CWE - CWE-1242: Inclusion of Undocumented Features or Chicken Bits (4.16)

Weakness ID: 1242

Vulnerability Mapping: ALLOWED This CWE ID may be used to map to real-world vulnerabilities
Abstraction: Base Base - 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 device includes chicken bits or undocumented features that can create entry points for unauthorized actors.

Extended Description

A common design practice is to use undocumented bits on a device that can be used to disable certain functional security features. These bits are commonly referred to as "chicken bits". They can facilitate quick identification and isolation of faulty components, features that negatively affect performance, or features that do not provide the required controllability for debug and test. Another way to achieve this is through implementation of undocumented features. An attacker might exploit these interfaces for unauthorized access.

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.

Scope	Impact	Likelihood
Confidentiality Integrity Availability Access Control	Technical Impact: Modify Memory; Read Memory; Execute Unauthorized Code or Commands; Gain Privileges or Assume Identity; Bypass Protection Mechanism

Potential Mitigations

Phases: Architecture and Design; Implementation

The implementation of chicken bits in a released product is highly discouraged. If implemented at all, ensure that they are disabled in production devices. All interfaces to a device should be documented.

Effectiveness: High

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" (CWE-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.	284	Improper Access Control

Relevant to the view "Hardware Design" (CWE-1194)

Nature	Type	ID	Name
MemberOf	Category - a CWE entry that contains a set of other entries that share a common characteristic.	1198	Privilege Separation and Access Control Issues

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.

Phase	Note
Architecture and Design
Implementation
Documentation

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: Not Technology-Specific (Undetermined Prevalence)

Class: ICS/OT (Undetermined Prevalence)

Demonstrative Examples

Example 1

Consider a device that comes with various security measures, such as secure boot. The secure-boot process performs firmware-integrity verification at boot time, and this code is stored in a separate SPI-flash device. However, this code contains undocumented "special access features" intended to be used only for performing failure analysis and intended to only be unlocked by the device designer.

(bad code)

Example Language: Other

Attackers dump the code from the device and then perform reverse engineering to analyze the code. The undocumented, special-access features are identified, and attackers can activate them by sending specific commands via UART before secure-boot phase completes. Using these hidden features, attackers can perform reads and writes to memory via the UART interface. At runtime, the attackers can also execute arbitrary code and dump the entire memory contents.

Remove all chicken bits and hidden features that are exposed to attackers. Add authorization schemes that rely on cryptographic primitives to access any features that the manufacturer does not want to expose. Clearly document all interfaces.

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.	1371	ICS Supply Chain: Poorly Documented or Undocumented Features
MemberOf	Category - a CWE entry that contains a set of other entries that share a common characteristic.	1396	Comprehensive Categorization: Access Control

Vulnerability Mapping Notes

Usage: ALLOWED

(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.

Taxonomy Mappings

Mapped Taxonomy Name	Node ID	Mapped Node Name
ISA/IEC 62443	Part 4-1	Req SD-4
ISA/IEC 62443	Part 4-1	Req SVV-3
ISA/IEC 62443	Part 4-2	Req CR 2.12

Related Attack Patterns

CAPEC-ID	Attack Pattern Name
CAPEC-212	Functionality Misuse
CAPEC-36	Using Unpublished Interfaces or Functionality

References

[REF-1071] Ali Abbasi, Tobias Scharnowski and Thorsten Holz. "Doors of Durin: The Veiled Gate to Siemens S7 Silicon". <https://i.blackhat.com/eu-19/Wednesday/eu-19-Abbasi-Doors-Of-Durin-The-Veiled-Gate-To-Siemens-S7-Silicon.pdf>.

[REF-1072] Sergei Skorobogatov and Christopher Woods. "Breakthrough Silicon Scanning Discovers Backdoor in Military Chip". <https://www.cl.cam.ac.uk/~sps32/Silicon_scan_draft.pdf>.

[REF-1073] Chris Domas. "God Mode Unlocked: Hardware Backdoors in x86 CPUs". <https://i.blackhat.com/us-18/Thu-August-9/us-18-Domas-God-Mode-Unlocked-Hardware-Backdoors-In-x86-CPUs.pdf>.

[REF-1074] Jonathan Brossard. "Hardware Backdooring is Practical". <https://media.blackhat.com/bh-us-12/Briefings/Brossard/BH_US_12_Brossard_Backdoor_Hacking_Slides.pdf>.

[REF-1075] Sergei Skorabogatov. "Security, Reliability, and Backdoors". <https://www.cl.cam.ac.uk/~sps32/SG_talk_SRB.pdf>.

Content History

Submissions
Submission Date	Submitter	Organization
2020-02-13 (CWE 4.0, 2020-02-24)	Arun Kanuparthi, Hareesh Khattri, Parbati Kumar Manna, Narasimha Kumar V Mangipudi	Intel Corporation
2020-02-13 (CWE 4.0, 2020-02-24)
Contributions
Contribution Date	Contributor	Organization
2023-04-25	"Mapping CWE to 62443" Sub-Working Group	CWE-CAPEC ICS/OT SIG
2023-04-25	Suggested mappings to ISA/IEC 62443.
Modifications
Modification Date	Modifier	Organization
2020-08-20	CWE Content Team	MITRE
2020-08-20	updated Applicable_Platforms, Demonstrative_Examples, Description, Potential_Mitigations, Related_Attack_Patterns
2022-04-28	CWE Content Team	MITRE
2022-04-28	updated Relationships
2023-01-31	CWE Content Team	MITRE
2023-01-31	updated Applicable_Platforms
2023-04-27	CWE Content Team	MITRE
2023-04-27	updated Relationships, Taxonomy_Mappings
2023-06-29	CWE Content Team	MITRE
2023-06-29	updated Mapping_Notes, Taxonomy_Mappings
2024-02-29 (CWE 4.14, 2024-02-29)	CWE Content Team	MITRE
2024-02-29 (CWE 4.14, 2024-02-29)	updated Taxonomy_Mappings


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Common Weakness Enumeration

CWE-1242: Inclusion of Undocumented Features or Chicken Bits

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