CWE-1328 Security Version Number Mutable to Older Versions

The security version number in the hardware product is mutable, resulting in the ability to downgrade (roll-back) the boot firmware to vulnerable code versions.

• Confidentiality, Integrity, Authentication, Authorization: Other, Alter Execution Logic, Unexpected State — If the security version number is modifiable by an adversary, this allows attacks like downgrading to a previous version that contains vulnerabilities. Once downgraded to a previous version, an adversary can launch exploits on the SoC and thus compromise the security of the SoC. These downgrade attacks are also referred to as roll-back attacks. • Availability: Other, Alter Execution Logic, Unexpected State — An adversary could prevent upgrades, casing a denial of service.

• [Architecture and Design] The security version number must be stored securely and persistently across power-on resets. When architecting the system, security version data should be designated for storage in registers that are either read-only or have access controls that prevent modification by an untrusted agent. • [Implementation] During implementation and test, security version data should be demonstrated to be read-only and access controls should be validated.

• Automated Dynamic Analysis: Mutability of stored security version numbers and programming with older firmware images should be part of automated testing. • Architecture or Design Review: Anti-roll-back features should be reviewed as part of Architecture or Design review.