CWE-1191 Detail

The chip does not implement or does not correctly perform access control to check whether users are authorized to access internal registers and test modes through the physical debug/test interface.

A device's internal information may be accessed through a scan chain of interconnected internal registers, usually through a JTAG interface. The JTAG interface provides access to these registers in a serial fashion in the form of a scan chain for the purposes of debugging programs running on a device. Since almost all information contained within a device may be accessed over this interface, device manufacturers typically insert some form of authentication and authorization to prevent unintended use of this sensitive information. This mechanism is implemented in addition to on-chip protections that are already present.

If authorization, authentication, or some other form of access control is not implemented or not implemented correctly, a user may be able to bypass on-chip protection mechanisms through the debug interface.

Sometimes, designers choose not to expose the debug pins on the motherboard. Instead, they choose to hide these pins in the intermediate layers of the board. This is primarily done to work around the lack of debug authorization inside the chip. In such a scenario (without debug authorization), when the debug interface is exposed, chip internals are accessible to an attacker.

Modes Of Introduction

Architecture and Design
Implementation

Applicable Platforms

Language

Class: Not Language-Specific (Undetermined)

Operating Systems

Class: Not OS-Specific (Undetermined)

Architectures

Class: Not Architecture-Specific (Undetermined)

Technologies

Class: Not Technology-Specific (Undetermined)

Common Consequences

Observed Examples

Potential Mitigations

Phases : Architecture and Design
If feasible, the manufacturer should disable the JTAG interface or implement authentication and authorization for the JTAG interface. If authentication logic is added, it should be resistant to timing attacks. Security-sensitive data stored in registers, such as keys, etc. should be cleared when entering debug mode.

Detection Methods

Dynamic Analysis with Manual Results Interpretation

Authentication and authorization of debug and test interfaces should be part of the architecture and design review process. Withholding of private register documentation from the debug and test interface public specification ("Security by obscurity") should not be considered as sufficient security.

Dynamic Analysis with Manual Results Interpretation

Dynamic tests should be done in the pre-silicon and post-silicon stages to verify that the debug and test interfaces are not open by default.

Fuzzing

Tests that fuzz Debug and Test Interfaces should ensure that no access without appropriate authentication and authorization is possible.
Effectiveness : Moderate

Vulnerability Mapping Notes

Justification : 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.
Comment : 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.

Related Attack Patterns

NotesNotes

CWE-1191 and CWE-1244 both involve physical debug access, but the weaknesses are different. CWE-1191 is effectively about missing authorization for a debug interface, i.e. JTAG. CWE-1244 is about providing internal assets with the wrong debug access level, exposing the asset to untrusted debug agents.

References

REF-1037

Attacks and Defenses for JTAG
Kurt Rosenfeld, Ramesh Karri.
https://ieeexplore.ieee.org/stamp/stamp.jsp?tp=&arnumber=5406671

REF-1043

Exploiting JTAG and Its Mitigation in IOT: A Survey
Gopal Vishwakarma, Wonjun Lee.
https://www.mdpi.com/1999-5903/10/12/121/pdf

REF-1084

JTAG Explained (finally!): Why "IoT", Software Security Engineers, and Manufacturers Should Care
Gopal Vishwakarma, Wonjun Lee.
https://www.mdpi.com/1999-5903/10/12/121/pdf

REF-1085

Design for Testability & Design for Debug
Bob Molyneaux, Mark McDermott, Anil Sabbavarapu.
http://users.ece.utexas.edu/~mcdermot/vlsi-2/Lecture_17.pdf

REF-1355

dmi_jtag.sv
Florian Zaruba.
https://github.com/HACK-EVENT/hackatdac21/blob/71103971e8204de6a61afc17d3653292517d32bf/piton/design/chip/tile/ariane/src/riscv-dbg/src/dmi_jtag.sv#L192:L204

REF-1354

Fix CWE-1191 in dmi_jtag.sv
Florian Zaruba.
https://github.com/HACK-EVENT/hackatdac21/blob/58f984d492fdb0369c82ef10fcbbaa4b9850f9fb/piton/design/chip/tile/ariane/src/riscv-dbg/src/dmi_jtag.sv#L200

REF-1353

Fix CWE-1191 in dmi_jtag.sv
Florian Zaruba.
https://github.com/HACK-EVENT/hackatdac21/blob/58f984d492fdb0369c82ef10fcbbaa4b9850f9fb/piton/design/chip/tile/ariane/src/riscv-dbg/src/dmi_jtag.sv#L131

REF-1352

dmi_jtag.sv
Florian Zaruba.
https://github.com/HACK-EVENT/hackatdac21/blob/71103971e8204de6a61afc17d3653292517d32bf/piton/design/chip/tile/ariane/src/riscv-dbg/src/dmi_jtag.sv#L118:L204

REF-1364

dmi_jtag.sv
https://github.com/HACK-EVENT/hackatdac21/blob/71103971e8204de6a61afc17d3653292517d32bf/piton/design/chip/tile/ariane/src/riscv-dbg/src/dmi_jtag.sv#L82

REF-1365

fix cwe_1205 in dmi_jtag.sv
https://github.com/HACK-EVENT/hackatdac21/blob/c4f4b832218b50c406dbf9f425d3b654117c1355/piton/design/chip/tile/ariane/src/riscv-dbg/src/dmi_jtag.sv#L158

Submission

Modifications