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CWE-1191: Exposed Chip Debug Interface With Insufficient Access Control

Weakness ID: 1191
Abstraction: Base
Structure: Simple
Status: Draft
Presentation Filter:
+ Description
The chip does not implement or does not correctly enforce access control on the debug interface, thus allowing an attacker to exercise the debug interface to access a portion of the chip internal registers that typically would not be exposed.
+ Extended Description

Integrated circuits can expose the chip internals through a scan chain interconnected through internal registers etc., through scan flip-flops. A Joint Test Action Group (JTAG) compatible test access port usually provides access to this scan chain for debugging the chip. Since almost every asset in the chip can be accessed over this debug interface, chip manufacturers typically insert some form of password-based or challenge-response based access control mechanisms to prevent misuse. This mechanism is implemented in addition to on-chip protections that are already present. If this debug access control is not implemented or the access control check is not implemented properly, or if the hardware does not clear secret keys, etc., when debug more is entered, an attacker may be able to bypass on-chip access control mechanisms through debug features/interfaces.

+ 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)
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
+ Relevant to the view "Hardware Design" (CWE-1194)
MemberOfCategoryCategory - a CWE entry that contains a set of other entries that share a common characteristic.1207Debug and Test Problems
+ 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.

Architecture and Design
+ 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.


Class: Language-Independent (Undetermined Prevalence)


Class: System on Chip (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.

Access Control

Technical Impact: Bypass Protection Mechanism

+ Observed Examples
chain: JTAG interface is not disabled (CWE-1191) during ROM code execution, introducing a race condition (CWE-362) to extract encryption keys
+ Potential Mitigations

Phase: Architecture and Design

Strategy: Separation of Privilege

Implement an access control mechanism to exercise the debug interface in order to control and observe security-sensitive chip internals.

Password checking logic should be resistant to timing attacks. Security-sensitive data stored in registers, such as keys, etc. should be cleared when entering debug mode.

+ References
[REF-1037] Kurt Rosenfeld and Ramesh Karri. "Attacks and Defenses for JTAG". 2010-02. <>.
[REF-1043] Gopal Vishwakarma and Wonjun Lee. "Exploiting JTAG and Its Mitigation in IOT: A Survey". 2018-12-03. <>.
+ Content History
Submission DateSubmitterOrganization
2019-10-15Intel Corporation
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Page Last Updated: February 19, 2020