Missing Security Identifier

The product implements a security identifier mechanism to differentiate what actions are allowed or disallowed when a transaction originates from an entity. A transaction is sent without a security identifier.


Description

In a System-On-Chip (SoC), various integrated circuits and hardware engines generate transactions such as to access (reads/writes) assets or perform certain actions (e.g., reset, fetch, compute). A typical transaction is comprised of source identity (to identify the originator of the transaction) and a destination identity (to route the transaction to the respective entity) in addition to much more information in the message. Sometimes the transactions are qualified with a Security Identifier. This Security Identifier helps the destination agent decide on the set of allowed or disallowed actions.

A common weakness that can exist in such transaction schemes is that the source agent fails to include the necessary, security identifier with the transaction. Because of the missing security identifier, the destination agent might drop the message, thus resulting in Denial-of-Service (DoS), or get confused in its attempt to execute the given action, which confusion could result in privilege escalation or a gain of unintended access.

Demonstrations

The following examples help to illustrate the nature of this weakness and describe methods or techniques which can be used to mitigate the risk.

Note that the examples here are by no means exhaustive and any given weakness may have many subtle varieties, each of which may require different detection methods or runtime controls.

Example One

Consider a system with a register for storing AES key for encryption or decryption. The key is of 128 bits implemented as a set of four 32-bit registers. The key registers are assets, and the register AES_KEY_ACCESS_POLICY is defined to provide the necessary access controls.

The access-policy register defines which agents with a security identifier in the transaction can access the AES-key registers. Each bit in this 32-bit register defines a security identifier. There could be a maximum of 32 security identifiers that are allowed accesses to the AES-key registers. The number of the bit when set (i.e., “1”) allows for a respective action from an agent whose identity matches the number of the bit; if set to “0” (i.e., Clear), it disallows the respective action to that corresponding agent.

RegisterField descriptionAES_ENC_DEC_KEY_0AES key [0:31] for encryption or decryption, Default 0x00000000AES_ENC_DEC_KEY_1AES key [32:63] forencryption or decryption, Default 0x00000000AES_ENC_DEC_KEY_2AES key [64:95] for encryption or decryption, Default 0x00000000AES_ENC_DEC_KEY_4AES key [96:127] for encryption or decryption, Default 0x00000000AES_KEY_ACCESS_POLICY[31:0] Default 0x00000004 – agent with Security Identifier “2” has access to AES_ENC_DEC_KEY_0 through AES_ENC_DEC_KEY_4 registers

The originator sends a transaction with no security identifier, i.e., meaning the value is “0” or NULL. The AES-Key-access register does not allow the necessary action and drops the transaction because the originator failed to include the required security identifier.

RegisterField descriptionAES_ENC_DEC_KEY_0AES key [0:31] for encryption or decryption, Default 0x00000000AES_ENC_DEC_KEY_1AES key [32:63] forencryption or decryption, Default 0x00000000AES_ENC_DEC_KEY_2AES key [64:95] for encryption or decryption, Default 0x00000000AES_ENC_DEC_KEY_4AES key [96:127] for encryption or decryption, Default 0x00000000AES_KEY_ACCESS_POLICY[31:0] Default 0x00000002 – agent with security identifier “2” has access to AES_ENC_DEC_KEY_0 through AES_ENC_DEC_KEY_4 registers

The originator should send a transaction with Security Identifier “2” which will allow access to the AES-Key-access register and allow encryption and decryption operations.

See Also

Core and Compute Issues

Weaknesses in this category are typically associated with CPUs, Graphics, Vision, AI, FPGA, and microcontrollers.

Privilege Separation and Access Control Issues

Weaknesses in this category are related to features and mechanisms providing hardware-based isolation and access control (e.g., identity, policy, locking control) of s...

Comprehensive CWE Dictionary

This view (slice) covers all the elements in CWE.

Weaknesses without Software Fault Patterns

CWE identifiers in this view are weaknesses that do not have associated Software Fault Patterns (SFPs), as covered by the CWE-888 view. As such, they represent gaps in...

Weaknesses Introduced During Implementation

This view (slice) lists weaknesses that can be introduced during implementation.


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