CWE-1224 Improper Restriction of Write-Once Bit Fields

The hardware design control register "sticky bits" or write-once bit fields are improperly implemented, such that they can be reprogrammed by software.

• Confidentiality, Integrity, Availability, Access Control: Varies by Context, Modify Memory — System configuration cannot be programmed in a secure way. Failure to implement write-once restrictions in hardware design can expose such registers to being re-programmed by software and written multiple times. For example, write-once fields could be implemented to only be write-protected if they have been set to value "1", wherein they would work as "write-1-once" and not "write-once".

• [Architecture and Design] During hardware design, all register write-once or sticky fields must be evaluated for proper configuration.

• Automated Analysis: Use automated tools to test that values are not reprogrammable and that write-once fields lock on writing zeros.