
Section HelpThis 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.
MemberOfCategoryCategory - a CWE entry that contains a set of other entries that share a common characteristic.1396Comprehensive Categorization: Access Control
+ Vulnerability Mapping Notes

Usage: Allowed

(this CWE ID could be used to map to real-world vulnerabilities)

Reason: Acceptable-Use


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.


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.
+ Content History
+ Submissions
Submission DateSubmitterOrganization
(CWE 4.2, 2020-08-20)
Arun Kanuparthi, Hareesh Khattri, Parbati Kumar MannaIntel Corporation
+ Modifications
Modification DateModifierOrganization
2021-07-20CWE Content TeamMITRE
updated Related_Attack_Patterns
2021-10-28CWE Content TeamMITRE
updated Demonstrative_Examples
2022-04-28CWE Content TeamMITRE
updated Applicable_Platforms
2022-06-28CWE Content TeamMITRE
updated Applicable_Platforms
2022-10-13CWE Content TeamMITRE
updated Demonstrative_Examples, Related_Attack_Patterns
2023-01-31CWE Content TeamMITRE
updated Demonstrative_Examples
2023-04-27CWE Content TeamMITRE
updated Relationships
2023-06-29CWE Content TeamMITRE
updated Mapping_Notes
Page Last Updated: October 26, 2023