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ID

CWE-1268: Policy Privileges are not Assigned Consistently Between Control and Data Agents

Weakness ID: 1268
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 product's hardware-enforced access control for a particular resource improperly accounts for privilege discrepancies between control and write policies.
+ Extended Description

Integrated circuits and hardware engines may provide access to resources (device-configuration, encryption keys, etc.) belonging to trusted firmware or software modules (commonly set by a BIOS or a bootloader). These accesses are typically controlled and limited by the hardware. Hardware design access control is sometimes implemented using a policy. A policy defines which entity or agent may or may not be allowed to perform an action. When a system implements multiple levels of policies, a control policy may allow direct access to a resource as well as changes to the policies themselves.

Resources that include agents in their control policy but not in their write policy could unintentionally allow an untrusted agent to insert itself in the write policy register. Inclusion in the write policy register could allow a malicious or misbehaving agent write access to resources. This action could result in security compromises including leaked information, leaked encryption keys, or modification of device configuration.

+ 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)
NatureTypeIDName
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)
NatureTypeIDName
MemberOfCategoryCategory - a CWE entry that contains a set of other entries that share a common characteristic.1198Privilege Separation and Access Control Issues
+ 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.
PhaseNote
Architecture and DesignThis weakness may be introduced during the design of a device when the architect does not comprehensively specify all of the policies required by an agent.
ImplementationThis weakness may be introduced during implementation if device policy restrictions do not sufficiently constrain less-privileged clients.
+ 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.

Languages

Class: Not Language-Specific (Undetermined Prevalence)

Operating Systems

Class: Not OS-Specific (Undetermined Prevalence)

Architectures

Class: Not Architecture-Specific (Undetermined Prevalence)

Technologies

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.
ScopeImpactLikelihood
Confidentiality
Integrity
Availability
Access Control

Technical Impact: Modify Memory; Read Memory; DoS: Crash, Exit, or Restart; Execute Unauthorized Code or Commands; Gain Privileges or Assume Identity; Bypass Protection Mechanism; Read Files or Directories; Reduce Reliability

High
+ Demonstrative Examples

Example 1

Consider a system of seven registers for storing and configuring an AES key for encryption or decryption.

Four 32-bit registers are used to store a 128-bit AES key. The names of those registers are AES_ENC_DEC_KEY_0, AES_ENC_DEC_KEY_1, AES_ENC_DEC_KEY_2, and AES_ENC_DEC_KEY_3. Collectively these are referred to as the AES Key registers.

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

Three 32-bit registers are used to define access control for the AES-key registers. The names of those registers are AES_KEY_CONTROL_POLICY, AES_KEY_READ_POLICY, and AES_KEY_WRITE_POLICY. Collectively these registers are referred to as the Policy registers, and their functions are explained next.

  • The AES_KEY_CONTROL_POLICY register defines which agents can write to the AES_KEY_READ_POLICY or AES_KEY_WRITE_POLICY registers.
  • The AES_KEY_READ_POLICY register defines which agents can read the AES-key registers.
  • The AES_KEY_WRITE_POLICY register defines which agents can write the AES key registers.

The preceding three policy registers encode access control at the bit level. Therefore a maximum of 32 agents can be defined (1 bit per agent). The value of the bit when set (i.e., "1") allows the respective action from an agent whose identity corresponds to the number of the bit. If clear (i.e., "0"), it disallows the respective action to that corresponding agent. For example, if bit 0 is set to "1" in the AES_KEY_READ_POLICY register, then agent 0 has permission to read the AES-key registers.

Consider that there are 4 agents named Agent 1, Agent 2, Agent 3, and Agent 4. For access control purposes Agent 1 is assigned to bit 1, Agent 2 to bit 2, Agent 3 to bit 3, and Agent 4 to bit 4. All agents are trusted except for Agent 3 who is untrusted. Also consider the register values in the below table.

(bad code)
 
RegisterField description
AES_KEY_CONTROL_POLICYControls which agents can write to READ_POLICY and WRITE_POLICY registers
[31:0] Default 0x00000018
AES_KEY_READ_POLICYControls which agents can read the AES-key registers
[31:0] Default 0x00000002
AES_KEY_WRITE_POLICYControls which agents can write to the AES-key registers
[31:0] Default 0x00000004

IThe AES_KEY_CONTROL_POLICY register value is 0x00000018. In binary, the lower 8 bits will be 0001 1000, meaning that:

  • Bits 3 and 4 are set, thus Agents 3 and 4 will have write access to AES_KEY_READ_POLICY or AES_KEY_WRITE_POLICY.
  • All other bits are clear, hence agents other than 3 and 4 will not have access to write to AES_KEY_READ_POLICY or AES_KEY_WRITE_POLICY.

The AES_KEY_READ_POLICY register value is 0x00000002. In binary, the lower 8 bits will be 0000 0010, meaning that:

  • Bit 1 is set, thus Agent 1 will be able to read the AES key registers.

The AES_KEY_WRITE_POLICY register value is 0x00000004. In binary, the lower 8 bits will be 0000 0100, meaning that:

  • Bit 2 is set, thus Agent 2 will be able to write the AES Key registers.

The configured access control policy for Agents 1,2,3,4 is summarized in table below.

AgentReadWriteControl
Agent 1AllowedNot AllowedNot Allowed
Agent 2Not AllowedAllowedNot Allowed
Agent 3Not AllowedNot AllowedAllowed
Agent 4Not AllowedNot AllowedAllowed

At this point Agents 3 and 4 can only configure which agents can read AES keys and which agents can write AES keys. Agents 3 and 4 cannot read or write AES keys - just configure access control.

Now, recall Agent 3 is untrusted. As explained above, the value of the AES_KEY_CONTROL_POLICY register gives agent 3 access to write to the AES_KEY_WRITE_POLICY register. Agent 3 can use this write access to add themselves to the AES_KEY_WRITE_POLICY register. This is accomplished by Agent 3 writing the value 0x00000006. In binary, the lower 8 bits are 0000 0110, meaning that bit 3 will be set. Thus, giving Agent 3 having the ability to write to the AES Key registers.

If the AES_KEY_CONTROL_POLICY register value is 0x00000010, the lower 8 bits will be 0001 0000. This will give Agent 4, a trusted agent, write access to AES_KEY_WRITE_POLICY, but Agent 3, who is untrusted, will not have write access. The Policy register values should therefore be as follows:

(good code)
 
RegisterField description
AES_KEY_CONTROL_POLICY[31:0] Default 0x00000010
AES_KEY_READ_POLICY[31:0] Default 0x00000002
AES_KEY_WRITE_POLICY[31:0] Default 0x00000004
+ Potential Mitigations

Phases: Architecture and Design; Implementation

Access-control-policy definition and programming flow must be sufficiently tested in pre-silicon and post-silicon testing.
+ 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.
NatureTypeIDName
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

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.
+ Notes

Maintenance

This entry is still under development and will continue to see updates and content improvements.
+ Content History
+ Submissions
Submission DateSubmitterOrganization
2020-02-12
(CWE 4.1, 2020-02-24)
Arun Kanuparthi, Hareesh Khattri, Parbati Kumar Manna, Narasimha Kumar V MangipudiIntel Corporation
+ Modifications
Modification DateModifierOrganization
2020-08-20CWE Content TeamMITRE
updated Demonstrative_Examples, Description, Modes_of_Introduction, Name, Potential_Mitigations, Related_Attack_Patterns
2021-10-28CWE Content TeamMITRE
updated Potential_Mitigations
2022-04-28CWE Content TeamMITRE
updated Related_Attack_Patterns
2022-10-13CWE Content TeamMITRE
updated Demonstrative_Examples
2023-01-31CWE Content TeamMITRE
updated Demonstrative_Examples
2023-04-27CWE Content TeamMITRE
updated Relationships
2023-06-29CWE Content TeamMITRE
updated Mapping_Notes
+ Previous Entry Names
Change DatePrevious Entry Name
2020-08-20Agents Included in Control Policy are not Contained in Less-Privileged Policy
Page Last Updated: February 29, 2024