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Base · Medium

CWE-1259: Improper Restriction of Security Token Assignment

The System-On-A-Chip (SoC) implements a Security Token mechanism to differentiate what actions are allowed or disallowed when a transaction originates from an entity. However, the Security Tokens are...

CWE-1259 · Base Level ·1 Mitigations

Description

The System-On-A-Chip (SoC) implements a Security Token mechanism to differentiate what actions are allowed or disallowed when a transaction originates from an entity. However, the Security Tokens are improperly protected.

Systems-On-A-Chip (Integrated circuits and hardware engines) implement Security Tokens to differentiate and identify which actions originated from which agent. These actions may be one of the directives: 'read', 'write', 'program', 'reset', 'fetch', 'compute', etc. Security Tokens are assigned to every agent in the System that is capable of generating an action or receiving an action from another agent. Multiple Security Tokens may be assigned to an agent and may be unique based on the agent's trust level or allowed privileges. Since the Security Tokens are integral for the maintenance of security in an SoC, they need to be protected properly. A common weakness afflicting Security Tokens is improperly restricting the assignment to trusted components.

Potential Impact

Confidentiality, Integrity, Availability, Access Control

Modify Files or Directories, Execute Unauthorized Code or Commands, Bypass Protection Mechanism, Gain Privileges or Assume Identity, Modify Memory, Modify Memory, DoS: Crash, Exit, or Restart

Demonstrative Examples

For example, consider a system with a register for storing an AES key for encryption and decryption. The key is of 128 bits implemented as a set of four 32-bit registers. The key register assets have an associated control register, AES_KEY_ACCESS_POLICY, which provides the necessary access controls. This access-policy register defines which agents may engage in a transaction, and the type of transaction, with the AES-key registers. Each bit in this 32-bit register defines a security Token. There could be a maximum of 32 security Tokens that are allowed access 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 and, if "0" (i.e., Clear), disallows the respective action to that corresponding agent.
Let's assume the system has two agents: a Main-controller and an Aux-controller. The respective Security Tokens are "1" and "2".
An agent with Security Token "1" has access to AES_ENC_DEC_KEY_0 through AES_ENC_DEC_KEY_3 registers. As per the above access policy, the AES-Key-access policy allows access to the AES-key registers if the security Token is "1".
Bad
The Aux-controller could program its Security Token to "1" from "2".
The SoC does not properly protect the Security Token of the agents, and, hence, the Aux-controller in the above example can spoof the transaction (i.e., send the transaction as if it is coming from the Main-controller to access the AES-Key registers)
Good
The SoC needs to protect the Security Tokens. None of the agents in the SoC should have the ability to change the Security Token.

Mitigations & Prevention

Architecture and DesignImplementation

CWE-284: Improper Access Control

The product does not restrict or incorrectly restricts access to a resource from an unauthorized actor.

CWE-1294: Insecure Security Identifier Mechanism

The System-on-Chip (SoC) implements a Security Identifier mechanism to differentiate what actions are allowed or disallo...

Frequently Asked Questions

What is CWE-1259?

CWE-1259 (Improper Restriction of Security Token Assignment) is a software weakness identified by MITRE's Common Weakness Enumeration. It is classified as a Base-level weakness. The System-On-A-Chip (SoC) implements a Security Token mechanism to differentiate what actions are allowed or disallowed when a transaction originates from an entity. However, the Security Tokens are...

How can CWE-1259 be exploited?

Attackers can exploit CWE-1259 (Improper Restriction of Security Token Assignment) to modify files or directories, execute unauthorized code or commands, bypass protection mechanism, gain privileges or assume identity, modify memory, modify memory, dos: crash, exit, or restart. This weakness is typically introduced during the Architecture and Design, Implementation phase of software development.

How do I prevent CWE-1259?

Key mitigations include:

What is the severity of CWE-1259?

CWE-1259 is classified as a Base-level weakness (Medium abstraction). Its actual severity depends on the specific context and how the weakness manifests in your application.